Delta G [ENDORSED]

[Emma Ward 2C]

why is delta G always negative?

[miznaakbar]

Delta G isn't always negative because you calculate it using enthalpy and entropy (which are not always negative values). For instance, if delta H was a positive value and delta S was a small positive values, then delta G would be a positive value. Delta G being negative indicates that a reaction is spontaneous, so any non-spontaneous reactions would have a positive delta G.

[Tim Foster 2A]

Hey Emma,
Delta G is not always negative, it is a measure of the energy available to do work in a system. For example, because the hydrolysis of ATP allows your cells to harness the energy from that spontaneous reaction and do work with it, it has a negative Delta G. A reaction that requires an net input of energy to proceed has a positive Delta G, and is not considered a spontaneous reaction.

[RuchaDeshpande1L]

Delta G, or the Gibbs Free Energy, tells us if the reaction occurs spontaneously or not. Because it is a calculated value from enthalpy and entropy, it actually doesn't always have to be negative. We know that spontaneous reactions occur when delta G is negative through the derivation Dr. Lavelle did in lecture on Monday, 01/29. By using delta G(sys) = delta H(sys) - T * delta S(sys), we divide both sides by temperature and use the net equation for delta S(tot) to see that delta S(tot) = -delta G(sys)/T. Therefore, whenever delta G is negative, we can determine that the process is spontaneous due to the positive change in total entropy.

[104922499 1F]

Delta G is not always negative. When it is negative it implies that it is spontaneous. When it is positive it implies it is nonspontaneous