分子運動論と気体の状態方程式

According to kinetic molecular theory, gas pressure results from the impact of constantly moving particles colliding with container walls. The pressure depends directly on the number of molecules hitting a unit area per unit time. As gas particles move rapidly and collide with surfaces, they exert force, creating measurable pressure that increases with more frequent and forceful collisions.

When volume decreases while temperature and moles remain constant, gas particles are forced closer together, reducing interparticle spacing. This increases gas density and collision frequency—the rate of molecule-wall collisions. More frequent collisions with container walls result in greater pressure, demonstrating the inverse relationship described by Boyle's law.

When temperature increases, the average kinetic energy of gas particles increases proportionally. Particles collide more frequently and forcefully with container walls. If volume is held constant, these increased collisions raise pressure directly, as described by Gay-Lussac's law, showing the direct proportional relationship between temperature and pressure.

Adding more moles of gas increases gas density and collision frequency. To maintain constant pressure, the volume must expand proportionally to spread collisions over a greater surface area. This direct relationship between volume and moles is expressed by Avogadro's law, which states that equal volumes contain equal numbers of molecules at identical conditions.

When temperature increases at constant pressure, gas particles move faster and collide more forcefully. To prevent pressure from rising, volume must expand, increasing the average distance molecules travel to reach walls and the wall surface area. These changes decrease collision frequency per unit area, balancing the effect of increased collision force from higher kinetic energy.

In gas mixtures, molecules of different gases act independently due to large distances between them. Each gas bombards container walls with the same frequency whether other gases are present or not. The total pressure equals the sum of individual partial pressures, as stated by Dalton's law, since gas components do not attract or repel one another.

Kinetic molecular theory assumes gas particles have negligible volume compared to container volume, move randomly in straight lines, and undergo perfectly elastic collisions. Crucially, gas particles do not attract or repel one another, allowing them to behave independently. These assumptions enable the theory to explain observed gas behavior and derive all major gas laws.