A
chemical equation is a shorthand description of a reaction
carried out in a laboratory or elsewhere. It gives the formulas
for all the reactants and products. For example
C + O2 ->CO2 ..... (1)
2H2 + O2 ->2H2O .......(2)
In a chemical reaction reactants are written on the left
and products are written on the right side of the arrow.
Arrow indicates conversion of reactant(s) into product(s).
In a chemical reaction atoms are neither created nor destroyed.
This is known as law of conservation of mass. A chemical
equation, therefore, should be consistent with this law.
Total number of atoms of each element must be the same in
the products and in the reactants. As shown in equation
(2) above two molecules (four atoms) of hydrogen react with
one molecule (two atoms) of oxygen and give two water molecules
in which there are four hydrogen atoms and two oxygen atoms.
Since number of atoms of the involved elements is equal
on both side of the arrow in the equation, we say the equation
is balanced. A balanced chemical equation is quite meaningful
in science (chemistry) as it gives a lots of information.
In order to make an equation more informative, we also indicate
the physical states of the reactants and products. We write
in parenthesis ‘s’ if the substance is solid,
‘l’ if the substance is liquid and ‘g’
if the substance is a gas. Accordingly, equation (1) and
(2) can be written as,
C (s) + O2 (g) ->CO2 (g)
2H2 (g) + O2 (g) ->2H2O
(l)
