## 4C.3

804994652
Posts: 68
Joined: Fri Sep 28, 2018 12:26 am

### 4C.3

In the 7th Ed. section 4c. #3 it asks that you find the final T and change in enthalphy when a) @ constant pressure and b) @ constant volume
I know when there is constant pressure the change in enthalpy, delta H= q
Is it the same for when there is constant volume?
delta H=q???

aisteles1G
Posts: 117
Joined: Fri Sep 28, 2018 12:15 am

### Re: 4C.3

At constant volume you have to use the delta H= deltaU (internal Energy) + work equation. The thing you have to know though is that deltaU=q when there is constant volume so you can use the q from part a as your delta U in part b. To find enthalpy you still need work though and the equation to use is w=-nR delta T, so you need to find Tf before you can find work and enthalpy. To find Tf use q=mCdeltaT, you have your heat q (765) and then moles (.82) and for C use Cv= 3/2(R) and delta T as Tf-298, so the equation should look like 765=.82*8.3*3/2*(tf-298). Solve for Tf to find delta T and plug that into deltaH=765+(-.82)*8.3*deltaT.
At constant Pressure: H=q
At constant Volume: U=q
Hope this helps!

Return to “Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)”

### Who is online

Users browsing this forum: No registered users and 1 guest