Question

Find the temperature (in K) above which a reaction with a delta H of 123.0 kJ/mol and a delta S of 90.0 J/K×mol becomes spontaneous. Use four significant figures.
T=________K

Answer 1

We have the Gibbs- Helmholtz relation of free energy and enthalpy, entropy as

   delta G = delta H - T. delta S

and at equilibrium the delta G becomes zero.

For the given reaction both delta H and delta S are positive, it is entropy driven and becomes spontaneous at higher temperatures.( reaction is endo thermic.)

Let us find the temperature above which the given reaction becomes spontaneous as

      T= deltaH/ delta S

         = [123x1000J/mol] / [ 90J/K.mol]

       = 1366.66K

Thus above 1366.67 K the reaction becomes spontaneous.