## Why is delta U = 0 for isothermal reactions?

Tiffany Chao 2H
Posts: 117
Joined: Fri Aug 09, 2019 12:17 am

### Why is delta U = 0 for isothermal reactions?

In my notes, it says that it's because delta U = 3/2(nR*delta T) and if delta T = 0, then delta U will be 0. I can understand that logic but where did that delta U = 3/2(nR*delta T) equation come from? And why is it 0?

Thanks

christabellej 1F
Posts: 109
Joined: Sat Aug 17, 2019 12:17 am

### Re: Why is delta U = 0 for isothermal reactions?

U would equal 0 because it is an isothermal reversible equation, as the internal energy of the system does not change overall.

Christineg1G
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### Re: Why is delta U = 0 for isothermal reactions?

For an isothermal reaction, the temperature is constant so the internal energy would also be constant (delta U=0).

Jessica Li 4F
Posts: 115
Joined: Fri Aug 09, 2019 12:16 am

### Re: Why is delta U = 0 for isothermal reactions?

Delta U is 0 for an isothermal reaction because it is a state function and overall everything cancels out. This means that q + w = 0.

Eva Zhao 4I
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Joined: Sun Sep 29, 2019 12:16 am

### Re: Why is delta U = 0 for isothermal reactions?

To add on, I believe the 3/2 in your equation came from 'Ideal gas, Cv = (3/2) R' (which can be found on the formula sheet). Note that this 'C' value varies depending on what you're trying to solve for, i.e. 'Ideal gas, Cp = (5/2) R'.

Joanne Lee 1J
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Joined: Thu Jul 25, 2019 12:15 am

### Re: Why is delta U = 0 for isothermal reactions?

Delta U is zero for isothermal reactions because the internal energy of the system does not change.

Kyle Rex 1K
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Joined: Sat Aug 17, 2019 12:16 am

### Re: Why is delta U = 0 for isothermal reactions?

since its isothermal it means energy cannot come in or leave, so by nature the change in energy would be zero

Harry Zhang 1B
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Joined: Sat Sep 14, 2019 12:16 am

### Re: Why is delta U = 0 for isothermal reactions?

In an isothermal process, the average kinetic energy of the molecules stay the same and since there is no force between the molecules, the potential energy also stays the same. Therefore, delta U=0.

Astrid Lunde 1I
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### Re: Why is delta U = 0 for isothermal reactions?

U is equal to 0 because it is an isolated system so there is no energy energy leaving or going into the system.

Zoe Gleason 4F
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Joined: Tue Jul 23, 2019 12:15 am

### Re: Why is delta U = 0 for isothermal reactions?

The temperature is constant, and no energy will enter or leave the system. Therefore, ΔU=0.

Ying Yan 1F
Posts: 101
Joined: Fri Aug 02, 2019 12:16 am

### Re: Why is delta U = 0 for isothermal reactions?

An isothermal system is one where no heat nor matter is transferred externally, meaning that the energy will always stay the same in the system. That is why U=0 in an isothermal reactions.

Anish Natarajan 4G
Posts: 51
Joined: Thu Jul 25, 2019 12:16 am

### Re: Why is delta U = 0 for isothermal reactions?

Delta U is the change in internal energy of a system, which is dependent on its temperature. If T=0 then Delta U=0

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