Chemistry - Thermodynamics - II Question with Solution | TestHub

For the reaction:

$$CO(g)+H_{2}O(g)\to C{O}_2(g)+H_2(g)$$

First, calculate the enthalpy change:

$${\Delta }_{r}H=[(-390)+0]-[(-110)+(-240)]=-390+350=-40kJmo{l}^{-1}$$

Hence, (A) is correct.

Now, the entropy change at 400 K:

$${\Delta }_{r}S=(50+45)-(45+55)=-5J{K}^{-1}mo{l}^{-1}$$

So, option (B) is wrong.

At 400 K:

$${\Delta }_{r}G={\Delta }_{r}H-T{\Delta }_{r}S$$

$${\Delta }_{r}G=-40-400(-5\times 10^{-3})=-40+2=-38kJmo{l}^{-1}$$

Therefore, (C) is incorrect.

At 450 K:

$${\Delta }_{r}G=-40-450(-5\times 10^{-3})=-40+2.25=-37.75kJmo{l}^{-1}$$

Thus, (D) is also incorrect.