Chemistry - Laws in Chemistry

avogadro's law

equal volumes of any two gases at the same temperature and pressure contain the same number of molecules.

boyle's law

the volume of a sample of gas at a given temperature varies inversely with the applied pressure

charles's law

the volume occupied by any sample of gas at a constant pressure is directly proportional to the absolute temperature

first law of thermodynamics

the change in internal energy of a system, ∆U, equals q + w (heat plus work)

graham's law of effusion

the rate of effusion of gas molecules from a particular hole is inversely proportional to the square root of the molecular weight of the gas at constant temperature and pressure

henry's law

the solubility of a gas is directly proportional to the partial pressure of the gas above the solution

hess's law

for a chemical equation that can be written as the sum of two or more steps, the enthalpy change for the overall equation equals the sum of the enthalpy changes for the individual steps

ideal gas law

the equation PV = nRT, which combines all of the gas laws

integrated rate law

a mathematical relationship between concentration and time

law of combining volumes

gases at the same temperature and pressure react with one another in volume ratios of small whole numbers

law of conservation of energy

energy may be converted from one form to another, but the total quantity of energy remains constant

law of conservation of mass

the total mass remains constant during a chemical change (chemical reaction)

law of definite proportions

a pure compound, whatever its source, always contains definite or constant proportions of the elements by mass

law of mass action

the values of the equilibrium-constant expression Kc are constant for a particular reaction at a given temperature, whatever equilibrium concentrations are substituted

law of multiple proportions

when two elements form more than one compound, the masses of one element in these compounds for a fixed mass of the other element are in ratios of small whole numbers

law of partial pressures

the sum of the partial pressures of all the different gases in a mixture is equal to the total pressure of the mixture

periodic law

when the elements are arranged by atomic number, their physical and chemical properties vary periodically

raoult's law

the partial pressure of a solvent, Pa, over a solution equals the vapor pressure of the pure solvent, P°a, times the mole fraction of solvent, Xa, in the solution.

rate law

an equation that relates the rate of a reaction to the concentrations of reactants (and catalyst) raised to various powers

second law of thermodynamics

the total entropy of a system and its surroundings always increases for a spontaneous process. Also, for a spontaneous process at a given temperature, the change in entropy of the system is greater than the heat divided by the absolute temperature

third law of thermodynamics

a substance that is perfectly crystalline at 0 K has an entropy of zero