Solving Flexible Balloon H2S Gas Problem: Q, ΔU, W & V

[gmarc]

Homework Statement

A flexible balloon contains 0.375 mol of hydrogen sulfide gas H2S. Initially the balloon of H2S has a volume of 6750 cm^3 and a temperature of 29.0 C. The H2S first expands isobarically until the volume doubles. Then it expands adiabatically until the temperature returns to its initial value. Assume that the H2S may be treated as an ideal gas with C_p = 34.60 J/mol*K and gamma = 4/3.

a) What is the total heat Q supplied to the H2S gas in the process?

b) What is the total change in the internal energy Delta U of the H2S gas?

c) What is the total work W done by the H2S gas?

d) What is the final volume V?

The Attempt at a Solution

For part A, I found Q = 3290J, which is the right answer.
For part B, I know that Delta U = nCv*Delta T, but I can't come out with the right answer. I'm sure once I find part B, the others will be much easier.

 

[kamerling]

they ask for the total change in the internal energy. For an ideal gas the internal energy only depends on the temperature.

 

[gmarc]

So if the change in temperature is 302K, that's the change in internal energy?

 

[kamerling]

So if the change in temperature is 302K, that's the change in internal energy?

In the second phase the temperature returns to its initial value.

 

[gmarc]

Ok, so the change in internal energy is equal to zero, and the total work done is just equal Q, the heat supplied. Now I just can't find the final volume in m^3

 

[kamerling]

you know that $$P V^{\frac {C_p}{C_v}} = constant$$ for adiabatic expansion?