Question

The Gibbs energy change accompanying a given process is -85.77 kJ mol${}^{-1}$ at 25${}^o$C and -83.68 kJ mol${}^{-1}$ at 35${}^o$C. The heat of reaction of process at 30${}^o$C is:

• A. -148.05 kJ mol${}^{-1}$
• B. -138.15 kJ mol${}^{-1}$
• C. -168.25 kJ mol${}^{-1}$
• D. none of these

Answer 1

The correct option is A -148.05 kJ mol${}^{-1}$

Assume that the enthalpy change and the entropy change are not affected by the temperature change of about ${10}^{o}C$.

$\Delta G=\Delta H-T\Delta S$

$-85770=\Delta H-298\times \Delta S$...... (1)

$-83680=\Delta H-308\Delta S$......(2)

From (1) $\Delta S=\frac{\Delta H+85770}{298}$......(3)

Substitute (3) into (2)

$-83860=\Delta H-\frac{308}{298}(\Delta H+85770)$

$\Delta H=-148052kJ/mol=-148.05J/mol$