## Delta G [ENDORSED]

$\Delta G^{\circ}= \Delta H^{\circ} - T \Delta S^{\circ}$

$\Delta G^{\circ}= -RT\ln K$

$\Delta G^{\circ}= \sum \Delta G_{f}^{\circ}(products) - \sum \Delta G_{f}^{\circ}(reactants)$

Emma Ward 2C
Posts: 32
Joined: Fri Sep 29, 2017 7:05 am

### Delta G

why is delta G always negative?

miznaakbar
Posts: 55
Joined: Thu Jul 13, 2017 3:00 am
Been upvoted: 4 times

### Re: Delta G

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
Posts: 73
Joined: Fri Sep 29, 2017 7:07 am

### Re: Delta G

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.

Posts: 60
Joined: Sat Jul 22, 2017 3:00 am
Been upvoted: 1 time

### Re: Delta G

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
Posts: 53
Joined: Fri Sep 29, 2017 7:04 am

### Re: Delta G  [ENDORSED]

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