# Laws of chemistry and physics

All chemical reactions and physical transformations occur according to chemical and physical laws. The following is a list of the statements of some laws of particular importance in chemistry.

• Gas laws
• Law of perfect gases: relates the state functions quantity of substance, pressure, volume and temperature of a perfect gas to each other.
• Law of partial pressures: the total pressure exerted by an ideal mixture of ideal gases is equal to the sum of the partial pressures that would be exerted by the gases if they were present alone in an equal volume.
• Boyle-Mariotte law: under constant temperature conditions, the pressure of a gas is inversely proportional to its volume.
• Gay-Lussac’s First Law: under conditions of constant pressure, the volume of a gas increases linearly with increasing temperature.
• Gay-Lussac’s Second Law: under constant volume conditions the pressure of a gas increases linearly with increasing temperature.
• Van der Waals’ law: relates the state functions quantity of substance, pressure, volume and temperature of a real gas to each other.
• Henry’s Law: at constant temperature, the amount of gas passing into solution in a given liquid is directly proportional to the partial pressure of the gas in equilibrium with the liquid.
• Weight laws
• Law of conservation of mass or Lavoisier’s law: in a chemical reaction, the mass of the reactants is exactly equal to the mass of the products.
• Law of definite proportions or Proust’s law: in a given chemical compound in its pure state, the elements that form it stand among themselves in definite and constant mass proportions.
• Law of multiple proportions or Dalton’s law: when two elements combine in different ways to form different compounds, a certain mass of one element combines with masses of the other element that stand with each other in a ratio that can be expressed by simple fractions.
• Law of mass action: the rate of a chemical reaction is proportional to the concentration of the substances participating in it.
• Le Châtelier’s Principle: every system in equilibrium tends to react to a change imposed on it from outside by minimizing its effects.
• Raoult’s Law: relates the vapor pressure of a liquid in solution to its vapor pressure in its pure state and its concentration in terms of molar fraction.
• Hess’s Law: the change in enthalpy of a chemical reaction is independent of the intermediate pathway by which products are obtained from the reactants.
• Debye-Hückel’s Law: defines the average activity coefficient of electrolyte solutions.
• Law of independent mobility of ions: the equivalent conductance of a solution of an electrolyte at infinite dilution is equal to the sum of the mobility of the cation and anion from which the electrolyte is formed, mobilities that at infinite dilution do not affect each other.
• Lambert-Beer’s Law: relates the amount of light absorbed by a substance to its chemical nature, its concentration, and the thickness of the medium traversed.
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