## calculation of work of irreversible and reversible expansion

$w=-P\Delta V$
and
$w=-\int_{V_{1}}^{V_{2}}PdV=-nRTln\frac{V_{2}}{V_{1}}$

Lorena Zhang 4E
Posts: 63
Joined: Fri Sep 28, 2018 12:16 am

### calculation of work of irreversible and reversible expansion

In order to calculate work, do we use internal or external pressure? For example, in the case of irreversible expansion, when the external pressure is smaller than the internal one, do we use the external or the internal? Do we always use the external/internal pressure when calculating the work?

Chem_Mod
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### Re: calculation of work of irreversible and reversible expansion

Use the pressure that is being pushed against.

If the system is expanding (say 2 atm initial pressure for the system) and pushing against a constant external pressure of 1 atm then use 1 atm.

If the expansion or compression is reversible (equilibrium pathway) then use either external or internal pressure as they are the same.

IsabelLight2H
Posts: 34
Joined: Wed Oct 03, 2018 12:15 am

### Re: calculation of work of irreversible and reversible expansion

Can someone explain the differences between reversible and irreversible reactions?

IsabelLight2H
Posts: 34
Joined: Wed Oct 03, 2018 12:15 am

### Re: calculation of work of irreversible and reversible expansion

How do I know if an expansion is reversible and irreversible?

IsabelLight2H
Posts: 34
Joined: Wed Oct 03, 2018 12:15 am

### Re: calculation of work of irreversible and reversible expansion

How do I know if an expansion is reversible and irreversible?

IsabelLight2H
Posts: 34
Joined: Wed Oct 03, 2018 12:15 am

### Re: calculation of work of irreversible and reversible expansion

What formulas do we use for reversible vs irreversible and why do we not use the same equation?