Dalton's law states that the total pressure of the gas mixture in a container is equivalent to the sum of the partial pressures of the individual gases in that container. Dalton's law only refers to nonreacting gases and is related to the ideal gas law, which predicts how the pressure, volume and temperature of a gas is related to the amount of the gas present.
The partial pressure is calculated by taking the amount of gas, in moles; multiplying it by the universal gas constant and the temperature of the system; and then dividing it by the volume of the system. In the kinetic theory of gases, the molecules in a gas mixture expand to fill up the container, expanding so far apart that they act independently of each other. Thus, the pressure of an ideal gas is due to the interaction between the molecules and the container. In keeping with the ideal gas law, the pressure of this gas is influenced by the volume and temperature of the system, along with the amount of the gas in the container. Since the gases in a mixture are in the same container, they are exposed to the same temperature and volume, and since each gas exerts its own pressure in the system, these pressures can be added to find the total pressure of the system.