Calculating Work

Haley Dveirin 1E · Postby **Haley Dveirin 1E** » Tue Jan 28, 2020 3:46 pm

Do you use a different equations to calculate work done in a reversible or irreversible expansion?

Ashley Tran 2I · Postby **Ashley Tran 2I** » Tue Jan 28, 2020 5:13 pm

Yes, there are two different equations
Irreversible: w=-P $\Delta$ V
Reversible (more work): w=-nRTln(V2/V1)

Sean Cheah 1E · Postby **Sean Cheah 1E** » Tue Jan 28, 2020 6:56 pm

More generally, $W =-\int_{V_{i}}^{V_{f}}P\ dV$ . In the case of an irreversible process against a constant pressure, this gives you $W = -P(V_{f} - V_{i}) = -P\Delta V$ . In the case of a reversible process, the P in the work equation is equal to the P of the gas -- the external pressure on the gas is always equal to the internal pressure of the gas. Thus, the ideal gas law can be used to yield $W =-\int_{V_{i}}^{V_{f}}\frac{nRT}{V}\ dV = -nRT[\ln(V_{f}) - \ln(V_{i})] = -nRT\ln\left (\frac{V_{f}}{V_{i}} \right )$

Eunice Nguyen 4I · Postby **Eunice Nguyen 4I** » Tue Jan 28, 2020 10:32 pm

Irreversible expansion (sudden isothermal expansion) is calculated: w=-Pex(deltaV)
Reversible expansion (gradual isothermal expansion) is calculated: w=-nRT * ln(vf/vi)

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Calculating Work

Calculating Work

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