Question

1) 0.19 litre of an ideal monatomic gas (Cv,m = 3R/2) initially at 83 °C and 47 atm pressure undergo an expansion against a constant external pressure of 1.19 atm, and do 2.3 kJ of work. The final pressure of the gas is 1.19 atm. Calculate the change in enthalpy, ΔH

2) Calculate the work, w, (in J) when 5.2 litre of an ideal gas at an initial pressure of 45.1 atm is expanded isothermally to a final pressure of 1.56 atm against a constant exteral pressure of 1.56 atm.
-I used the equation: w = -Pext(ΔV) and got -821.94 in J..it's wrong

Thank you!! :)

Answer 1

Try this for 2. It would have helped if you showed you work so we wouldn't need to guess what you did.
p1v1 = p2v2.
45.1*5.2 = 1.56*v2
I obtained approx 150 L for v2 but you should get a better answer.

Then work = -1.56(V2-V1) which gives an answer in L*atm. That x 101.325 will convert to J. My answer is approx -22 kJ.

Answer 2

1) dH = 3511.63 J

2) w = -22940.26 J