A reaction has a ΔH value of + 120 kJ and a ΔS value of - 42 J/K. At which of the following temperatures is the reaction spontaneous (meaning ΔG is negative) ?

the reaction is spontaneous at T > 2900 K

Explanation:

ΔG = ΔH - TΔS

∴ ΔH = + 120 KJ

∴ ΔS = (-42 J/K) * (KJ/1000 J) = - 0.042 KJ/K

∴ ΔG < 0 ⇒ the reaction is spontaneous

⇒ at T = 2900 K:

⇒ ΔG = 120 - (2900) (-0.042) = 120 - 121.8 = - 1.8 KJ < 0