Physics A2 · Ideal gases. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
The kinetic theory explains the pressure of a gas by treating it as a very large number of tiny molecules in rapid random motion. The assumptions are: the molecules' own volume is negligible compared with the container, there are no forces between them except during collisions, all collisions are elastic, and the time of a collision is negligible.
When a molecule hits a wall and bounces back, its momentum changes, so the wall exerts a force on it and it exerts an equal force on the wall. Many such collisions each second on each unit of area give a steady pressure.
Comparing the result with pV = NkT shows that the mean translational kinetic energy of a molecule depends only on the thermodynamic temperature.
Students use the temperature in °C, or forget the square root and say that doubling the kelvin temperature doubles the r.m.s. speed. Always change to kelvin, and remember that it is the mean kinetic energy, not the speed, that is proportional to T.
Answer: About 390 m s−1.
Type what you are stuck on. The helper finds the explanation, worked examples and the notes to read, free and instant.