Expansion vs Compression

[Alan Limones 1H]

Hi, when we are dealing with expansion and compression (not in the same problem, but separately), how would we apply the work equation to that problem to each scenario of expansion or compression? Or are there different equations we use for each scenario?

[Max Kaminsky [3L]]

Since work is -P∆V or -nRTlnV₂/V₁ (depending on if the expansion/compression is reversible or not), the difference between expansion and compression is in the V. ∆V and lnV₂/V₁ are positive for expansion and negative for compression. There is no need to use an entirely different equation.

[Drake Snyder 1F]

Expansion means that the system is doing work on the surroundings, and compression means that the surroundings are doing work on the system. If the temperature is held constant (isothermal) the work equation for irreversible expansion will be w = -PdeltaV, and for reversible expansion, w = -nRTln(V2/V1). You should use the same equation for irreversible compression that you did for expansion. Hope this helps!