Balance the following chemical equations: i. ii. .

4 A sample of water weed was placed in water and exposed to sunlight. Bubbles of a gas are seen on the surface of the leaves.
(i) Name the gas evolved.
(ii) Name the process taking place.
(iii) Write a balanced equation of reaction taking place. 5 Give balanced equations, wherever possible, or where this is not possible, explain the following by means of examples:
(i) A reaction which gives out heat.
(ii) A reaction which takes place with the help of sunlight.
(iii) A reaction which is brought about by electric current.
(iv) Reversible Reactions.
(v) A reaction with a solid and gas which produces heat. 7 Write the uses of decomposition reactions. 8 What are the characteristics of chemical reactions?