Question

For the reaction given below the values of standard Gibbs free energy of formation at 298 K are given. What is the nature of the reaction?

$I_{2} + H_{2}S \rightarrow 2HI + S$

$\Delta G_{f}^{o}(HI) = 1.8kJmol^{- 1},\Delta G_{f}^{o}(H_{2}S) = 33.8kJmol^{- 1}$

• A. Non – spontaneous in forward direction
• B. Spontaneous in forward direction
• C. Spontaneous in backward direction
• D. Non – spontaneous in both forward and backward directions.

Answer 1

Answer: (B)

Spontaneous in forward direction

Answer 2

: $I_{2} + H_{2}S \rightarrow 2HI + S$

$\Delta G^{o} = \sum{G_{f}^{o}}_{products} - \sum{G_{f}^{o}}_{{Re}ac\tan ts}$

$\Delta G^{o} = (2 \times 1.8 + 0) - (0 + 33.8) = - 30.2kJ$

Hence, reaction is spontaneous in forward direction.