# Internal energy

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#1
So the internal energy is the sum of KE and PE and cannot be reduced to 0 even at absolute zero because the substance still has PE. But according to my textbook PE is 0 for gases and then gets more negative for liquids and solids.
So surely this would mean that at 0K a substance internal energy would be negative as 0(KE) + a large negative PE would be negative which doesn’t makes sense.

Is anyone able to Clear this up at all.
Also this is for a levels so please don’t go full on uni level explanation.

Thanks
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2 years ago
#2
(Original post by Snoozinghamster)
So the internal energy is the sum of KE and PE and cannot be reduced to 0 even at absolute zero because the substance still has PE. But according to my textbook PE is 0 for gases and then gets more negative for liquids and solids.
So surely this would mean that at 0K a substance internal energy would be negative as 0(KE) + a large negative PE would be negative which doesn’t makes sense.

Is anyone able to Clear this up at all.
Also this is for a levels so please don’t go full on uni level explanation.

Thanks

I am not why do you think that the internal energy has to reduce to zero at absolute zero kelvin.

At absolute zero a system of molecules (such as a quantity of a gas, a liquid, or a solid) has its minimum possible total energy (kinetic plus potential).

https://en.wikibooks.org/wiki/A-leve...#Absolute_zero

https://ipfs.io/ipfs/QmXoypizjW3WknF...lute_zero.html

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#3
(Original post by Eimmanuel)
I am not why do you think that the internal energy has to reduce to zero at absolute zero kelvin.

At absolute zero a system of molecules (such as a quantity of a gas, a liquid, or a solid) has its minimum possible total energy (kinetic plus potential).

https://en.wikibooks.org/wiki/A-leve...#Absolute_zero

https://ipfs.io/ipfs/QmXoypizjW3WknF...lute_zero.html

Thanks, I may not have explained my confusion very well. I know that it can’t be zero as there is the potential energy.

But what I don’t understand is that if the potential energy is negative surely that would mean that the internal energy would be less than 0 which makes no sense.
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2 years ago
#4
(Original post by Snoozinghamster)
Thanks, I may not have explained my confusion very well. I know that it can’t be zero as there is the potential energy.

But what I don’t understand is that if the potential energy is negative surely that would mean that the internal energy would be less than 0 which makes no sense.
Why it makes no sense for internal energy to be negative?
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#5
(Original post by Eimmanuel)
Why it makes no sense for internal energy to be negative?
Yeh,
0 KE + a negative PE gives a negative internal energy.
But also Internal energy can’t be zero, so can’t be less than zero.

Which doesn’t really make sense to me but that’s how I’m interpreting my textbook.
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2 years ago
#6
(Original post by Snoozinghamster)
Yeh,
0 KE + a negative PE gives a negative internal energy.
But also Internal energy can’t be zero, so can’t be less than zero.

Which doesn’t really make sense to me but that’s how I’m interpreting my textbook.
There is no physical theory or no physical law saying that internal energy cannot be negative.
So what is the problem of having negative internal energy?

It seems that you are causing your own confusion. I am sorry if I am misinterpreting your queries.
1
#7
(Original post by Eimmanuel)
There is no physical theory or no physical law saying that internal energy cannot be negative.
So what is the problem of having negative internal energy?

It seems that you are causing your own confusion. I am sorry if I am misinterpreting your queries.
Wait. So internal energy can be negative. That makes it so much easier.

I was pretty much causing my own confusion by reading too much into one sentence of my text book.

Thanks!
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2 years ago
#8
(Original post by Snoozinghamster)
Wait. So internal energy can be negative. That makes it so much easier.

I was pretty much causing my own confusion by reading too much into one sentence of my text book.

Thanks!
I am not sure what is the sentence in the textbook that is causing the confusion.

As I have provided a link above for absolute zero and I would place it below again.
https://ipfs.io/ipfs/QmXoypizjW3WknF...lute_zero.html

I suggest that you give a read to get a general idea.
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#9
(Original post by Eimmanuel)
I am not sure what is the sentence in the textbook that is causing the confusion.

As I have provided a link above for absolute zero and I would place it below again.
https://ipfs.io/ipfs/QmXoypizjW3WknF...lute_zero.html

I suggest that you give a read to get a general idea.
Thanks I will give it a read.

The text book said that even at absolute zero the internal energy was not zero,
I read that as it could never be zero thus could never be less than zero. But now I get that it can!
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