Consider the following reaction : 2A(g) + B(g) 2D(g) U = −10 kJ mol-1 and S = −44 J K-1 at 298 K. Identify the correct option with G for the reaction and spontaneity of the reaction at 298 K. (Given : R = 8.31 J mol-1 K-1)
- +0.63568 kJ mol-1, non-spontaneous
- −0.63568 kJ mol-1, spontaneous
- −1.635 kJ mol-1, spontaneous
- +1.635 kJ mol-1, non-spontaneous
Answer
(1) +0.63568 kJ mol-1, non-spontaneous
Solution
ng = 2 − (2 + 1) = −1
H = U + ngRT
⇒ H = -10 + (-1)(8.31)(298)1000
⇒ H = -10 - 2.476 = -12.476 kJ mol-1
G = H - T S
⇒ G = -12.476 - 298 (-0.044)
⇒ G = -12.476 + 13.112 = +0.636 kJ mol-1 ≈ +0.63568 kJ mol-1
∵ G > 0 ∴ the reaction is non-spontaneous at 298 K.
Answer: (1)