气体分子运动论Kinetic theory of gases

气体由大量做无规则直线运动的分子组成；分子本身的体积与容器体积相比可忽略；除碰撞外分子之间没有作用力；碰撞是完全弹性的；分子的平均动能与热力学温度成正比，Ē = (3/2)kT。满足这些假设的气体称为理想气体。

A gas consists of many molecules moving randomly in straight lines; their own volume is negligible compared with the container; there are no forces between them except in collisions; collisions are perfectly elastic; and their average kinetic energy is proportional to the thermodynamic temperature, Ē = (3/2)kT. A gas meeting these assumptions is ideal.

高压时分子本身体积不可忽略，低温时分子间吸引力变得重要，实际气体偏离理想行为。范德华方程通过修正体积和压强描述实际气体。分子小、分子间作用力弱的气体（如 He、H₂）在高温低压下最接近理想气体。

At high pressure the molecules' own volume matters, and at low temperature intermolecular attractions become important, so real gases deviate from ideal behaviour. The van der Waals equation corrects the volume and pressure to describe them. Gases with small molecules and weak forces, such as He and H₂, behave most ideally at high temperature and low pressure.

麦克斯韦–玻尔兹曼分布给出了气体分子速率的统计分布：温度升高时分布曲线变宽、峰值右移，高速分子比例增大，这也解释了升温使反应加快的原因。

The Maxwell–Boltzmann distribution gives the statistical spread of molecular speeds: as temperature rises the curve broadens and its peak moves to higher speed, with more fast molecules, which also explains why reactions speed up when heated.