Q8 of 39 Page 1

Describe and activity to show decomposition reaction in which light is used to decompose a reactant. Write chemical equation of the reaction and state its one use. (2012)

Take about 2 g silver chloride in a china dish. It is first white in colour. Now place this china dish in sunlight for some time. After some time it is observed that white silver chloride turns grey. This is due to the decomposition of silver chloride into silver and chlorine by light.

2AgCl 2Ag (s) + Cl2 (g)


Silver bromide also decomposed to silver and bromine by light.


2AgBr 2Ag (s) + Br2 (g)


Use: The reaction is used in black and white photography.


More from this chapter

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17

Identify the type of each of the following reactions:

a. A reaction in which a single product is formed from two or more reactants.


b. The reaction mixture becomes warm.


c. An insoluble substance is formed. (CBSE 2009)

 7

(a) Give an example for a combination reaction which is exothermic.

(B) Identify the oxidising agent, reducing agent in the following reaction: H2S + Cl2 → 2HCl + S


(c) Name the phenomenon due to which the taste and smell of oil food changes when kept for a long time open. Suggest one method to prevent it. (2012)


 9

(a) What is meant by balanced chemical equation? Why chemical equations are balanced?

(b) Balance the chemical equation given below:


Al2O3 + NaOH → NaAlO2 + H2O (2013)


 10

Write balanced chemical equations for the following reactions: (2013)

(a) dilute sulphuric acid reacts with aluminium powder


(b) dilute hydrochloric acid reacts with sodium carbonate


(c) Carbon dioxide is passed through lime water.