Thermodynamics and Thermochemistry - Result Question 12
12. The standard reaction Gibbs energy for a chemical reaction at an absolute temperature $T$ is given by, $\Delta _r G^{\mathbf{o}}=A-B T$
Where $A$ and $B$ are non-zero constants.
Which of the following is true about this reaction?
(2019 Main, 11 Jan II)
(a) Endothermic if, $A < 0$ and $B > 0$
(b) Exothermic if, $B < 0$
(c) Exothermic if, $A > 0$ and $B < 0$
(d) Endothermic if, $A > 0$
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Answer:
Correct Answer: 12. (d)
Solution:
According to Gibb’s Helmholtz equation,
$ \begin{aligned} & \Delta _r G^{\circ} =\Delta _r H^{\circ}-T \Delta _r S^{\circ} \\ \text { Given, } & \Delta _r G^{\circ} =A-B T \end{aligned} $
On comparing above two equations, we get,
$ A=\Delta H^{\circ} \text { and } \Delta S^{\circ}=B $
We know that, if $\Delta H^{\circ}$ is negative, reaction is exothermic and when it is positive, reaction is endothermic.
$\therefore$ If $A>0$, i.e. positive, reaction is endothermic.
BETA
