gasses

Gases are one of the fundamental states of matter. They have indefinite shape and volume, expanding to fill the space available. Gases generally have low density compared with liquids and solids and are highly compressible. The particles are far apart and move rapidly in random directions, colliding with each other and with container walls.

Kinetic theory describes gases as particles in constant, random motion. Pressure arises from particle collisions with container surfaces. Temperature measures the average kinetic energy of the particles; increasing temperature raises the tendency to spread and, at a given volume, can raise pressure.

Gas laws describe relationships among pressure, volume, temperature, and amount of substance. Boyle's law states that, at constant temperature and amount, pressure and volume are inversely related. Charles' law relates volume to temperature at constant pressure. Avogadro's law states that equal volumes of gases at the same temperature and pressure contain equal numbers of particles. The ideal gas law, PV = nRT, combines these ideas for gases under conditions where intermolecular forces are small; real gases deviate from this behavior at high pressure or low temperature, described by a compressibility factor Z.

Mixtures of gases follow Dalton's law of partial pressures: the total pressure is the sum of the partial pressures of each component. Gases can diffuse and effuse, with rates influenced by molecular mass. Common examples include nitrogen, oxygen, argon, carbon dioxide, and noble gases; the Earth's atmosphere is a complex mixture of several gases.

Gases have broad applications in science and industry and pose safety and environmental considerations, including flammability, toxicity, and greenhouse effects. Measurements use units such as pascals, liters, kelvin, and the gas constant R.