Question

In which case change in entropy is negative?

• A. Evaporation of water
• B. Expansion of a gas at constant temperature
• C. Sublimation of solid to gas
• D. $2H\left(g\right)\to H_2\left(g\right)$

Answer 1

Answer: (D)

$2H\left(g\right)\to H_2\left(g\right)$

$\Rightarrow$ $H_{2}O\left(\ell \right)\rightleftharpoons H_{2}O\left(v\right),\Delta S>O$

$\Rightarrow$ Expansion of gas at a constant temperature, $\Delta S>0$

$\Rightarrow$ Sublimation of solid to gas, $\Delta S>0$

$\Rightarrow 2H\left(g\right)⟶H_2\left(g\right),\Delta S<0(\because \Delta n_g<0)$