# Thermochem, thermodynamics, diatomic gas at constant volume

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1. Feb 24, 2016

### Diamond101

1. The problem statement, all variables and given/known data
A sample consisting of one mole of a diatomic perfect gas is heated from 25 °C to 200 °C at constant volume. Calculate q, w, ΔU and ΔH for the process, given that Cv = 23.02 J K-1 mol-1 .

2. Relevant equations
Im studying for mid terms and i have no lecture notes on diatomic gas looking online currently haven't found much. Please explain

3. The attempt at a solution
du=w-cvdt
cv=5/2nr

2. Feb 24, 2016

### Staff: Mentor

You don't need to know what a diatomic gas is to solve this problem. They give you the value of the heat capacity. That's all you need.

If the volume of gas is constant, how much work is done?

What is that Cv doing that equation that you wrote? The equation is incorrect. It should read ΔU=Q-W

3. Feb 24, 2016

### Diamond101

wont it be du=q+w
w=-pdv
du=q-pdv
du=qv at const volume .

4. Feb 24, 2016

### Diamond101

how do i find work , work it -pdv right? i wasnt given pressure or is it understood as 1 bar and i wasnt given a volume

5. Feb 24, 2016

### Staff: Mentor

If the volume doesn't change, what is dv equal to?

6. Feb 24, 2016

### Diamond101

0, and because w=pdv no work is done ? is this an isochoric process? would du=n cvdt

7. Feb 24, 2016

### Staff: Mentor

Very nice. Yes. isochoric is synonymous with constant volume. And your equation for the differential change in internal energy is correct.

Chet

8. Feb 24, 2016

### Diamond101

i figured it out i got 4.028 kj
w=0
du=q+w
du=Q
q+du are the same
dh=du +pdv
q=ncvdt

9. Feb 24, 2016

### Diamond101

thank you ever so much