Rinaldi Prasetia

MID SEMESTER TEST

COURSE : BASIC CHEMISTRY I

NAME : RINALDI PRASETIA

NIM : RSA1C112011

  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.

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 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.

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:

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.

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.