Finding the change in pressure and entropy of a quasistatic adiabatic process

[rg2004]

Homework Statement

Suppose that one mole of an ideal gas expands in a quasi-static adiabatic process from P1 = 1 Pa and V1 = 1m3 to V2 = 8m3. What is the change in the pressure and the entropy of the gas?

Homework Equations

PV^\gamma=constant

The Attempt at a Solution

I can't come up with a second equation that doesn't introduce another unknown. I've been working on thermodynamics for the past two days almost non-stop and I'm drained. Any help would be nice. thanks.

 

[rg2004]

perhaps I am supposed to assume that the gas is monoatomic? My textbook is vague and its not clear to me whether all ideal gasses are considered monoatomic.

this is what i found:

\gamma= 5/3 (ideal monatomic gas).