luv's G-Chem Question #3

[luv8724]

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Which of the following gas properties is needed to calculate the work
done by an expanding gas?

I. The initial and final pressures
II. The initial and final volumes
III. The path followed during the expansions

A. I only
B. II only
C. I and II only
D. I, II, and III

 

[UCB05]

work is not a state function. The path taken will determine the total work done, therefore III has to be in the answer.

 

[Erhatstil]

work is not a state function. The path taken will determine the total work done, therefore III has to be in the answer.

so the answer must be D right? because the changes in volume allow us to solve the work equation. eventhough work is not a state function, we still need those variables to solve for it

 

[predent7]

it is a good problem..

W=(integration)PdV
or
work = pressure [Vf(g)-Vi(l)], or
work equals pressure * (finial volume - initial volume)


State functions are : P,V,T,G,H,S,Density
Path fn. are : W,Q

 

[luv8724]

okay... so we put P as in a positive P right? since we assume that P is constant and really only difference we will have to find is the final volume - initial volume to do work

 

[UCB05]

You can't just assume P is constant the whole time. If this is stipulated, then yes, you can calculate work that way. If it is not, as in this case, you need to know P1, P2, V1, V2, and the path taken during the expansion.

A gas that expands from 1L to 2 L due to low-pressure conditions does less work on surroundings than a gas that expands against a large amount of pressure (as in if it were heated).

 

[predent7]

When I say :

W=(integration)PdV
or
work = pressure [Vf(g)-Vi(l)]

P is a function of V, so we need to know initial and final P and V.. so you are right !