Question

The enthalpy change for a certain reaction at 300 K is -15.0 Kcal mol${}^{-1}$. The entropy change under these conditions is -7.2 cal K${}^{-1}$ mol${}^{-1}$. The free energy change for the reaction and its spontaneous/nonspontaneous character will be:

• A. -12.84 Kcal mol${}^{-1}$, spontaneous
• B. -12.16 Kcal mol${}^{-1}$, spontaneous
• C. 12.84 Kcal mol${}^{-1}$, non spontaneous
• D. 12.0 Kcal mol${}^{-1}$, spontaneous

Answer 1

The correct option is A -12.84 Kcal mol${}^{-1}$, spontaneous

The change in Gibbs free energy associated with a chemical reaction is a useful indicator of whether the reaction will proceed spontaneously. When the free energy is negative, the reaction will be spontaneous.

$\Delta H=-150$ Kcal mol${}^{-1}$

$\Delta S=-7.2$ cal mol${}^{-1}$ K ${}^{-1}$

Gibb's free energy equation is

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

$\Delta G=(-15\times 1000)-300\times (-7.2)$

$\Delta G=-12.8$ Kcal$

Above reaction will be spontaneous as the free energy is negative.

Hence, the correct option is $\text{A}$