## Phase changes and entropy

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

mendozayael_2H
Posts: 31
Joined: Fri Sep 29, 2017 7:06 am

### Phase changes and entropy

When we calculate phase changes, why is q in S = q/T replaced with the enthalpy H of the phase change? Is it just easier or a connection between q and H

Christiana2D
Posts: 23
Joined: Fri Sep 29, 2017 7:06 am

### Re: Phase changes and entropy

Since phase changes are typically given in delta H Fusion, etc. it's better to make that connection between delta H and q.

Michaela Capps 1l
Posts: 50
Joined: Thu Jul 27, 2017 3:00 am

### Re: Phase changes and entropy

Delta H is equal to q at a constant pressure.

Nate O 2L
Posts: 15
Joined: Fri Sep 29, 2017 7:06 am

### Re: Phase changes and entropy

Like Lavelle said, Enthalpy is just heat at constant pressure [q][/p].

Anika_Patel_1G
Posts: 32
Joined: Fri Sep 29, 2017 7:06 am

### Re: Phase changes and entropy

You can replace q with delta H when the system is at constant pressure. We often use the formula deltaS=deltaH/T when we are calculating the entropy change at boiling point or other phase changes. Just make sure when you do this, you use the correct T (the boiling point temperature).

Phillip Tran
Posts: 54
Joined: Thu Jul 13, 2017 3:00 am

dH=qp