## Delta U equals zero

$\Delta U=q+w$

Matt Sanruk 2H
Posts: 131
Joined: Wed Sep 18, 2019 12:21 am

### Delta U equals zero

What would be an example of delta U equaling to zero?

Posts: 74
Joined: Fri Sep 28, 2018 12:29 am

### Re: Delta U equals zero

An isothermal expansion

One of the characteristics of an ideal gas is that there is no interaction between gas molecules. This means the molecules will not have any potential energy so the only contributor to the change in internal energy would be its kinetic energy due to its absolute temperature. Since it is isothermal, T=0 so neither kinetic nor potential energy would contribute to the change in internal energy so deltaU=0.

Matt Sanruk 2H
Posts: 131
Joined: Wed Sep 18, 2019 12:21 am

### Re: Delta U equals zero

So this is for constant pressure and ideal gas?

Zaynab Hashm 2I
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Joined: Wed Sep 11, 2019 12:15 am
Been upvoted: 1 time

### Re: Delta U equals zero

it would be for an isothermal reaction when the temperature is constant

Matt Sanruk 2H
Posts: 131
Joined: Wed Sep 18, 2019 12:21 am

### Re: Delta U equals zero

Sorry yes I meant temperature, thanks!

Anthony Hatashita 4H
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Joined: Wed Sep 18, 2019 12:21 am

### Re: Delta U equals zero

Considering the first law equation, work and heat would have to equal 0. For an isothermal process, heat is 0, so if there is a reaction that is isothermal that does no work, delta U should be 0.

205291012
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Joined: Mon Nov 11, 2019 12:17 am

### Re: Delta U equals zero

delta U would be 0 if it is isothermal and no work is done. imagine a gas expanding in a vacuum with constant temperature. since it is not pushing against anything, no work is done and there is no change in temperature so delta U is 0.

Sean Cheah 1E
Posts: 105
Joined: Wed Sep 18, 2019 12:20 am

### Re: Delta U equals zero

As noted previously, all isothermal processes by definition have delta U = 0. This means that the work done does not necessarily have to be 0. In the case that work is not zero, q will simply be the negative of that so they cancel out.