Microscopic and Macroscopic Description of Gases

Thermodynamics usually deals with large-scale properties such as: Pressure `p` Volume `V` Temperature `T` Internal energy `U` These quantities describe the gas as a whole. Statistical mechanics connects these observable properties with enormous numbers of microscopic particles. At microscopic level, gas molecules: move continuously; have different velocities; collide with one another; collide with container walls; possess kinetic energy. We cannot practically follow every molecule separately in a normal gas. Instead, statistical mechanics uses quantities such as: average kinetic energy mean-square speed root-mean-square speed to predict macroscopic behaviour. *Microscopic molecular behaviour → statistical averaging → macroscopic properties**

Conceptually: **Microscopic particle motion → averages → p, V, T and U**