## Signs for entropy

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

AlyssaBei_1F
Posts: 99
Joined: Fri Sep 28, 2018 12:17 am

### Signs for entropy

When do you use -delta H/T versus +delta H/T?

ChathuriGunasekera1D
Posts: 78
Joined: Fri Sep 28, 2018 12:17 am

### Re: Signs for entropy

Hi! You use the sign based on whatever your given ΔH is. If you aren't sure about that, you can use q and see if the temperature increased or decreased to see if the reaction is endothermic or exothermic. Endothermic reactions absorb heat, and the temperature increases so q is positive and ΔH is positive.

PranitKumaran1F
Posts: 30
Joined: Thu Nov 08, 2018 12:17 am

### Re: Signs for entropy

If the reaction is endothermic, you know that delta H is positive because the reaction absorbs heat. If the reaction is exothermic, then delta H would be negative because the reaction gives off heat.

LorenzoDuvergne3I
Posts: 60
Joined: Fri Sep 28, 2018 12:25 am

### Re: Signs for entropy

Is H/T used for every state other than constant pressure? I'm confused about when to use one over the other.

Charles Gu 1D
Posts: 60
Joined: Fri Sep 28, 2018 12:16 am

### Re: Signs for entropy

A positive delta H is for endothermic reactions which will absorb heat and also increase entropy. A negative Delta h is for exothermic reactions which will entropy to decrease since heat is released

harshitasarambale4I
Posts: 58
Joined: Fri Sep 28, 2018 12:26 am

### Re: Signs for entropy

How would you determine the signs for enthalpy?