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# Free Gibbs Energy

• If we calculate gibbs energy change from the cycle pattern according to hess's law and then by the relation G = H -TS, will it give the same value ??

• Originally posted by hoay:

If we calculate gibbs energy change from the cycle pattern according to hess's law and then by the relation G = H -TS, will it give the same value ??

If you intend to apply Hess' Law to Gibbs free energy cycle, note that all steps in the cycle must all be in terms of Gibbs free energy (and not some steps inolving enthalpy, some entropy and some Gibbs free energy).

Provided it's for the *same* reaction under the exact *same* conditions (ie. temperature, pressure, solvent, etc), then you should get the same value, whether you calculate the Gibbs free energy change for a particular reaction by applying Hess' Law (and given Gibbs free energy change values for several *different* but related equations in a cycle), or by applying delta G = delta H - T x delta S (and given the enthalpy change and entropy change values for the exact *same* reaction as what you're calculating Gibbs free energy change for).

• thanks for helping