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### Spontaneity

Posted: Tue Feb 19, 2019 10:11 pm
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?

### Re: Spontaneity

Posted: Tue Feb 19, 2019 10:19 pm
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.

### Re: Spontaneity

Posted: Tue Feb 19, 2019 10:25 pm
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.

### Re: Spontaneity

Posted: Tue Feb 19, 2019 10:40 pm
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.