Change in the internal energy of an isobaric process

[Stendhal]

Homework Statement

A cylinder contains 0.250mol of carbon dioxide (CO2) gas at a temperature of 27.0∘C. The cylinder is provided with a frictionless piston, which maintains a constant pressure of 1.00atm on the gas. The gas is heated until its temperature increases to 127.0∘C. Assume that the CO2 may be treated as an ideal gas.

Homework Equations

ΔU = ΔQ -W

ΔU = C_v*n*ΔT

The Attempt at a Solution

In this case, I thought that ΔU could be set equal to (5/2)nRΔT since we know all of those variables. The value I got for that was ΔU = 520J, but that isn't the correct answer. Any help in explaining where I am going wrong would be appreciated greatly!

 

[Chestermiller]

Did you look up the value of Cv on line or in the literature?

 

[Stendhal]

Whoops, to answer that, I did. The value I looked up however was not in units of moles, so I got the wrong answer. Found a value of Cv in moles and got the right answer.