Question

A reaction has ΔH° = 100 kJ/mol and ΔS°=250 J/mol.K. Is the reaction spontaneous at room temperature? If not, under what temperature conditions will it become spontaneous?

Answer 1

$\Delta$H⁰ = 100KJ/mol and $\Delta$S⁰ = 250J/mol.K

Room temperature = 298K

$\Delta$ G⁰ = $\Delta$ H⁰ - T $\Delta$ S⁰

= 100 KJ/mol - 298K (250J/mol.K)($\frac{1KJ}{10³J}$ )

= 100 - 74.5 = 25 5 KJ

$\Delta$ G⁰ = + postive , the reaction is not spontaneous under room temperature at 298 K

Now we take temperature 410K

$\Delta$ G⁰ = 100KJ/mol - 410K (250J/mol.K)($\frac{1KJ}{10³J}$)

= 100 - 102.5 = - 2.5 KJ

$\Delta$ G⁰ = - negative , the reaction is spontaneous at 410K temperature.