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Postby 804994652 » Sun Feb 10, 2019 11:15 am

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???

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Joined: Fri Sep 28, 2018 12:15 am

Re: 4C.3

Postby aisteles1G » Sun Feb 10, 2019 11:33 am

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!

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