## delta U [ENDORSED]

isochoric/isometric: $\Delta V = 0$
isothermal: $\Delta T = 0$
isobaric: $\Delta P = 0$

Hector Acosta Discussion 1H
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### delta U

If there is no change in temperature is $\Delta U$ 0?

Mitch Mologne 1A
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### Re: delta U

Not necessarily. There can be work done.

Posts: 57
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### Re: delta U

Yes, like Mitch said above, delta U has two components, as seen in the equation deltaU = q + w (the first law of thermodynamics). Even if change in temperature is 0, and q is 0, work can still be done and affect internal energy.

Chem_Mod
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### Re: delta U  [ENDORSED]

If there is no change in temperature in an ideal gas then Delta U is always zero.

However, that does not mean q = 0 and w = 0.

As I discussed in class for the isothermal expansion of an ideal gas: q = -w (meaning they cancel each other resulting in Delta U = 0)

DianaTrujillo2K
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### Re: delta U

Can someone explain why delta U is 0 in the isothermal expansion of an ideal gas?

ClaireHW
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### Re: delta U

Can someone also explain under what conditions is delta U equal to zero?

(Claire Woolson Dis 1K)

Sophie 1I
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### Re: delta U

I know that delta U is 0 for isothermal reactions but I'm not sure why that is

Toru Fiberesima 1L
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### Re: delta U

Recall that dU=q+w. For an isothermal expansion q=-w. Also, temperature does not change (hence isothermal), therefore q=0. If q=0 then w=0. Thus, dU=0+0=0.

Joanna Pham - 2D
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### Re: delta U

In lecture yesterday for one of the review problems that asked to calculate deltaS of an isothermal reaction, Lavelle mentioned that U = (3/2)nRT. Thus, If there’s no change in temperature, since n, R, and T are all constant, that means there’s no change in internal energy.

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### Re: delta U

With isothermal reversible expansion, work of expansion is being done by the system so energy is being lost. However, a heat reservoir also adds heat back into the system, so temperature remains constant. This is why q=-w.

JT Wechsler 2B
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### Re: delta U

deltaU can equal 0 when there is no temperature change or q is equal to -w.