Question

In which of the following processes, entropy increases?
(I) A liquid crystallizes into a solid
(II) Temperature of a crystalline solid is raised from $0 \,K$ to $115 \,K$
(III) $2NaHCO_{3(s)} \to Na_{2}CO_{3(s)}+CO_{2(g)}+H_{2}O_{(g)}$
(IV) $H_{2(g)} \to 2H_{(g)}$

• A. Only (I)
• B. (I) and (II)
• C. (II), (III) and (IV)
• D. (I) and (IV)

Answer 1

Answer: (C)

(I) After freezing, the molecules attain an ordered state and therefore, entropy decreases
(II) At $0 \,K$ , the constituent particles are static and entropy is minimum. If temperature is raised to $115 \,K$, these begin to move and oscillate about their equilibrium positions in the lattice and system becomes more disordered, therefore entropy increases
(III) In the reaction,
$2NaHCO_{3(s)} \to Na_{2}CO_{3(s)}+CO_{2(g)}+H_{2}O_{(g)}$
the number of gaseous components are increasing hence the entropy of system will increase
(IV) $H_{2(g)} \to 2H_{(g)}$
In this decomposition, number of particles increase therefore, the randomness and entropy will also increase