Important Laws of Chemistry
Beer's Law:
States that in photo chemistry the proportion of light absorbed by a solution depends on the thickness of the absorbing layer and on the concentration of the absorbing substance in the solution.
A = ε × c × l
Boyle's Law:
States that the volume (V) of a given mass of gas at a constant temperature is inversely proportional to its pressure (p), that is, pV= constant. This means that if a gas is compressed three fold its volume is reduced by two-thirds.
Boyle (1627-90) was the first to define an element as a substance that cannot be broken down into something simpler by a chemical process.
Charles’s Law:
States that under constant pressure the volume of a fixed mass of gas varies directly with its absolute temperature. The absolute temperature is that measured from absolute zero, about -273° on the Celsius scale. In other words, the pressure of a gas increases by 1/273 of its volume at 0°C for every 1°C rise in temperature.
In other words, if the pressure of a gas remains constant, the volume of a gas increases by 1/273 of its volume at 0°C for every 1°C rise in temperature. Alternatively, at constant pressure the volume of a given mass of gas is directly proportional to the absolute temperature.
The principle was formulated by the French scientist, Jacques Alexander Charles.
Faraday's Law of Electrolysis:
States that (i) The amount of decomposition during electrolysis is proportional to the quantity of current passed, and (ii) For the same quantity of electricity passed through different solutions, the extent of decomposition is proportional to the chemical equivalent of the element or group liberated. The law was formulated by an English chemist, Michael Faraday (1791-1867).
Gay-Lussac's Law:
(i) Law of Gaseous Volume: States that when gases combine chemically, the volumes of the reactive gases and gaseous products are in simple proportion at the same temperature and pressure. In other words, when gases combine they do so in volumes which are in a simple ratio to each other, and to that of the product, if it is also gaseous. For example: One volume of nitrogen combines with three volumes of hydrogen to form two volumes of Ammonia.
(ii) Law of Thermal Expansion: It states that at constant pressure all gases expanded by the same amount for the same increase in temperature.
These laws were formulated by a French chemist, Joseph Lois Gay-Lussac (1778-1850).
Hess' Law:
States that the heat exchange in a chemical reaction is the same, no matter whether the reaction takes place in one stage or more. The principle was formulated by a German chemist Henri Hess (1802-50).
Graham's Law of Diffusion:
States that the rate at which two gases diffuse is inversely proportional to their densities. It means that the lighter the gas, the faster it will diffuse through any medium. The law was defined by a Scottish chemist, Thomas Graham (1805-60).
Henry's Law:
States that the mass of a gas which is dissolved in a given volume of liquid at constant temperature is directly proportional to the pressure of the gas. It applies to gases that do not react with the liquid (solvent). The principle was formulated in 1803 by the British chemist William Henry.
Lambert's Law:
States that layers of equal thickness of homogeneous material for example, coloured filter absorb equal proportion of light.
Raoult's Law:
States that the lowering of the vapour pressure of a solvent by a solute (dissolved substance) is proportional to the MOLE fraction of the solute - the proportion of solute molecules to the total number of molecules, solute and solvent present. Since the lowering of vapour pressure causes an elevation of the boiling point and a depression of the freezing point, it is used to determine the molecular mass of a solute. The law is named after the French chemist, Francois Marie Raoult (1840-1901)
Law of Conservation of Mass and Matter:
Matter can neither be created nor destroyed. The sum total of mass or matter for a system always remains constant without any increase or decrease in quantity.
