Gibbs free energy

[andrea guzman 1F]

Under what conditions would delta H be zero and the reaction would be spontaneous?

[marina niland 3b]

For values of entropy that are large and positive.
Spontaneous reactions are when G is less than 0 (negative).
Because of the equation deltaG = deltaH - T*deltaS,
So deltaS must be large and positive, so it gets subtracted from deltaH which is ~0, making deltaG negative.

For deltaS to be large and positive, you must be going from a low to high entropy state.

[106046096]

Hi! delta H can be zero and the reaction would be spontaneous if delta S is positive and temp is positive.

[705984992]

One example to show this is the vaporization of liquid water at 100C. The enthalpy at this phase transition is 0. The entropy is positive because there's increased disorder from liquid to gas phase. As a result this example is still spontaneous.