Irreversible Vs. Reversible Expansion

[Carolina Gomez 2G]

When solving for work of expansion, what is the difference between an irreversible expansion and an isothermal reversible expansion?
What are the equations for work we should use to solve for reversible and irreversible expansion?

[Brittney Nguyen 2L]

Hi!

An irreversible expansion occurs when the pressure of the surroundings is constant and not equal to the pressure of the system. The system will expand rapidly if given the opportunity to. We should use the equation w = -P*deltaV for irreversible expansion.

An isothermal reversible expansion occurs when the pressure of the surroundings and system are pretty much equivalent. The pressure of the surroundings is decreased in infinitesimally small amounts so that the expansion of the system occurs in infinitesimally small intervals. Because the work of expansion is being done slowly, heat energy will replace the energy of work being done by the system, keeping the internal energy and temperature of the system the same. We should use the equation w = -nRt*ln(V2/V1) for reversible expansion.

I hope this helps!

[Asia Yamada 2B]

When there is an irreversible expansion, you use the formula: w = -P•deltaV where P is the external pressure which is constant. When there is an isothermal reversible expansion, you use the formula: w = -nRT•ln(V2/V1).

[EmilyC_3D]

Everyone else gave really good explanations on how to differentiate these two types of expansions! Dr. Lavelle also has charts under the outlines for Thermodynamics that show diagrams of the difference between the two expansions that really helped me while I was studying.

[Kathy_Li_1H]

Hi! Reversible expansions utilize the equation w=-nRTln(V2/V1), have a delta S total equal to zero, and are usually have a greater work value than the irreversible counterpart. Irreversible expansions utilize the w=-P(delta V), involve less work done, and have a delta S surroundings equal to 0.