Chemical reaction

Chemical reaction, a process in which one or more substances, the reactants, are converted to one or more different substances, the products. Substances are either chemical elements or compounds. A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products.

Essentials of a chemical equation

1.  It should represent the chemical reaction which is practically possible.
2. It should be balanced that is the total number of atoms present in the reactant side must be equal to the total number of atoms present in the product side.
3. All the elementary of gases such as hydrogen, oxygen, Nitrogen etc should be diatomic form.

Significance of chemical reaction

Calcium carbonate reacts with dilute hydrochloric acid to give calcium chloride water and CO2. This chemical reaction can be written as:

CaC03 + dil 2HCL → CaCl2 + H20 + CO2

40+12+48   2(1+35.5)    40+71    2+16   12+32

=100         =73          =111      =18     =44

1. Qualitatively this equation says that calcium carbonate reacts with hydrochloric acid to give calcium chloride, water and carbon dioxide. But qualitatively the 100 parts by weight of CaC03 reacts with 73 parts of HCl by weight to give 111 parts by weight of CaCl2. 18 parts by weight of water and 44 parts by weight of CO2.
2. This equation also says that one molecule of calcium carbonate reacts with two molecules of HCl to give one molecule each of calcium chloride, water and carbon dioxide.
3. This equation also says that one mole of CaC03 reacts with two moles of HCl to give one mole each of CaCl2, H2O and CO2.

Limitations of the chemical equation:

1. It does not mention the state of the substances. So (s) for solid, (l) for liquid, (g) for gas and (vap) for vapour may be added.
2. The reaction may or may not be complete. The equation does not reveal it.
3. It does not give any information regarding the speed of the reaction.
4. It does not give the concentration of the substances. In some cases, terms like diluted and concentrated may be added.
5. It does not give the conditions of temperature, pressure, catalyst, etc. This is overcome by mentioning these above or below the arrow.