State two characteristics of chemical reactions.

Two characteristics of chemical reaction are given below:

1. Evolution of gas : In many chemical reactions, one of the products is a gas.
   Example- When zinc reacts with dilute sulphuric acid, hydrogen gas is evolved with an effervescence.

2. Change of colour : Certain chemical reactions are characterised by a change in the colour of the reactants.
   Example- When a few pieces of iron are dropped into a blue coloured copper sulphate solution, the blue colour of the solution fades and eventually turns into light green.