A chemical equation can be made more informative by adding additional information to the chemical equation. This is done as follows:
(i) Reaction conditions:
The information regarding temperature, pressure, and catalyst etc. is provided above the arrow (→ or =) separating the reactants and products.
For example, nitrogen and hydrogen react to form ammonia under the condition; temperature =450°C, pressure =200-900 atm, and in the presence of a catalyst (a mixture of an iron and molybdenum).
(ii) Physical state of reactants and products:
Information regarding the physical states of the reactants and precuts, can be provided by using the letters(s), (l), (g) and (aq) for solid, liquid, gas and a solution in water, respectively, at the end of the formula of the substance involved. For example, solid sodium metal reacts with water atomic room temperature to produce hydrogen gas, and a solution of sodium hydroxide in water. Then , the complete chemical equation is..
ADVERTISEMENTS:
2Na(s) + 2H2O (l) → 2NaOH (aq) + H2 (g)
(iii) Heat absorbed or evolved:
Chemical reactions proceed with the evolution or absorption of heat. The reactions in which heat is absorbed are called endothermic reactions. The reactions in which heat is given out are called exothermic reactions. This information is provided by adding a heat term only the product-side (right hand side) of the chemical equation. For example,
(a) When carbon is burnt in air (or oxygen) heat is evolved. Then, the chemical equation is written as,
C(s) + O2 (g) → CO2 (g) + Heat (393 kJ)
ADVERTISEMENTS:
The reactions with +Heat term on the product side are called exothermic reactions, while those with –Heat term on the product side are called endothermic reactions.
(iv) Concentration of the reactants and products:
This information is added to the chemical equation by adding the word dil. (for dilute) or conc.(for concentrated) before the formulae of the reactants and products. For example, in the reaction between zinc and dilute sulphuric acid, the term dil. is added before the formulae of sulphuric acid.
Zn(s) + dil. H2SO4(aq) → ZnSO4(aq) + H2(g)
(v) Rate of reaction:
This information is not commonly added to the chemical equation. Sometimes, however, the term fast or slow may be added over the arrow, if the reaction is fast or slow. For example, the reaction between HCl and NaOH in solution is a fast reaction. So,
HCl (aq) + NaOH(aq) fast NaCl(aq) + H2O(l)