Work and internal energy for monatomic ideal gas on PV diagram

[prj]

Homework Statement

Suppose a monatomic ideal gas is changed from state A to state D by one of the processes shown on the PV diagram (attached). a) Find the total work done on the gas if it follows the constant volume path A-B followed by the constant pressure path B-C-D. b)Calculate the total change in internal energy of the gas during the entire process and the total heat flow into the gas.

Homework Equations

W= -P(Vf-Vi)
dU = Q + W
dU = 3/2nRT

The Attempt at a Solution

I found the answer to part A to be 1215.6 J of work were done on the gas. My problem comes in part b. How can I determine the change in internal energy without knowing the number of moles (n) of the gas, or the temperature?

 

[cosmic dust]

Do you really need n to calculate the change in internal energy? Remember that U depends only on temperature, so what is the temperaure difference?

 

[TSny]

dU = 3/2nRT

How can I determine the change in internal energy without knowing the number of moles (n) of the gas, or the temperature?

Shouldn't that be dU = 3/2nRdT? Or ΔU = Δ(3/2nRT)? Maybe you can use the ideal gas law to write this in terms of P and V rather than nRT.

 

[prj]

I think I was over-complicating the problem, but I've solved it now.

Thank you for the help!