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MID TEST (UTS) Basic Chemistry I

MID TEST (UTS) Basic Chemistry I

NIM : RSA1C112011

  1.   Question :
    1.   pure substance X is solid at room temperature. if the substance is heated to 2300C is melted gradually. if then cooled to room temperature, the liquid can not be frozen
    a.        is it possible X of an element or a compound. explain it!

    answer :
    I think X is a compound substance because the substance X there is a temperature or temperature where it shows the boiling point and melting point where the reaction can be smelted though gradually. And also substance X indicates the compound is ionic compound shown by the boiling point and high melting.

    b.      does it a chemical change occured? if so can it be said to undergo an endoterm changing, based on the information provided?

    answer :
    Substance X can be regarded as a change when heated at a temperature of 2300C occurred a little fusion, albeit slightly. Consolidation is changing the substance X from solid to liquid.

    c.       Can it be said that the liquid is an element, based on the information provided

    answer :
    I think that could be because the elements are part of the underlying basis of something where, the fluid element is an element that is composed of elements / structure of an element that is liquid or liquid. such as hydrogen and oxides that react to H2O.  

      Question :
    2.       When a candle that weight 10 gr is burned in oxygen, carbon dioxide and water vapor formed by combustion the weight more than 10 gr. Was this case match with the law of mass. Explain it.

    answer :
    It is not contrary to the law of conservation of mass, due to the law of conservation of mass is explained that the mass of a substance before and after the same or unchanged. And also in the reaction above Hannya weight change and explained that there was no mass change. So it belongs to the law of conservation of mass.

      Question :
    3.       When carbon burns in oxygen under limited number, it will form two gaseous compounds. Suggest the way to differentiate the two compounds with one another.

    answer :
    In my opinion, to differentiate the two compounds formed from carbon gas that burns oxygen. To do the experiment qualitatively to distinguish or know the chemical to know the difference.

      Question :
    4.       After mendeev compiled theperiodic table, he conclude that the atomic weight of certain elements was wrong ruling, and this conclusion was apparently correct. How Mendeleev was able to predict that several atomic weight were wrong? Why his predictions are not always right. Explain!

    answer :
    Predictions are not always correct because the periodic Mendelev, long periods in the periodic system are not the same and why not described. That is what makes his predictions are not always right.

      Question :
    5.       When an aqueous mercury chloride solution is added to an aqueous solution of silver nitrate, a white solid forms. Identify the white solid and write the balanced equation for the reaction that occurs.

    answer :
    HgCl2 + 2AgNO3 à Hg (NO3)2 + 2AgCl

Electronegativity of The Periodic Trends

Electronegativity is a measure of the ability of an atom or molecule to attract electron pairs in the context of chemical bonds.Electronegativity can not be calculated directly, but must be calculated from the properties of atoms and molecules. Several methods of calculation have been proposed. Although in every method there is little difference in the numerical value of the electronegativity, all methods have the same trend in the period between the elements.
 The most commonly used method is the method of Pauling. The results of this calculation produces a dimensionless value and is usually referred to as the Pauling scale relative scale that ranged from 0.7 to 4.0 (hydrogen = 2.2). When other methods of calculation is used, there is a convention (although not required) to use the same scale range Pauling scale: this is known as an electronegativity in Pauling units.
Electronegativity is not part of the nature of the atom, but only the nature of atoms in molecules. Properties of single atoms is equal to the electron affinity electronegativity. Electronegativity in an element will vary depending on the chemical environment, but it is usually regarded as a property of displaced, an electronegativity value is considered to apply to various situations vary.
Carbon-fluorine bond
Fluorine is much more electronegative than carbon. Original value Pauling scale is
This means that the fluorine attract electrons more strongly than carbon. Ties on average will look like this:


Carbon-chlorine bond
Its electronegativity is:

Pair bonding electrons will be drawn to chlorine but not as strong as in florins. Because chlorine is not senegatif florins.

  Bond polarity and inductive effects
Polarity bond
Think about the carbon-fluorine bond again. Because the bonding pair of electrons pulled towards the side of the florin would be more negative. While the pair of carbon becomes slightly more electron deficiency and be more positive.
symbols + and - means "more positive" and "more negative". + Read with the "delta plus" or "positive delta".
We describe a bond that has the more negative and more positive as polar.
  Inductive effect
A fluorine atom as to attract the electron pair bond is said to have a negative inductive effect.
Most of the atoms that you would have encountered mostly have negative inductive effect when bonded to carbon because they are more electronegative than carbon.
 You will also find some group of atoms that has little inductive effect posotif. They push the electrons to the carbon they are bonded and makes it more negative.
Inductive effects are often given the symbol: I-(negative inductive effect) and + I (positive inductive effect).
  Some important examples of polar bonds
Hydrogen Bromide (and other hydrogen halides)
Bromine (halogen and others) are all more electronegative than hydrogen halide and all hydrogen bonds have polar bonds with the hydrogen halides are more positive and more negative parts.
The polarity of these molecules is crucial as they react with alkenes.
Carbon-bromine bond in Halogenoalkena
Bromine is more electronegative than carbon that bonds polarized as we have language support in CF and C-l.

The polarity of the carbon-halogen important in halogenoalkanes reaction.

Carbon-oxygen bond
A model orbital of the C = O at methanal, CHCHO, looks like this:
The most electronegative oxygen atoms attract both spouses ties to him. And it resulted in more negative oxyg

The atomic structure

The structure of an atom is the basic unit of matter consisting of a nucleus and its negatively charged electron cloud surrounding it. The nucleus contains a mix of positively charged protons and electrically neutral neutrons (except in Hydrogen-1 which has no neutrons). The electrons in an atom bound to the nucleus by the electromagnetic force. Similarly, a collection of atoms can bind to each other to form a molecule. Atoms containing the number of protons and electrons of the same neutral, while containing the number of protons and electrons of different positive or negative and is ion. Atoms are grouped based on the number of protons and neutrons in the atomic nucleus. The number of protons in an atom determines the chemical element the atom, and the number of neutrons determine the isotope of the element.
Kinds of Model Atom
Dalton said that atoms like a solid ball or a ball shot put JJ.Thomson say that ATOMM like raisin bread E.Rutherford atom like the solar system suggests
1. John Dalton Atomic Model
In 1808, John Dalton, who is a teacher in the UK, contemplating on the atom. Results reflection refine Dalton's atomic theory of Democritus. Shadow Dalton and Democritus is that the atoms of solid shape. In Dalton argued postulatnya musings about atoms:
1. Each element is composed of extremely small particles called atoms with
2. Atoms of the same element the same properties memiliiki
3. Atoms of different elements have different properties
4. Atoms of an element can not be converted into atoms of another element with the chemical reaction, atoms can not be destroyed and the atoms also can not be destroyed
5. Atoms can combine to form atoms called molecules combined
6. In the compound, the mass ratio of each element is fixed
Dalton's atomic theory began to arouse interest in the study of atomic models. However, Dalton's atomic theory has shortcomings, which can not explain a solution to conduct electrical current. How could solid ball can conduct electricity when electricity is electrons moving. Meaning there are other particles that can conduct aruslistrik.
2. J.J. Atom Model Thomson
The downside of Dalton repaired by JJ. Thomson, experiments are done kotoda ray tube. The results of experiments stated there negatively charged particles called electrons in atoms. A ball of solid surface surrounded by electrons and other particles that are positively charged atom is neutral. Thomson model of atom images:
Weakness Thomson models can not explain the arrangement of positive and negative charges within the atomic sphere.

Weakness Thomson atomic model
Thomson's model can not explain the arrangement of positive and negative charges within the atomic sphere.
3. Rutherford Atom Model
Rutherford model of the atom
Rutherford conducted a study on α-ray scattering on gold plates. Observations were developed in the Rutherford atomic model hypothesis.
a. Most of the atom is empty surface.
b. Atom has a positively charged nucleus which is the center of mass of the atom.
c. Electrons move around the nucleus at a very high speed.
d. Most of the α particles pass without having distorting / barriers. A small portion deflected, and little is reflected.

Weakness Rutherford Atom Model
a. According to the laws of classical physics, electrons moving around the nucleus emits energy in the form of electromagnetic waves. As a result, the electron eventually it will run out of energy and eventually attached to the core.
b. Rutherford atomic model has not been able to explain where the location of the electron and the way the rotation of the nucleus.
c. Electrons emit energy when moving, so the energy of the atom becomes unstable.
d. Unable to explain the line spectrum of hydrogen atoms (H).

4. Niels Bohr Atom Model
Niels Bohr Atom Model

In 1913, Niels Bohr expressed the opinion that the electrons moving around the nucleus in certain paths called shells. Bohr's atomic model is a refinement of the atomic model of Rutherford.

Rutherford's atomic theory weaknesses corrected by Neils Bohr to postulate Bohr:
a. Electrons surrounding the nucleus has a certain trajectory and energy.
b. In particular orbital, the electron energy is fixed. The electrons will absorb energy when moving to the outer orbit and will release energy when moving deeper into orbit
Excess Bohr model of the atom
atom consists of a few skins for a transfer of electrons.

Weakness Bohr model of the atom
a. can not explain the Zeeman effect and the effect Strack.
b. Unable to explain the events of the chemical bond well, the influence of magnetic fields on atoms and atomic electron spectrum more.
1. The principal quantum number (n): states in which the electron energy levels are
n has a price of 1, 2, 3, .....
- N = 1 corresponds to the K shell
- N = 2 correspond to the L shell
- N = 3 corresponds to the skin M
- And so on
Each skin or any number of energy levels occupied by electrons. The number of electrons that can occupy maksimmm energy levels must satisfy the Pauli formula = 2N2.
skin-to-4 (n = 4) can be occupied by a maximum = 2 x 42 electrons = 32 electrons
2. Azimuthal quantum number (l): indicate sub skin where the electron also shows sub skin which is a constituent of skin.
Azimuthal quantum number have prices from 0 to (n-1).
n = 1; l = 0; corresponding K shell
n = 2, l = 0, 1; corresponding L shell
n = 3; l = 0, 1, 2; appropriate skin M
n = 4; l = 0, 1, 2, 3; appropriate skin N
and so on
Sub leather prices vary is given a special name:
l = 0; fit leather sub s (s = sharp)
l = 1; fit leather sub p (p = principle)
l = 2; fit leather sub d (d = diffuse)
l = 3; fit leather sub f (f = fundamental)
Magnetic quantum number (m): ataubeberapa realize that there is a level of energy in a sub shell. Magnetic quantum number (m) has a price (-l) to price (+ l).

l = 0 (sub leather s), price m = 0 (having 1 orbital)
l = 1 (p sub shell), price m = -1, O, +1 (have 3 orbitals)
l = 2 (sub skin d), price m = -2, -1, O, +1, +2 (have 5 orbitals)
l = 3 (sub kwit f), price m = -3, -2, O, +1, +2, +3 (has 7 orbitals)
4. Spin quantum number (s): indicates the direction of rotation of the electron on its axis.
In one orbital, maximum of 2 electrons can circulate and the two electron spins through the axis in the opposite direction, and each is priced spin +1 / 2 or -1 / 2.
Aufbau principle
Aufbau principle that electrons fill orbitals starting at the lowest energy level to a higher energy level.
according to this rule, the order of filling orbitals are as follows:
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p
The principle of prohibition pauli
Pauli principle states that the ban is not possible in an atom there are two electrons that are priced the same four quantum biulangan.

Rule hund
According to the rules hund, filling electrons in orbitals of the same energy level, the electrons do not form pairs of electrons before each filled with an electron orbital.
24Cr :

Energy and Chemical Reactions

A chemical reaction is a process of breaking and bond formation. The process is always accompanied by energy changes. The energy required to break chemical bonds, thus forming free radicals called the bond energy. For complex molecules, the energy required to break the molecule to form free atoms called atomization energy.
Atomization energy prices is the amount of the bond energy of the atoms in the molecule. For covalent molecule consisting of two atoms such as H2, 02, N2 or HI which has a bond equal to the energy of atomization energy bond energy of atomization of a compound can be determined by the help enthalpy of formation of these compounds. Mathematically it can be described by the equation:

DH = S bond breaking energy - S energy bond formation

     =  bond energy on the left - bond energy in the right

bond energy
C - H = 414.5 kJ / mole
C = C = 612.4 kJ / mol
C - C = 346.9 kJ / mol
H - H = 436.8 kJ / mol

D H = reaction C2H4 (g) + H2 (g) ® C2H6 (g)

 H reaction = Total bond breaking energy - amount of energy bond formation
= (4 (C-H) + (C = C) + (H-H)) - (6 (C-H) + (C-C))
= ((C = C) + (H-H)) - (2 (C-H) + (C-C))
= (612.4 + 436.8) - (2 x 414.5 + 346.9)
= - 126.7 kJ

 Enthalpy and Enthalpy Changes

1. System and environment
The system is a chemical reaction that is being observed or studied. While the so-called environment is everything outside the system. Example: if we are reacting metals Mg and HCl in a test tube, the substances contained in the test tube called a system and apart from that is the environment.

In the example above the center of attention is the metal Mg and HCl solution. Thus, metallic Mg and HCl solution called the system, whereas the reaction tube, air temperature, air pressure is the environment. Based on interaction with the environment, the system can be divided into three kinds, namely:

a. Open System, a system that allows the exchange of heat and matter (material) between the environment and the system.
b. Closed system, a system which allows the exchange of heat between the system and its environment, but not an exchange of material.
c. Isolated Systems (sealed), a system that does not allow the exchange of heat between the system and the environment danmateri.

2. Energy and enthalpy
In any chemical reaction is always a change of energy.
Energy units:
1 calorie = 4.184 Joules
1 kJ = 1000 Joules
1 kcal = 1000 calories
1kkal = 4.184 k J

Overall energy possessed by a system in a particular state is called energy (U). Energy in a state function, depends only on the state of the system (temperature, volume, pressure, and number of moles), does not depend on the path through the system. Energy can not be measured but the changes can be measured. If the change occurs at a constant pressure (open system), the energy changes that occur in the so-called enthalpy change.

Chemical reactions are generally carried out in an open system (fixed pressure).
Therefore, in any process that involves a change in volume due to constant pressure, there is the work that accompanies the process although a small but significant.
According to the Law of Thermodynamics I (Law of Conservation of Energy),
H = U + PV
The enthalpy change is expressed by the equation:
H = U + PV
From the equation it can be concluded that if the reaction is carried out at a constant pressure the heat changes that occur will be equal to the enthalpy change for the pressure change 0 (Zero). Thus, the enthalpy equal to the amount of energy stored in a system. So the enthalpy (H) is the energy stored in the form of heat in a system.

3. Enthalpy change
The enthalpy change of a system can be measured if the system is changing.
Enthalpy changes (H):
If a reaction takes place at a constant pressure, the change in enthalpy equal
the heat that must be removed from the system into the environment or otherwise that
temperature of the system back to its original state.
H = qp (qp = heat of reaction at constant pressure)
The magnitude of the enthalpy change is the difference in magnitude of the enthalpy of the system after a change in the magnitude of the enthalpy of the system before the changes at a constant pressure.

H = H final - H initial

The enthalpy change accompanying a reaction is influenced by:
• The number of substances
• physical state of a substance
• Temperature (T)
• Pressure (P)

4. Reaction was exothermic and endothermic reactions
1. Exothermic reaction is a reaction that releases heat or energy from the system to the environment.
Enthalpy reduced system (the reaction products have a lower enthalpy than the original substance).
H final <H initial
H final - H initial <0
H negative value

The reaction between calcium oxide (quicklime) and Cretaceous shallow water put into the water in a test tube. This reaction takes place is characterized by a mixture of temperature rise (the system). Because the temperature of the system is higher than the environment, the heat will come out of the system into the environment until they become the same temperature.
CaO (s) + H2O (l) Ca (OH) 2 (aq)

2. Endothermic reaction is a reaction that absorbs heat or energy needs from the environment to the system.
Enthalpy system is improved (the reaction has a higher enthalpy than the original substance).
H final> H initial
H final - H initial> 0
H positive value

The reaction between barium hydroxide crystals oktahidrat with ammonium chloride crystals.
When barium hydroxide crystals oktahidrat, Ba (OH) 2. 8H2O crystals mixed with ammonium chloride (NH4Cl), the reaction takes place immediately marked by a drop in temperature and the formation of a mixture of ammonia gas. Therefore temperature of the mixture (the system) will be lower than the environment, the heat will flow from the environment into the system until they become the same temperature. Ba (OH) 2. 8H2O (s) + 2NH4Cl BaCl2.2H2O (s) + 2NH3 (g) + 8H2O (l)

5. Thermochemical Equations
The equation that describes the reaction with the information about the change in enthalpy (heat). Because enthalpy is extensive properties (value depends on the magnitude and size of the system) then the thermochemical equation also listed the number of moles of a substance expressed reaction coefficient, and the phase state of the substance involved.

a. In the formation of 1 mol of water from hydrogen gas with oxygen gas at 25 ° C
(298 K), 1 atm, was 286 kJ of heat is released.
Thermochemical equations of the above statement is
The word "released" state that quite exothermic reaction. Therefore, the
H = -286 kJ per mole of water formed.
H2 (g) + O2 (g) H2O () H = -286 kJ
2H2 (g) + O2 (g) 2H2O () H = -572 kJ

b. The reaction of carbon and hydrogen to form 1 mole of C2H2 at temperatures of 25oC
and a pressure of 1 atm requires 226.7 kJ of heat.
Termokimianya equation:
The word "need" states that belong to endothermic reactions.
2 C (s) + H2 (g) C2H2 (g) + H = 226.7 kJ

6. Standard enthalpy change (Ho)
Reaction enthalpy changes measured at 25oC temperature (298 K) and
pressure of 1 atm was agreed as the standard enthalpy change, otherwise
with the symbol Ho
The state standard is needed because measurements at different temperatures and pressures will result in prices that different enthalpy changes. Units used to express the change in enthalpy is kJ. Changes in molar enthalpy is kJ / mol.

Enthalpy change based on the type of chemical changes that occur:
1. Standard enthalpy change of formation (Hf o)
(Hf o = standard enthalpy of formation)
Is the enthalpy change for the formation of 1 mole of a compound from its elements are the most stable, the standard state. Unit change in standard enthalpy of formation according to the International System (SI) is kJ / mol.
Changes from the standard enthalpy of formation of carbon dioxide (CO2) is -393.5 kJ / mol.
Termokimianya equation:
C (s) + O2 (g) CO2 (g) Hf
o = -393.5 kJ / mol

2. Standard enthalpy change of decomposition (Hd o)
(Hd o = standard enthalpy of decomposition)
Is the enthalpy change for the decomposition of 1 mole of a compound into its elements, the standard state.
Enthalpy change for the decomposition of H 2 O is +286 kJ / mol.
Termokimianya equation:
H2O () H2 (g) + O2 (g) Hd
o = + 286 kJ / mol

3. Standard enthalpy change of combustion (Hc o)
(Hc o = standard enthalpy of combustion)
Is the change in enthalpy in the combustion of 1 mol element or compound at standard conditions. Combustion is the reaction of a substance with oxygen.


Stoichiometry is the study and calculate the quantitative relationships of the reactants and products in chemical reactions (chemical equations). The word is derived from the Greek stoikheion (elements) and metriā (size).
Determination of the reaction stoichiometry is the mass ratio of the elements in a compound in the formation of compounds. In the calculation of chemical stoichiometry, usually required fundamental laws of chemistry. basic laws of chemistry, the law of conservation of mass, the law of comparative fixed, and multiple comparative law.
Stoichiometric gas is a particular form, in which the reactants and products entirely in the form of gas. In this case, the coefficient of substance (mole ratio stating the reaction stoichiometry) also has stated volume ratio between the substances involved.

a. The initial phase of stoichiometric
At the beginning of chemistry, quantitative aspects of chemical change, the chemical reaction stoichiometry, did not get much attention. Even when attention has been given, experimental techniques and tools do not produce correct results.
One example involves the theory of phlogiston. Flogistonis tried to explain the phenomenon of combustion with the term “flammable substance”. According to the flogitonis, combustion is a release of flammable substances (from the burning substance). This substance was later called “phlogiston”. Based on this theory, they defined as the release of phlogiston combustion of flammable substances. Mass changes when burning wood fits well with this theory. However, the change in mass of metal when calcined does not match the theory. However flogistonis accept that the two processes are essentially identical. Increasing the mass of calcined metal is a fact. Flogistonis tried to explain this anomaly by stating that phlogiston negative mass.
Philosophers of Flanders January Baptista van Helmont (1579-1644) experimented “willow” famous. He is growing seedlings of willow after measuring the mass of flower pots and soil. Since there is no mass change flower pots and soil when the seed grows, it assumes that the masses were obtained only because of water coming into the ore. He concludes that “the root of all matter is water”. Based on the current outlook, hypothesis and experiment are far from perfect, but the theory is a good example of the attitude of the quantitative aspects of chemistry that are growing. Helmont recognize the importance of stoichiometry, and clearly ahead of his time.
In the late 18th century, German chemist Jeremias Benjamin Richter (1762-1807) invented the concept of equivalent (in terms of modern chemistry chemical equivalent) with a reaction carefully acid / base, the quantitative relationship between acids and bases in the neutralization reaction. Equivalent Richter, or what is now called the chemical equivalent, indicating a certain amount of material in the reaction. The neutralization equivalent in regard to the relationship between the number of acid and a base for mentralkannya. Proper knowledge is essential to produce the equivalent of soap and gunpowder good. Thus, such knowledge is very important in practice.
At the same time Lavoisier established the law of conservation of mass, and provide a basis equivalent to the concept of an accurate and creative experiments. Thus, the stoichiometry handle the quantitative aspects of chemical reactions into chemical basic methodology. All the fundamental laws of chemistry, of the law of conservation of mass, the law of comparative law remains until all based gas reaction stoichiometry. Fundamental laws are the basis of the atomic theory, and consistently explained by atomic theory. However, it is interesting to note that the concept of equivalent used before atomic theory was introduced.

b. The relative atomic mass and atomic mass
Dalton recognized that it is important to determine the mass of each atom as mass varies for each type of atom. Atom is very small so it is not possible to determine the mass of a single atom. So he focuses on the relative masses and create a table atomic mass (Figure 1.3) for the first time in human history. In the table, the mass of the lightest element, hydrogen adoption as a standard one (H = 1). Atomic mass is a relative value, meaning that a dimensionless ratio. Although several different atomic masses with modern values, most of the proposed values ​​in the range of compatibility with the current value. This shows that the idea and the experiment right.
Then the Swedish chemist Jons Jakob Berzelius Baron (1779-1848) to determine the mass of the oxygen atom as the standard (O = 100). Because Berzelius get this value based on the analysis of oxide, it has a clear reason to choose oxygen as standard. However, the standard hydrogen is clearly superior in terms of simplicity. Now, after much discussion and modification, carbon standard is used. In this method, the mass of 12C carbon with 6 protons and 6 neutrons is defined as 12.0000. Atomic mass is the mass of an atom relative to this standard. Although carbon has been declared as standard, this can actually be considered as a standard hydrogen is modified.
Atomic mass of almost all the elements very close to integers, ie integer multiples of hydrogen atomic mass. This is a natural kosekuensi fact that the hydrogen atom mass equal to the mass of a proton, which in turn is almost equal to the mass of a neutron, and electron mass is very small to negligible. However, most of the naturally occurring element that is a mixture of several isotopes, and atomic mass depends on the distribution of isotopes. For example, the atomic mass of hydrogen and oxygen is 1.00704 and 15.9994. The mass of the oxygen atom is very close to the value of 16 is a bit smaller.

Molecular mass and formula mass
Each compound is defined enumerated by a chemical formula that indicates the type and number of atoms that make up compound. The mass formula (or formula mass) is defined as the sum of the atomic masses based on the type and number of atoms in the chemical formula defined. The chemical formula of molecules called molecular formula, chemical formula and mass is called the mass molekul.5 example, the molecular formula of carbon dioxide is CO2, and the molecular mass is 12 + (2x 6) = 44. As the mass of the atom, both mass and molecular mass formula should not be an integer. For example, the molecular mass of hydrogen chloride HCl is 36.5. Even if the type and number of atoms that make up molecules are identical, the two molecules may have different molecular masses when there are different isostop involved.
It is impossible to define molecules for compounds such as sodium chloride. Mass formula for sodium chloride is used instead of molecular mass.
c. Quantity of matter and mole
Quantitative methods most suited to express the amount of matter is the number of particles such as atoms, molecules that make up the material being discussed. However, to calculate the atomic or molecular particles are very small and can not be seen very difficult. Instead of counting the number of particles is directly the number of particles, we can use the mass of a certain number of particles. Then, how does a certain amount of numbers chosen? For
long story short, the number of particles in a 22.4 L of gas at STP (0 ℃, 1ATM) was selected as the standard amount. This number is called Avogadro’s number. Name number Loschmidt also proposed to honor the Austrian chemist Joseph Loschmidt (1821-1895) who first with the experiment (1865).
Since 1962, according to the SI (Systeme Internationale) decided bahwam in the world of chemistry, mole is used as a unit of the amount of matter. Defined Avogadro’s number of carbon atoms in 12 g 126C and renamed Avogadro constant.
There are several definitions of “mole”:
(I) The amount of material that contains a number of particles contained in 12 g of 12C. (Ii) one mole of material that contains Avogadro constant number of particles.
(Iii) A material that contains 6.02 x 1023 particles in one mole.
d. Atomic mass units (sma)
Because the standard atomic mass is the mass of hydrogen Dalton system, standard mass in the right SI 1/12 the mass of 12C. This value is called the atomic mass unit (sma) and is equal to 1.6605402 x 10-27 kg, and D (Dalton) is used as a symbol. Atomic mass is defined as the ratio of the average sma elements with natural isotopic distribution with 1/12 sma 12C.
Chemical law is a law of nature that are relevant to the field of chemistry. The most fundamental concept in chemistry is the law of conservation of mass, which states that no changes in the quantity of matter during an ordinary chemical reaction.
Additional law in chemistry to develop the law of conservation of mass. Comparative law remains of Joseph Proust states that pure chemicals are composed of elements with a certain formula we now know that the structural arrangement of these elements are also important.
Multiple comparisons law of John Dalton stated that the chemicals will be present in the form of the proportion of small integers (eg 1:2; O: H in water = H2O), although in many systems (especially Biomacromolecules and minerals) this ratio tends require large numbers, and is often given in the form of fractions. Such compounds are known as non-stoikhiometrik compounds.
Another modern chemical law to determine the relationship between energy and transformation.
a. In equilibrium, a molecule found in the mixture is determined by the transformations that may occur on a time scale equilibrium, and has a ratio determined by the intrinsic energy of the molecule. The smaller the intrinsic energy, the more molecules.
b. Change one structure into another structure requires the input of energy to overcome the energy barrier: this can be caused by intrinsic energy molecule itself, or from external sources will generally accelerate the change. The greater the energy barrier, the slower the process of ongoing transformation.
c. There is a structure or a transition between the hypothetical, which relates to the structure at the top of the energy barrier. Hammond Postulate-Leffer stated that this structure resembles origin products or materials that have intrinsic energy closest to the energy barrier. By stabilizing the hypothetical structure with the chemical interaction is one way to achieve catalysis.
d. All chemical processes are irreversible (reversible) (microscopic keterbalikkan legal) process has a bias although some energy, they basically takterbalikkan (irreversible).


4 Comments 08 OCTOBER 2012
A chemical reaction is a process in which new substances that the reaction proceeds, the original form of some substances, called reactants. Usually a chemical reaction accompanied by physical events, such as discoloration, sludge formation, or the onset of gas. Chemical reactions are usually characterized by a chemical change, and will produce one or more products that typically have characteristics that are different from the reactants. Classically, chemical reactions involve changes involving the movement of electrons in the forming and breaking of chemical bonds, although the general concept is basically a chemical reaction can also be applied to the transformation of elementary particles such as the nuclear reaction.
Reactions with different chemical used in chemical synthesis to produce the desired compound. In biochemistry, series of chemical reactions catalyzed by enzymes form metabolic pathways, in which the synthesis and decomposition is usually not possible in the cell do.
Equation used to describe chemical reactions. Equation consists of a chemical formula or structural formula of the reactants on the left and the right products. Between products and reactants are separated by arrows (→) which indicates the direction and type of reaction. The tip of the arrow shows which way the reaction moves. Double arrow (), which has two different ends direction arrows, used in the equilibrium reaction. Chemical equations must be balanced according to the stoichiometry, the number of atoms of each element on the left must equal the number of atoms of each element on the right. Balancing is done by adding the numbers in front of each molecule compounds (denoted by A, B, C and D in the schematic diagram below) with a small number (a, b, c and d) in the future.
aA + bB —> cC + dD
More complicated reactions represented by reaction schemes, the goal is to find compounds early or late, or also to indicate the phase transition. Some chemical reactions can also be added to the writing on the sig
n bow; eg the addition of water, heat, illumination, catalysis, etc.. Also, some minor products can be placed below the arrow.
An example of organic reactions: oxidation of ketones into esters with acid peroksikarboksilat
An example of organic reactions: oxidation of ketones into esters with acid peroksikarboksilat
Retrosintetik analysis can be used to design a complex synthesis reaction. The analysis starts from the products, for example by breaking chemical bonds are chosen to be the new reagents. Special arrows (⇒) is used in retro reactions.
Elementary reaction
Elementary reaction is the reaction of the simplest solution and the result of this reaction has no byproducts. Most reactions have been found at this time is the development of the emergence of elementary reactions in parallel or sequentially. An elementary reaction usually consists of only a few molecules, usually only one or two, because it is unlikely for many molecules join together.
Azobenzena isomerization induced by light (hν) or heat (Δ)
The most important reaction is an elementary reaction and the reaction unimolekuler bimolekuler. Reaction unimolekuler consists of only one molecule formed from the transformation or diasosiasi one or more other molecules. Some of these reactions require energy from light or heat. An example of unimolekuler reaction is cis-trans isomerization, in which a compound cis form will turn into a form of trance.
In the dissociation reaction, a bond in a molecule is split into two fragments of molecules. This solution can be homolitik or heterolitik. In solving homolitik, the bond will be split so that each product still has one electron to become neutral radicals. In solving heterolitik, both electrons of the chemical bond will remain one of its products, so it will produce charged ions. Dissociation reactions play an important role in the chain reaction, such as for example hydrogen-oxygen or polymerization reactions.
Disoasi of AB molecules into fragments A and B
In bimolecular reactions, two molecules will react with each other and bertabreakan. The results of the reaction is called chemical synthesis or an addition reaction.
Another possible reaction is part of a molecular switch to other molecules. The reaction of this type, for example, is a redox and acid-base reactions. In the redox reaction that moving particles are electrons, whereas the acid-base reactions are proton moving. The reaction is also called metathesis reactions.
NaCl (aq) + AgNO3 (aq) → NaNO3 (aq) + AgCl (s)
Azobenzena isomerization induced by light (hν) or heat (Δ)
Azobenzena isomerization induced by light (hν) or heat (Δ)
Chemical reactions can be determined by the laws of thermodynamics. The reaction can occur by itself when the compound is exergonic or energy release. The resulting free energy reaction consists of two massive thermodynamic enthalpy and entropy are
G: free energy, H: enthalpy, T: temperature, S: entropy, Δ: difference
Exothermic reaction occurs when ΔH is negative and energy is released. Examples of exothermic reactions are precipitation and crystallization, in which the solids are formed from gases or liquids. In contrast, in endothermic reactions, heat is taken from the environment. This can be done by increasing the entropy of the system. Because of entropy increase is directly proportional to its temperature, then most endothermic reaction carried out at high temperatures. In contrast, most of the exothermic reaction carried out at low temperature. Changes in temperature can sometimes change the course of the reaction, such as for example the Boudouard reaction:
The reaction between carbon dioxide and carbon to form carbon monoxide is endothermic at temperatures above 800 ° C and becomes exothermic reaction if the temperature is below this temperature
The reaction can also be determined by the energy that causes a change in entropy, volume, and chemical potential.
U: energy, S: entropy, p: pressure, μ: chemical potential, n: number of molecules, d: small change sign means
Grouping chemical reaction
The diversity of chemical reactions and approaches taken in the study resulted in many ways to classify these reactions, which often overlap. Below are examples of classification of chemical reactions that are normally used.
Four basic reaction
In direct combination or synthesis reaction, two or more simple compounds combine to form a new, more complex compound. Two or more reactants react to produce a product that is also one way to find out if it is the synthesis reaction. An example of this is the reaction of hydrogen gas with oxygen gas combine the result is water.
Another example is nitrogen gas combine with hydrogen gas to form ammonia, by the equation:
N2 + 3 H2 → 2 NH3
Decomposition reaction is the opposite of analysis or synthesis reactions. A more complex compounds are broken down into simpler compounds.
Examples are water molecules are split into hydrogen gas and oxygen gas, with the equation:
2 H2O → 2 H2 + O2
Single replacement
In a single replacement or substitution reaction, a single element of a single element replaces another in a compound. Examples are sodium metal reacts with hydrochloric acid will produce sodium chloride or table salt, the reaction persamaaan:
2 Na (s) + 2 HCl (aq) → 2 NaCl (aq) + H2 (g)
Replacement double
In a double replacement reaction, two ionic compounds or bond mutual change to a different form new compounds. [15] This occurs when the cations and anions of two different compounds each move, and form two new compounds. The general formula of this reaction is:
AB + CD → AD + CB
An example of a double replacement reaction is lead (II) nitrate reacts with potassium iodide to form lead (II) iodide and potassium nitrate, with the equation:
Pb (NO3) 2 + 2 KI → PbI2 + 2 KNO3
Another example is sodium chloride (table salt) reacts with silver nitrate to form sodium nitrate and silver chloride, the reaction equation:
NaCl (aq) + AgNO3 (aq) → NaNO3 (aq) + AgCl (s)
Oxidation and reduction
Illustration of a redox reaction (oxidation reduction)
The two parts of a redox reaction
Redox reactions can be understood as the transfer of electrons from one compound (called a reducing agent) to another compound (called oxidants). In this process, one will be oxidized compounds and other compounds are reduced, therefore called redox. Oxidation itself is understood as an increase in oxidation and reduction is a decrease in oxidation. In practice, the transfer of electrons will always change the oxidation number, but many of the reactions were classified as redox reactions despite the fact that no electrons are moved (such as those involving covalent bonds).
Examples of redox reactions are:
2 S2O32-(aq) + I2 (aq) → S4O62-(aq) + 2 I-(aq)
Which I2 is reduced to I-and S2O32-(thiosulfate anion) is oxidized into S4O62-.
To determine which reactant will be a reducing agent and which will be oxidized to unknown agents of electronegativity elements. Elements that have a low electronegativity value, like most metals, it will easily give their electrons and oxidize – this element into the reductant. Conversely, many ions have a high oxidation state, such as H2O2, MnO4-, CrO3, Cr2O72-, OsO4) can have one or more extra electrons, so-called oxidants.
The number of electrons that are given or received in the redox reaction can be determined from the configuration of the reactant element elektronn. Each element will try to make the same electron configuration as the noble gas configuration element. Alkali metals and halogens will give and accept one electron. Elements of the natural gas itself is not chemically active.
One important part of redox reactions are the electrochemical reactions, where the electrons from the power source is used as the reductant. This reaction is important for the manufacture of chemical elements, such as chlorine or aluminum. The reverse process where the redox reaction is used to generate electricity and also there is the principle used in the battery.
Acid-base reactions

Acid-base reaction is the reaction that donates a proton from a molecule of acid to alkaline molecules. Here, acids act as proton donors and bases act as a proton acceptor.
Acid-base reaction, HA: acid, B: Bases, A-: conjugated base, HB +: conjugated acid
The results of this proton transfer is the conjugate acid and conjugate base. Reaction equilibrium (back and forth) also exist, and therefore acid / alkaline and acid / conjugate base is always in equilibrium. The reaction equilibrium is characterized by the presence of acids and bases diasosiasi constants (Ka and Kb) of each substance. A special reaction of the acid-base reaction is the neutralization of acids and bases in which the same amount of salt will form a neutral nature.
Acid-base reactions have different definitions depending on the acid-base concepts used. Some of the most common definitions are:
Definition Arrhenius: acid dissociates in water releasing H3O + ions; bases dissociate in water releasing OH-ions.
Brønsted-Lowry definition: Acids are proton donors (H +) donors; bases is the recipient (acceptor) proton. Arrhenius definition covers
Lewis definition: Acids are electron pair acceptors; bases are electron pair donors. This definition covers the Brønsted-Lowry definition.
Precipitation is the formation reaction of solids (sediment) in a solution as a result of chemical reactions. Precipitation is usually formed when the concentration of the dissolved ions have reached the solubility limit and the result is a form of salt. This reaction can be accelerated by adding a reducing agent or solvent precipitation. Rapid precipitation reaction will produce microcrystalline residue and slow process that will result in a single crystal. Single crystals can also be obtained from recrystallization from microcrystalline salts.
Reactions on solid
The reaction can take place between two solids. However, since the rate of diffusion in solids is very low, the chemical reactions that take place happen very slowly. The reaction can be accelerated by increasing the temperature so it will break the reactants, so that the contact surface area becomes larger.
Photochemical Reaction
In the Paterno-Buchi reaction, an excited carbonyl group into olefin will diamahkan not excited, and produce oksetan.
In photochemical reactions, atoms and molecules absorb energy (photons) from the light and convert it into excitation. Atoms and molecules and can release energy by breaking chemical bonds, the yield radicals. Reaction ang included in photochemical reactions include hydrogen-oxygen reactions, radical polymerization, chain reactions and rearrangement reactions.
Many important processes using photochemical. The most common example is photosynthesis, which plants use solar energy to convert carbon dioxide and water into glucose and oxygen as a byproduct. Humans rely on photochemistry in the formation of vitamin D, and visual perception resulting from the photochemical reaction in rhodopsin. In fireflies, an enzyme in the abdomen catalyzes a reaction that produces bioluminesensi. Many photochemical reactions, such as ozone formation, occur in the Earth’s atmosphere, which is part of the atmospheric chemistry.
Energy schematic diagram showing the effect of giving a catalyst in an endothermic chemical reaction. Presence of a catalyst will speed up the reaction by lowering the activation energy. The end result will be the same as the reaction without catalyst.
In catalysis, the reaction does not take place spontaneously, but through a third substance known as catalyst. Unlike other reagents that participate in the chemical reaction, the catalyst does not take part in the reaction itself, but to inhibit, shut down, or destroyed by secondary processes. The catalyst can be used in different phases (heterogeneous catalysts) and in the same phase (homogeneous catalyst) as the reactants. The function of the catalyst is accelerating the reaction – chemicals that slow the reaction are called inhibitors. Substances that increase the activity of catalysts are called promoters, and substances called catalysts deadly poison catalysts. A chemical reaction that should not take place because the activation energy is too high, it could be underway by the presence of this catalyst.
Heterogeneous catalysts are usually solids and powder form in order to maximize the surface area that reacted. Substances that are important in heterogeneous catalysis include platinum group metals and other transition metals. These substances are commonly used in hydrogenation, catalytic formation and synthesis of chemical compounds such as nitric acid and ammonia. Acid is an example of a homogeneous catalyst, they increase nukleofilitas of carbonyl. The advantages of homogeneous catalysts is easy to be mixed with the reactant, but the drawback is difficult to be separated from the final product. Therefore, heterogeneous catalysts are preferred in many industrial processes.
Reactions in organic chemistry
In organic chemistry, many reactions that can occur involving covalent bonds between carbon atoms and heteroatoms such as oxygen, nitrogen, or other halogen atoms. Some more specific reactions are described below.
In a substitution reaction, a functional group in a chemical compound is replaced by other functional groups. This reaction can be divided into several subtypes, namely nucleophilic, electrophilic substitution, or radical substitution.
SN1 mechanism
SN2 mechanism
In the first type, a nucleophile, an atom or molecule that has an excess of electrons that are negatively charged, will replace another atom or other parts of the molecule “substrate”. Nucleophile electron pair will unite to form a new bond with the substrate, while the group will take off along with a pair of electrons. Nucleophile itself can be neutral or positively charged, whereas the substrate is usually positively charged or neutral. Examples of nucleophiles are hydroxide ion, alkoxides, amines and halides. Such reactions are usually found in aliphatic hydrocarbons, and rarely found in aromatic hydrocarbons. Aromatic hydrocarbons having a steeper electron density and could only hold a nucleophilic aromatic substitution only with towing force powerful electron. Nucleophilic substitution can take place through two mechanisms, SN1 and SN2 reactions. According to its name, the S stands for substitution, N stands for nucleophilic dai, and, and the numbers indicate the order kinetic reaction, unimolekuler or bimolekuler.
3 stages in SN2 reactions. Nucleophile green and red loose clusters
SN2 reaction causes inversion stereo (Walden inversion)
SN1 reaction takes place in two stages. The first phase, the group will take off and form a carbocation. This stage will be followed by a very rapid reaction with the nucleophile.
In the SN2 mechanism, a nucleophile to form a transition phase with molecules that are terlekang off. These two mechanisms differ in stereochemistry results. SN1 reaction produces non-stereospecific addition and does not produce a chiral center, but rather in the form of geometrical isomers (cis / trans). In contrast, inversion Warden who observed the SN2 mechanism.
Electrophilic substitution is the opposite of nucleophilic substitution in which the atoms or molecules of a release, or elektrofilnya, has a low electron density thus positively charged. Usually this is the electrophile carbon atom of the carbonyl groups, carbocations or sulfur or nitronium cations. This reaction takes place in the course of aromatic hydrocarbons, so-called electrophilic aromatic substitution. Electrophile attack would create a complex called σ-compleks, a phase transition in which the aromatic system is lost. Then, loose clusters (typically protons), will separate and the nature kearomatikannya back. Another alternative to aromatic substitution is electrophilic aliphatic substitution. Substitution is similar to electrophilic aromatic substitution and also has two major types, namely SE1 and SE2
SN1 mechanism
SN1 mechanism
SN2 mechanism
SN2 mechanism
The mechanism of electrophilic aromatic substitution
The mechanism of electrophilic aromatic substitution
Addition and elimination
Addition and elimination partner is a reaction that converts the number of substituents on the carbon atoms, and form a covalent bond. Double and triple bonds can be produced by eliminating a suitable loose clusters. As the nucleophilic substitution, there are several possible reaction mechanisms. In the E1 mechanism, first remove loose clusters and form a carbocation. Furthermore, the formation of a double bond occurs through the elimination of a proton (deprotonation). In E1cb mechanism, reverse the order of release: proton eliminated first. In this mechanism there should be the involvement of a base. [35] in the elimination reaction E1 and E1cb always competes with SN1 substitution reaction conditions because they have the same condition.
elimination E1
elimination E1
elimination E1cb
elimination E1cb
elimination E2
elimination E2
E2 mechanism also requires a base. However, the change of position of the group off the bases and elimination take place simultaneously and produce no ionic intermediates. In contrast to the E1 eliminations, different stereochemical configurations can be generated in the reaction with E2 mechanism bases will be more favored for elimination of protons that are in a position to force the anti-loose. Therefore, the reaction conditions and reagents were similar, E2 elimination always compete with SN2 substitution.
Electrophilic addition of hydrogen bromide
The opposite of elimination reaction is an addition reaction. In addition reactions, double bonds or triple converted to a single bond. Similar to the substitution reactions, there are several types of adducts were indistinguishable from particles mengadisi. For example, the electrophilic addition of hydrogen bromide, an electrophile (proton) will replace the double bond to form carbocation, and then reacts with the nucleophile (bromine). Carbocation can form a bond depends on the group attached at the end. Configurations can be predicted more accurately with the Markovnikov rule. Markovnikov rule says: “In addition sebuuah heterolitik of polar molecules in the alkene or alkyne, atoms that have a large electronegativity, it will be bound to the carbon atom with fewer hydrogen atoms.”
Other organic chemical reaction
Orbital overlap in a Diels-Alder reaction
In the rearrangement reaction, the carbon skeleton of a molecule rearranged to form isomeric structure of the original molecule. The reaction was included with [reaction sigmatropik]] such as the Wagner-Meerwein rearrangement, where hydrogen, alkyl, or aryl place moving from one carbon atom to another carbon atom. Most of the rearrangement reaction is breaking and formation of new carbon-carbon bonds. Another example of this reaction is the rearrangement cope.
another reaction
Isomerization, which undergo chemical rearrangement of the structure without a change in the composition of the atom
Burning, is a kind of redox reaction in which materials can ignite join elements oxidant, usually oxygen, to generate heat and form oxidized products. Combustion term usually used to refer only to the large-scale oxidation of whole molecules. Controlled oxidation of only one single functional group is not included in the combustion process.
C10H8 + 12 O2 → 10 CO2 + 4 H2O
CH2S + 6 F2 → CF4 + 2 HF + SF6
Disproportionation, with one reactant form two different types of products only in the state of oxidation.
SN2 → Sn 2 + + + SN4


  1. Rinaldi Prasetia
    The number of electrons that are given or received in the redox reaction can be determined from the configuration of the reactant element elektronn. Each element will try to make the same electron configuration as the noble gas configuration element. Alkali metals and halogens will give and accept one electron. Elements of the natural gas itself is not chemically active.
    why elements of the natural gas is chemically inactive?
  2. noble gas elements in the actual active but its activity level is low, and therefore most people say that the noble gases unsusr off.
    it is because the state of the electrons in the outer shell of the noble gas elements are likely to have been achieved stability.