## Equations for work

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

MackenziePerillo-1L
Posts: 31
Joined: Fri Sep 28, 2018 12:19 am

### Equations for work

I am still confused as to when each equation for work is supposed to be used.
w=-p* Δv
w= - v1∫v2 Pdv
w=-nRT ln (v2/v1)

Can anyone specify in which type of case each equation is used?

megansardina2G
Posts: 61
Joined: Fri Sep 28, 2018 12:23 am
Been upvoted: 2 times

### Re: Equations for work

The first two are the same equation. They are used under constant pressure. (for the second: pressure is constant, so it can be taken outside the integral. The integral of dV is V, and V2-V1 is ∆V, thus the first equation: w=-p∆V)
The third equation is used when the reaction is isothermal, but pressure and volume are changing.

Simran Rai 4E
Posts: 58
Joined: Fri Sep 28, 2018 12:17 am

### Re: Equations for work

Adding to that, for the third equation, when pressure is changing, you'd use w=-nRT ln (p1/p2).

Michael Novelo 4G
Posts: 64
Joined: Fri Sep 28, 2018 12:28 am

### Re: Equations for work

also -PdeltaV refers to the irreversible function and -nRTln(v2/v1) refers to the reversible function. The reversible will always do more work since pressure is changing in infinite small amounts.

Erin Kim 2G
Posts: 75
Joined: Fri Sep 28, 2018 12:26 am

### Re: Equations for work

The first and second equations are the same; the second one simplified equals the first equation. These equations are used for situations in which the pressure is constant. However in irreversible functions in which the pressure is not constant, you would use the third equation. They all solve for work done by the system.

MackenziePerillo-1L
Posts: 31
Joined: Fri Sep 28, 2018 12:19 am

### Re: Equations for work

Thank you that was really helpful and clarified so much.

CristinaMorales1F
Posts: 31
Joined: Fri Feb 16, 2018 3:01 am

### Re: Equations for work

In what ways can the internal energy be changed in a closed system?

Heidi Ibarra Castillo 1D
Posts: 60
Joined: Fri Sep 28, 2018 12:19 am

### Re: Equations for work

the first two are definitely the same equation