How does potential energy change during phase change from liquid to ideal gas?

I understand during a phase change from a liquid to a real gas, the potential energy of the system increases. However, what happens when a liquid turns into an ideal gas. I understand that the internal energy is increasing since heat is being applied, however since the kinetic energy of the molecules doesn't increase (since temperature is constant) this must mean that the potential energy of the system increases since internal energy = KE + PE

However, the potential energy of the system can't increase in an ideal gas because the potential energy is 0. So how does this work?

Reply 1

Absent Agent

21

Original post by Jpw1097

I understand during a phase change from a liquid to a real gas, the potential energy of the system increases. However, what happens when a liquid turns into an ideal gas. I understand that the internal energy is increasing since heat is being applied, however since the kinetic energy of the molecules doesn't increase (since temperature is constant) this must mean that the potential energy of the system increases since internal energy = KE + PE

However, the potential energy of the system can't increase in an ideal gas because the potential energy is 0. So how does this work?

In your first sentence you consider PE as K.E. When a liquid turn turns into an ideal gas the internal energy is certainly increasing as the temperature is increasing, this is one of the assumption of an ideal gas.

Reply 2

PhysicsMathsTut

10

Original post by Jpw1097

I understand during a phase change from a liquid to a real gas, the potential energy of the system increases. However, what happens when a liquid turns into an ideal gas. I understand that the internal energy is increasing since heat is being applied, however since the kinetic energy of the molecules doesn't increase (since temperature is constant) this must mean that the potential energy of the system increases since internal energy = KE + PE

However, the potential energy of the system can't increase in an ideal gas because the potential energy is 0. So how does this work?

All of those are correct. Just remember that P.E. is negative. It increases and becomes zero for an ideal gas.

Reply 3

langlitz

17

Original post by Jpw1097

I understand during a phase change from a liquid to a real gas, the potential energy of the system increases. However, what happens when a liquid turns into an ideal gas. I understand that the internal energy is increasing since heat is being applied, however since the kinetic energy of the molecules doesn't increase (since temperature is constant) this must mean that the potential energy of the system increases since internal energy = KE + PE

However, the potential energy of the system can't increase in an ideal gas because the potential energy is 0. So how does this work?

The problem is that you can't have a liquid turning into an ideal gas. An ideal gas does not have a critical point so no matter how much you compress it it will not condense into a liquid. It's alot more complicated than you are thinking it is

How does potential energy change during phase change from liquid to ideal gas?

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