An ideal gas is a system of identical particles in disordered motion that do not interact with each other. It is a model: in a real gas the particles interact via electrostatic-type forces, but these forces become negligible when the gas is rarefied and far from condensation. The only thing the molecules of an ideal gas can do is move in a straight line until they hit a wall or another molecule, bouncing elastically.
The key idea is captured in one sentence: ideal = no interaction between particles. This single assumption has an enormous consequence, which we will exploit throughout the chapter: if the particles do not interact, there is no potential energy of interaction, and so all of the gas’s energy is kinetic energy of agitation.
Principle — Ideal gas
An ideal gas is a collection of identical particles in disordered motion that do not interact with each other. Pressure arises only from collisions with the walls; the internal energy is purely kinetic.
Pressure, in this picture, is generated by the particles’ collisions with the walls of the container: the faster the particles (high temperature) and the more numerous they are (high density), the greater the pressure. This is the microscopic picture that replaces the macroscopic idea of the gas “pushing”.
Microscopic model of a gas: the particles move in random directions at different speeds. Pressure is generated by the collisions with the walls.
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Topics: Teoria cinetica dei gas Concepts: Legge dei gas perfetti Skills: Interpretazione micro-macro
Related exercises: Problema — Moli e molecole in una bombola · Problema — Temperatura che raddoppia la pressione · Problema — Ranking di pressioni per temperatura