[yammer]

I have a problem on a chem final review question

A gas releases 65.4 j into the surroundings and is compressed by 0.335L against a Presure of 0.965 atm. Find Delta E

I was thinking to use

DE= q-pDv

   = -65.4-0.965(-0.335)
   = -64.876
This is not one of the choices in the multiple choice?

The given answer is -32.4 J?

Half of my answer, what did I do wrong?

[Demotivator]

The units are inconsistent. Joules vs liter-atm.

[Donaldson Tan]

this sounds like a standard thermodynamics equation.

assuming this is a close system,

dU = Q + W
Q = -65.4J (heat given out to surroundings)
W = p.dV

although you are right to use p.dV = 0.965(0.335), the answer you get is not in Joules. In order to get joules, you must convert p to Pascal and dV to m³

[GCT]

I have a problem on a chem final review question

A gas releases 65.4 j into the surroundings and is compressed by 0.335L against a Presure of 0.965 atm. Find Delta E

I was thinking to use

DE= q-pDv

   = -65.4-0.965(-0.335)
   = -64.876
This is not one of the choices in the multiple choice?

The given answer is -32.4 J?

Half of my answer, what did I do wrong?

it's an open system,

I think that one of the key factors here is that the work is not simply PdeltaV. This applies when a gas expands against a constant pressure atmosphere.  However, you're compressing the gas, meaning that the pressure will be different at each point of the compression.

[GCT]

Another possibility is that part of the heat lost to the surroudings, is actually used to do work upon the gas.  Just trying to offer some suggestions here.

[Donaldson Tan]

dU = Q + W
Q = -65.4J (heat given out to surroundings)
W = p.dV

i made a mistake. W = - p.dV (i omitted the minus sign previously)