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

Posted: Mon Feb 10, 2020 2:30 am
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

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

Posted: Mon Feb 10, 2020 8:06 am
U would equal 0 because it is an isothermal reversible equation, as the internal energy of the system does not change overall.

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

Posted: Mon Feb 10, 2020 8:46 am
For an isothermal reaction, the temperature is constant so the internal energy would also be constant (delta U=0).

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

Posted: Mon Feb 10, 2020 11:42 am
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.

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

Posted: Mon Feb 10, 2020 1:09 pm
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'.

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

Posted: Mon Feb 10, 2020 5:33 pm
Delta U is zero for isothermal reactions because the internal energy of the system does not change.

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

Posted: Thu Feb 13, 2020 10:53 pm
since its isothermal it means energy cannot come in or leave, so by nature the change in energy would be zero

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

Posted: Thu Feb 13, 2020 11:14 pm
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.

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

Posted: Fri Feb 14, 2020 10:13 am
U is equal to 0 because it is an isolated system so there is no energy energy leaving or going into the system.

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

Posted: Fri Feb 14, 2020 10:14 am
The temperature is constant, and no energy will enter or leave the system. Therefore, ΔU=0.

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

Posted: Sun Feb 16, 2020 12:53 pm
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.

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

Posted: Sun Mar 01, 2020 9:41 pm
Delta U is the change in internal energy of a system, which is dependent on its temperature. If T=0 then Delta U=0