For the isomerisation K -> T of a kinetic product K to the thermodynamic-looking isomer T, Delta H deg = -10.0 kJ mol^-1 and Delta S deg = -30.0 J mol^-1 K^-1 (both independent of temperature). Above which temperature does K become the major component of the equilibrium mixture?

JEE Advanced levelSingle correct optionDifficulty 3 of 3g3212

For the isomerisation $K T$ of a kinetic product K to the thermodynamic-looking isomer T, $Δ H^{\circ} = - 10.0 kJ mo l^{- 1}$ and $Δ S^{\circ} = - 30.0 J mo l^{- 1} K^{- 1}$ (both independent of temperature). Above which temperature does K become the major component of the equilibrium mixture?

Δ G^{\circ} = Δ H^{\circ} - T Δ S^{\circ} = - 10000 + 30.0 T

(J/mol). It is zero at

T = 10000/30.0 = 333.3

K. Above this temperature

Δ G^{\circ} > 0

, so K is favoured at equilibrium. Note:

333^{\circ} C

would be a confusion of scales.