Work done on/by hydrogen gas

1. Dec 4, 2008

Shayna

1. The problem statement, all variables and given/known data
The figure shows a thermodynamic process followed by 1.80×10−2 mol of hydrogen.

How much work is done on the gas?
By how much does the thermal energy of the gas change?
How much heat energy is transferred to the gas?

The attempt at a solution
I thought the work done to gas should be negative the area underneath the curve, which is
W= [(300-100)*0.001L * (4-1)atm] = (3 atm * 0.2L)/2 = 0.3 L*atm = 0.3*101.3 J = 30.39 J
apparently that is neither here nor there

Also, the thermal energy of the gas change would be the same as the amount of work done on the gas plus heat energy transferred to the gas, is that correct?

Pleeeeeease hep, I am so confused.

2. Dec 4, 2008

tiny-tim

Hi Shayna!

Hint: work done = force times change in position = pressure times change in volume.

3. Dec 5, 2008

Shayna

Re: thermodynamic

enn, well, I calculated the area wrong, but how do I find out about the heat transfered?

4. Dec 5, 2008

tiny-tim

Hi Shayna!
(I think thermal energy and heat energy are the same … wikipedia certainly seems to think so: http://en.wikipedia.org/wiki/Heat_energy)

Yes, from the work-energy theorem, work done = energy transferred.

(that's the only reason anyone is interested in calculating work )

5. Dec 5, 2008

Shayna

Re: thermodynamic

I got the work done by calculating area under the curve which is -50.7J
I also calculated the temperature change delta T= T1-T2 = nR/(p1V1-p2V2)= -67.75K
I also tried specific heat, which q= Cq * n* delta T = 28.82 J/mol*K * 1.8*10^-2 mol * 67.2585 K = -35.1 J
I don't know where to go from here
Thanks so much for your help

6. Mar 23, 2010

Fromaginator

Re: thermodynamic

I'm stuck on this one myself but one thing I know is that the specific heat is the piece of knowledge missing here since the values for the specific heat one can look up are either c_p(for constant pressure) or c_v (for constant volume) and this problem has neither constant volume nor pressure.

7. Mar 24, 2010

Fromaginator

Re: thermodynamic

In just talked to someone about this apparently you use C_v to find the change in thermal energy. So it is just a matter of finding the two temperatures T=PV/nR then the change in temperature T_1-T_2. Then applying (delta)E_th=n*C_v*(delta)T