## Equations for w

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

Jessica Tsui 1H
Posts: 30
Joined: Fri Sep 28, 2018 12:21 am

### Equations for w

I'm a little confused. What was the point of showing the integral for the work equation to arrive at the same work of expansion equation (w = -P$\Delta$V)?

Kyle Golden Dis 2G
Posts: 67
Joined: Fri Sep 28, 2018 12:17 am

### Re: Equations for w

Dr. Lavelle was basically showing us the proof behind the work equation which is why he got the integral.

Brian Chhoy 4I
Posts: 66
Joined: Fri Sep 28, 2018 12:16 am

### Re: Equations for w

The integral equation is used when calculating reversible expansion done by a gas, since in this case it is set up so that the change in pressure occurs in small increments till it reaches the volume it should be at in equilibrium. In reversible expansion, the external and internal pressures are nearly identical so that the small changes in pressure will cause a change in the volume. The integral is later substituted for a ln(V2/V1) in the function.

Annalyn Diaz 1J
Posts: 61
Joined: Fri Sep 28, 2018 12:15 am

### Re: Equations for w

Brian Chhoy 4I wrote:The integral equation is used when calculating reversible expansion done by a gas, since in this case it is set up so that the change in pressure occurs in small increments till it reaches the volume it should be at in equilibrium. In reversible expansion, the external and internal pressures are nearly identical so that the small changes in pressure will cause a change in the volume. The integral is later substituted for a ln(V2/V1) in the function.

Why is the integral replaced with the ln(V2/V1)?

SydBenedict2H
Posts: 60
Joined: Wed Nov 08, 2017 3:00 am

### Re: Equations for w

So does this mean we aren't going to have to use the integral formula to calculate anything on tests?

MichaelMoreno2G
Posts: 60
Joined: Fri Sep 28, 2018 12:26 am

### Re: Equations for w

SydBenedict2H wrote:So does this mean we aren't going to have to use the integral formula to calculate anything on tests?

Most likely not, but I would still know it just in case.

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