NCERT Solution for Class 10 Science Chapter 1
Chemical Reactions and Equations
Exercises Questions
Page No-15
Questions No-11
Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
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In decomposition reaction, a single reactant breaks down into two or more simpler product, while in combination reaction two or more reactant combine to form a single product. Therefore decomposition and combination reaction are opposite.
Example of decomposition :
(i) 2FeSO4(s) —Heat→ Fe2O3(s) + SO2(g) + SO3(g)
Ferrous sulphate Ferric oxide
(ii) CaCO3(s) —Heat→ CaO(s) + Co2(g)
Lime stone Quick lime
Example of combination :
(i) CaO(s) + CO2(g) → CaCO3(s)
Quick lime Carbon dioxide Lime stone
(ii) Burning of coal →
C(s) + O2(g) → CO2(g)
In a combination reaction two or more substances are combined to form new substance while in the decomposition reaction one substance decomposes into two or more substances. Hence, the decomposition reactions are called opposite of combination reactions.
Example of decomposition :
(i) 2FeSO4(s) —Heat→ Fe2O3(s) + SO2(g) + SO3(g)
Example of combination :
(i) CaO(s) + CO2(g) → CaCO3(s)