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# Is potential energy of a gas constant with changing temperature?

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1. I know that an increase in temperature causes an increase in kinetic energy but I can't find out if there's any link between temperature and potential energy.
2. (Original post by ashlingm)
I know that an increase in temperature causes an increase in kinetic energy but I can't find out if there's any link between temperature and potential energy.
For what kind of gas? If you're thinking of an ideal gas, then it has no internal potential energy - all of it is kinetic. So whenever you heat an ideal gas, all of the thermal energy goes to increasing the kinetic energy (and thus the temperature) of the gas.

An ideal gas has no internal potential energy as we assume that there are no attractive inter-molecular forces. Consider lifting a mass at constant speed from the ground. At a height , you have used up J of energy to lift the mass. That energy is now stored in the gravitational field; the mass has potential energy, due to its position above the ground. That's because you have transferred energy to it by doing work against the attractive force of gravity.

Similarly, if two gas molecules are close together, and attract each other, then it will cost energy to move them apart against the attractive force, and that energy will be stored in the force field as potential energy. But if they don't attract each other when close (like an ideal gas), they can move further apart at no cost of energy.

So for a real gas (where the molecules do attract when close), then added heat energy is shared between the kinetic and the potential energy of the molecules.

The link, by the way, is between temperature and KE. Temperature is proportional to the mean square speed of the molecules of the gas.
3. Perfect, thank you! I think I was getting ideal gases mixed up with other questions and I got slightly muddled.
(Original post by atsruser)
For what kind of gas? If you're thinking of an ideal gas, then it has no internal potential energy - all of it is kinetic. So whenever you heat an ideal gas, all of the thermal energy goes to increasing the kinetic energy (and thus the temperature) of the gas.

An ideal gas has no internal potential energy as we assume that there are no attractive inter-molecular forces. Consider lifting a mass at constant speed from the ground. At a height , you have used up J of energy to lift the mass. That energy is now stored in the gravitational field; the mass has potential energy, due to its position above the ground. That's because you have transferred energy to it by doing work against the attractive force of gravity.

Similarly, if two gas molecules are close together, and attract each other, then it will cost energy to move them apart against the attractive force, and that energy will be stored in the force field as potential energy. But if they don't attract each other when close (like an ideal gas), they can move further apart at no cost of energy.

So for a real gas (where the molecules do attract when close), then added heat energy is shared between the kinetic and the potential energy of the molecules.

The link, by the way, is between temperature and KE. Temperature is proportional to the mean square speed of the molecules of the gas.

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