## Second Law application

$\Delta S = \frac{q_{rev}}{T}$

Ardo 2K
Posts: 31
Joined: Fri Sep 29, 2017 7:05 am

### Second Law application

According to the second law of thermodynamics the natural progression of a system along with its surroundings is from lower entropy to higher entropy, so wouldn't that mean that a reaction with a positive change in entropy be a spontaneous one? But when we implement Gibbs free energy we see that under certain scenarios a negative entropy can constitute a spontaneous reaction as well. So is it more safe to look at the sign of the Gibbs free energy in order to decide if a reaction is spontaneous or not?

Virpal Gill 1B
Posts: 32
Joined: Thu Jul 27, 2017 3:00 am

### Re: Second Law application

When looking at entropy, the reaction is determined to be spontaneous if $\Delta S$total is greater than zero. $(\Delta Stotal= \Delta S system+\Delta Ssurroundings)$) So even if the entropy of the system decreases, the reaction can still be spontaneous if the entropy of the surroundings increases enough.

Justin Bui 2L
Posts: 51
Joined: Fri Sep 29, 2017 7:06 am

### Re: Second Law application

I also was wondering the same thing, where delta G would still be negative (spontaneous) even if delta S were negative, as long as the reaction was exothermic enough (delta H is a large negative).

Tim Nguyen 2J
Posts: 31
Joined: Sat Jul 22, 2017 3:00 am

### Re: Second Law application

Gibbs Free Energy is heavily dominated by the enthalpy term. Even though entropy can be negative in terms of the system, the reaction overall can still be spontaneous as stated above by its relation to the entropy of surroundings.