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blinder

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- Thread starter blinder
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- #1

blinder

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- #2

Q_Goest

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As you must already know PV^n = constant is a polytropic process. If you compress a gas, the work done is the integral of PdV. If we integrate that for a polytropic process you end up with:

W = (m R (T2 - T1) / (1-n) = (P2 V2 - P1 V1) / (1-n)

where m = mass

R = Gas Constant

T = temperature

n = polytropic exponent

P = absolute pressure

V = total volume

(for any value of n except 1)

For an isentropic compression, n = the ratio of specific heats of the gas (ex: 1.667 for a monotomic gas, 1.4 for a diatomic gas, etc...)

For an isobaric process, n = 0

For an isothermal process, n = 1 so you need to do the integration using n=1 which comes out to:

W = mRT ln (V2/V1) = mRT ln (P1/P2)

Hope that helps.

- #3

quark

- 231

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... or did you intend to ask this? http://webbook.nist.gov/chemistry/

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