Pressure/Temp/Volume question

[itr]

Homework Statement

One mole of an ideal gas at 300K expands isothermally from a pressure of 2x10^6 N/m^2 to a pressure of 2x10^5 N/m^2.

Derive the equations for, and calculate:

the heat absorbed by the gas...
the change in the internal energy of the gas...
the entropy change in the gas if it expands reversibly

Homework Equations

Q=mc(Δt)
ΔE = Q - W
PV = nRT
W = PΔV
Another equation involving ΔE, but i am not sure what it is...

The Attempt at a Solution

Since it is an isothermic equation, there is no Δt...which makes the ΔE equal zero(the internal energy). Since the internal energy is zero, that makes the equation ΔE=Q-W into Q=W. I am not sure how to finish the problem, because i have a change in pressure...but there is no change in temperature...

 

[ideasrule]

Work is just the area under a PV diagram. Draw out the diagram, label V1 and V2 (the initial and final volumes), and you'll see what the area is.

 

[itr]

how do i know what the change in volumes are? all i know is there is a pressure decrease, which could mean anything...unless i am missing something