- #1

twmggc

- 5

- 0

## Homework Statement

Air is expanded in a piston-cylinder arrangement at a constant P of 200kPa from a volume of 0.1 m

^{3}to a volume of 0.3m

^{3}. Then the temperature is held constant during an expansion to a volume of 0.5m

^{3}. Predict the total work done in the air.

## Homework Equations

W = ∫PdV , PV = nRT

## The Attempt at a Solution

For the first part of the expansion I used:

W = ∫PdV = P∫dV = P(V

_{2}- V

_{1}) = 200,000Pa ( 0.3-0.1)m

^{3}

and got W = 40,000J.

The next expansion is what is confusing me.

Since Pressure is no longer constant I need to leave it in the W = ∫PdV equation.

So, I transform this equation using the ideal gas eqn. PV = nRT and get:

W = nRT∫dV/V = nRT*ln(V3/V2)

But, without knowing the n or the T how do I get the work?

Thanks!