## Hess's Law

$w=-P\Delta V$
and
$w=-\int_{V_{1}}^{V_{2}}PdV=-nRTln\frac{V_{2}}{V_{1}}$

Dakota_Campbell_1C
Posts: 51
Joined: Fri Sep 28, 2018 12:15 am

### Hess's Law

When calculating the overall enthalpy, particularly with the bond enthalpy problems will the bond energies always be given to us and if not how do we calculate them?

Janice Park 1E
Posts: 36
Joined: Fri Sep 28, 2018 12:22 am

### Re: Hess's Law

Yes! The bond enthalpies will typically be given to us when solving for reaction enthalpy using bond enthalpies - I would be quite surprised if they were not. You just have to make sure you correctly add the bond enthalpies of all bonds broken and all bonds formed, respectively.
Also, Hess's Law is used in Hess's Method for solving for reaction enthalpies, not with bond enthalpies. We typically correlate it with the summation of different reaction equations.

Ray Huang 1G
Posts: 30
Joined: Fri Sep 28, 2018 12:20 am

### Re: Hess's Law

The bond enthalpies should be given or else we can't really solve the problem.