First slide

Gibb's Helmholtz equation

Question

For a reaction the ΔS value is -20Jmol^–1k^-1. If the temperature is increased from 0°C to 25°C, the increase in the value of ΔG is (in J mol^–1) (Hint : use ΔG = ΔH –T ΔS)

Moderate

A

500
B

–500
C

0
D

14900

Solution

$\begin{array}{l} \Delta {G_1} = \Delta {H_1} - {T_1}\Delta S\\ \Delta {G_2} = \Delta {H_2} - {T_2}\Delta S \end{array}$
$\Delta {H_1} = \Delta {H_2}$ ( $\because$ the reaction is same)
$\begin{array}{l} Increase{\rm{ }}in{\rm{ }}\Delta G = \Delta {G_2} - \Delta {G_1}\\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = ({T_1} - {T_2})\Delta S\\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = (0 - 25)\Delta S = - 25( - 20)\\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = + 500J/mole \end{array}$

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