## Spontaneity

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

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

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

Max Hayama 4K
Posts: 63
Joined: Fri Sep 28, 2018 12:16 am

### Spontaneity

Why is it that if deltaS total is positive we can immediately assume the reaction is spontaneous? I understand that if just deltaS is positive, its difficult to determine whether or not the reaction will be spontaneous. But if deltaS total is positive we can immediately assume the reaction is spontaneous regardless of what the temperature and enthalpy are?

Nathan Mariano 2G
Posts: 68
Joined: Fri Sep 28, 2018 12:29 am

### Re: Spontaneity

In order for a spontaneous reaction to occur, delta G must be negative. For a spontaneous reaction to occur, delta H must be negative and delta S must be positive. For a nonspontaneous reaction to occur, delta H must be positive and delta S must be negative.

megan blatt 2B
Posts: 61
Joined: Fri Sep 28, 2018 12:28 am

### Re: Spontaneity

Delta S total is the sum of delta S of the system and delta S of the surroundings. According to the second law of thermodynamics, a spontaneous change is accompanied by an increase in the total entropy of the system and its surroundings. Therefore, if there is an increase in the entropy of the system and its surroundings (in other words, an increase in the total entropy) then we know the reaction must be spontaneous.

Tatum Keichline 2B
Posts: 64
Joined: Fri Sep 28, 2018 12:26 am

### Re: Spontaneity

deltaG must be negative for a spontaneous reaction, so T deltaS must be a positive term to make sure the number subtracted from deltaH in deltaG=deltaH-TdeltaS has deltaH as a large negative number.