Question

Which of the following are exothermic processes?

• A. (i) and (ii)
• B. (ii) and (iii)
• C. (i) and (iv)
• D. (iii) and (iv)

Answer 1

The correct option is A

(i) and (ii)

The explanation for the correct option:

(A) (i) and (ii)

Exothermic Process

Any reaction where heat is released during the reaction process is called an exothermic reaction.

(i) Heat is released during the reaction of water$\left({\mathrm{H}}_2\mathrm{O}\right)$ with quick lime$\left(\mathrm{CaO}\right)$ so it is an exothermic process along with the production of slaked lime$\left(\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\right)$.

$\mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to \mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)+\mathrm{Heat}$

(ii) Heat is also released when acids (let's say $\mathrm{HA}$) are diluted along with the production of hydronium ions and conjugate bases (in this reaction ${\mathrm{A}}^{-}$).

$\mathrm{HA}\left(\mathrm{aq}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to {\mathrm{H}}_3{\mathrm{O}}^{+}+{\mathrm{A}}^{-}+\mathrm{Heat}$

Explanation of incorrect options:

(iii) For evaporation of water, heat is absorbed so it is not exothermic in nature.

${\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+\mathrm{Heat}\to {\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)$

(iv) Sublimation of camphor$\left({\mathrm{C}}_{10}{\mathrm{H}}_{16}\mathrm{O}\right)$ occurs when heat is absorbed so it is not exothermic.

${\mathrm{C}}_{10}{\mathrm{H}}_{16}\mathrm{O}\left(\mathrm{s}\right)+\mathrm{Heat}\to {\mathrm{C}}_{10}{\mathrm{H}}_{16}\mathrm{O}\left(\mathrm{g}\right)$

Therefore, reactions (i) and (ii) are exothermic, and hence, option (A) is the correct option.