# Does the total energy in a volume (gas) increase linearly with increases in pressure?

If a volume has a certain pressure, then double that pressure at another time, is the total energy stored doubled? I'm sure this has to do with thermodynamics and if I remember correctly there is a relationship relating temperature to energy, but not pressure (and obviously temp and pressure are related)

Edit - I should add I'm talking about a volume of gas

• Volume of what? – Bob D May 11 at 9:48
• That very depend on compressibility of the system. One of energy storage technology is storing of compressed air. Storing energy by water compression is useless. – Poutnik May 11 at 19:25

## 2 Answers

For an ideal gas you have the following result: U=3/2 pV. So for a fixed volume V If you increase the pressure then the internal energy U will increase linearly with p. See https://en.m.wikipedia.org/wiki/Ideal_gas

At pressures up to a few atmospheres most gases depart little from ideal gas behaviour. This answer is based on the ideal gas assumption.

I'll Suppose that you double the pressure by pumping more gas into the same container. If you then seal the container and leave it, the pressure is likely to drop, because most methods of pumping raise the temperature of the gas, and this will gradually fall as heat is lost to the surroundings. If you pump in more gas until the pressure is double at the same temperature as the original gas in the container then the energy stored will indeed be double. This because the pressure p of a volume V of gas at kelvin temperature T is given by$$pV=nRT$$ in which n is the number of moles of gas and $$R$$ is a constant. So by doubling the pressure, keeping temperature and volume the same, you have doubled the number of moles. But the internal energy of the gas is given by $$U=n c_v T$$ in which $$c_v$$ is a roughly constant for a gas (except at very low temperatures). So doubling the number of moles doubles the stored energy if the temperature is the same. This makes sense because at a given temperature each molecule has the same mean (kinetic) energy