# Change in Entropy of an expanding gas

**1. The problem statement, all variables and given/known data**

Four moles of an ideal gas expands at constant temperature until its pressure is reduced to half of its initial value. What is the change in entropy of the gas?

**2. Relevant equations**

ΔS=Q/T (For constant T) pinitial=p pfinal=.5p

Q=W

W=pdv

nrTln(vf/vi)

**3. The attempt at a solution**

I tried using nrTln(vf-vi), but realized I cant do that not knowing the temperature or the volumes. Is there an equation using deltap that I could use to solve for this that I am unaware of or can’t figure out? Thanks

http://ift.tt/1eZGIju

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