Question

For a chemical reaction the values of $\Delta H$ and $\Delta S$ at 400 K are -10 K cal mol${}^{-1}$ and 20 cal. deg${}^{-1}$ mol${}^{-1}$ respectively. Calculate the value of $\Delta G$ of the reaction.

Answer 1

$\Delta H$ and $\Delta S$ values of a reaction at 400 K are -10 K cal mol${}^{-1}$ and 20 cal deg${}^{-1}$ mole${}^{-1}$ respectively. Calculate $\Delta G$ value.
$\Delta S$ = enthalpy change = - 10 K cal mol${}^{-1}$
$\Delta S$ = entropy change = 20 cal deg${}^{-1}$ mol${}^{-1}$
T = 400 K
$\Delta G=\Delta H-T\Delta S$
$=-10000calmo{l}^{-1}-(400\times 20)calde{g}^{-1}mo{l}^{-1}$
$=-18,000calde{g}^{-1}mo{l}^{-1}$
$=18Kcalde{g}^{-1}mo{l}^{-1}$