Enthalpy, Helmholtz and Gibbs free energies
Thermodynamic potentials (UG) · Physics
Gas piston lab
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Study notes
A reaction at 298 K and 1 atm has delta_H = -120 kJ/mol and delta_S = -150 J/(mol K). (a) Compute delta_G. (b) Is the reaction spontaneous? (c) Above what temperature does it become non-spontaneous? Solution: (a) delta_G = delta_H - T delta_S = -120,000 - (298)(-150) = -120,000 + 44,700 = -75,300 J/mol = -75.3 kJ/mol. (b) delta_G < 0, so yes, spontaneous at 298 K. (c) Set delta_G = 0: T = delta_H/delta_S = (-120,000)/(-150) = 800 K; above 800 K the -T delta_S term wins and delta_G > 0.