A sample of gas is cooled from 273°C to 0°C. Which of the following statements accurately describes the sample at its new conditions?
1) The kinetic energy is now nearly zero.
2) The average velocity is now twice as fast.
3) The average velocity is half as fast.
4) The average kinetic energy is halved.
5) The average velocity is about two thirds of the original.

Question

Quizplus · Accepted Answer

The average kinetic energy of a gas is directly proportional to its absolute temperature (in Kelvin). When the gas is cooled from 273°C (546 K) to 0°C (273 K), its temperature is halved, which means its average kinetic energy is also halved (4). Since kinetic energy is related to the square of the velocity, a reduction in kinetic energy does not directly halve the velocity, but it does significantly reduce it, making (5) a reasonable approximation given the nature of kinetic energy and velocity relationship.

A Sample of Gas Is Cooled from 273°C to 0°C