# Adiabatic expansion of an ideal gas.

Problem: One mole of a diatomic ideal gas, initially having pressure P and volume V, expands so as to have pressure 2P and volume 4V. Determine the entropy change of the gas in the process.

Attempt: I thought this would just be R ln(V2/V1)... So, I said (8.314)*ln(4) but it's wrong...
There's an example almost exactly like it in my text book, and I don't see where I'm going wrong. The example they use just leaves the answer as 4R... Could I be using the wrong value for R?

I have a feeling that PV^gamma fits in there somehow, since we're given the fact that it's diatomic (gamma=1.4), but I don't know how... R ln(V2/V1) is an expression for the entropy change for an adiabatic process, right?