Decomposition reaction refers to the breakdown of compounds into two or more of its constituents. In general, the decomposition reaction can be represented by AB → A + B. Not all decomposition reactions are redox reactions. The opposite of decomposition is synthesis, where a new compound is formed by the reaction of two or more reactants. The decomposition reaction requires energy in the form of heat, electricity or light to break the bonds. Decomposition reactions can be classified into thermal, electrolytic and photolytic decomposition.
1. CO2 obtained by the complete decomposition of 20 g CaCO3 at STP is
(a) 4.48 l
(b) 2.24 l
(c) 44.8 l
(d) 48.4 l
Answer: (a)
2. Decomposition of hydrogen peroxide to give H2O + O2 is an example of
(a) reduction
(b) oxidation
(c) both (a) and (b)
(d) none of the above
Answer: (c)
3. The reaction 2Pb(NO3)2 → 2PbO + 4NO2 + O2 is a type of _______reaction.
(a) displacement
(b) double decomposition
(c) decomposition
(d) none of the above
Answer: (c)
4. On passing current to an acidified water we get hydrogen and oxygen. This is a type of
(a) oxidation reaction
(b) thermal decomposition
(c) electrolysis
(d) none of the above
Answer: (c)
5. The correct expression for decomposition of silver chloride to silver and chlorine is
(a) AgCl2(s) → Ag(s) + 2Cl(g)
(b) 2AgCl(s)→ 2Ag(s) + Cl2(g)
(c) AgCl2(s) → Ag(s) + Cl2(g)
(d) AgCl(s) → Ag(s) + Cl(g)
Answer: (b)
6. A reaction where two compounds exchange their atoms to form new compounds
(a) decomposition
(b) double displacement
(c) displacement
(d) synthesis
Answer: (b)
7. The decomposition of silver chloride occurs by
(a) heat
(b) sunlight
(c) water
(d) electricity
Answer: (b)
8. How many moles of sodium carbonate is formed on decomposition of 0.2 moles of sodium bicarbonate?
(a) 0.1
(b) 0.2
(c) 0.05
(d) 0.025
Answer: (a)
9. Find out the volume of CO2 liberated after heating 9.85 g of BaCO3 at STP.
(a) 2.06 l
(b) 2.12 l
(c) 1.12 l
(d) 4.84 l
Answer: (c)
10. Ferrous sulphate on heating gives reddish-brown residue of ferric oxide. This is due to
(a) decomposition
(b) displacement
(c) combination
(d) none of the above
Answer: (a)
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