## Significance of Constant Pressure and Constant Volume

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

Baoying Li 1B
Posts: 113
Joined: Sat Aug 17, 2019 12:18 am

### Significance of Constant Pressure and Constant Volume

When calculating the change of entropy and enthalpy, when do we consider the situation of constant pressure and constant volume? What is the difference?

nicolely2F
Posts: 149
Joined: Sat Sep 14, 2019 12:17 am

### Re: Significance of Constant Pressure and Constant Volume

From what I've seen in the textbook, the questions will most likely clearly state whether we should consider constant volume / pressure / temperature / etc.
At constant pressure, use: ΔH = ΔU + P.ΔV
At constant volume, use: ΔH = Q(v) (that is, equal to the heat received by the system)