[legge]

1. The problem statement, all variables and given/known data

A chemical reaction is a gas mixture at 500 degrees C decreases the number of moles of gas, which is assumed to behave ideally, by 34.7%. If the internal energy change is 23.8 kJ, what is the value of dH.

2. Relevant equations

Not sure if they are complete relevant but...
d(PV) = d(nRT)
dH = dE + d(PV)

3. The attempt at a solution

So...what I was thinking of doing was using dH = dE + dPV.

We are given dE. To find d(PV), I was thinking of using d(nRT), because it tells us the change in moles. I feel that I'm close, but I know that you can't just put in the change in percent for the change in moles.

[Rabn]

You really are on the right track. Are you familiar with how to calculate changes in chemical potential? If so looking at those derivations would help you. When you expand the d(PV) term, you get PdV + VdP + dPdV, the final term is essentially zero. Does volume or pressure stay constant? Take a look at chemical potential and how to derive the different equations. The way I would approach the problem is to solve the equation as if there were no change in the number of moles, in which case you could ignore the n variable, then multiply that by the % change.

take a look at this website http://www.life.uiuc.edu/crofts/bioph354/thermo_eq.htm  particularly up to equation 3. That should help you figure out the equation. If you need more help get back to us.