So temperature is the kinetic energy of the atoms/molecules. When compressing a

Question

So temperature is the kinetic energy of the atoms/molecules. When compressing a gas, which is lowering the volume, don't the atoms/molecules collide with each other at more frequently? I get that this might cause them to bounce off each other faster and the walls of the container, which increases the temperature ..BUT wouldn't the atoms and molecules stick to each other more since they are hitting each other more frequently? Or is this not true because of "ideal gas", which doesn't have the atoms condensing or sticking together? Is there a case where you compress gas and the temperature decreases? any simple example? Thanks

Explanation / Answer

When a gas is compressed, work is done ON the gas molecules. That means that additional energy is transferred to the gas molecules from whatever is doing the compressing. It is the additional energy that increases the kinetic energy (KE) of the molecules. Since temperature is directly proportional to the KE of the molecules, the increase in KE means the temperature goes up. We're not really talking about any of the usual gas laws (Boyle's law, Charles's law, ideal gas equation, etc). Instead, the mathematical relationship in play is this: u = (3RT / M)^(1/2) .... where u is the RMS speed of the gas molecules and is therefore, proportional to kinetic energy, R is the gas constant (8.314 J/molK), T is the absolute temperature, and M is the molar mass. Since energy must be conserved, the energy transferred to the gas molecules increases the kinetic energy of the molecules and increases the temperature.

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