Published On: Sun, Jun 20th, 2010

Chemistry-Important Laws in Chemistry

Boyle’s Law

It states that when any gas is expanded or compressed at constant temperature, its volume (V) and pressure (P) are inversely proportional to each other.

P ∞ 1/V (or) PV = constant

Charle’s Law

It states that when any gas is expanded or compressed at constant pressure, its volume (V) is directly proportional to its absolute temperature T.

V ∞ T (or) V/T = contant (or) V1/T1 = V2/T2

Dalton’s Law of Partial Pressure

It states that the total pressure exerted by a mixture of different gases in a given space is equal of sum to partial pressure of each constituent gas where partial pressure of a gas is the pressure exerted by it, if it were to occupy the same space alone.

P = P1 + P2 + P3 +…

Law of Indestructibility

It states that matter can neither be created nor destroyed by any chemical change.

Law of Multiple Proportion

It states that when two elements combine to form more than one compound, the mass of one which combines with the fixed mass of the other bears a simple ratio to each other.

Law of Reciprocal Proportion (or Law of Equivalent Proportions)

It states that when two different elements combine with the same weight of third element the ratio in which they do so will be the same or some multiple of the ratio in which they combine with each other, e.g., The elements C and H combine with the third element O to form CO2 and H20. Also they combine directly to form CH4 :

In CO2 ⇒ C : = 12 : 32 = 3 : 8
In H2O ⇒ H : O = 2 : 16 = 1 : 8

i.e., from this the ratio C : H = 3 : 1, Now in,

CH4 ⇒ C : H = 12 : 4 = 3 :1

Law of Constant Composition

It states that a chemical compound always consists of same elements combined together in the same proportion by mass.

Gay Lussac’s Law of Combining Volumes

It states that gases react together in volumes which bear simple and whole number ratios to one another as well as to the volumes to the gaseous products whereas the volumes being measured under same conditions of temperature and pressure.

Law of Mass Actidon

It states that the rate of chemical reaction is proportional to the molecular concentration of each of reacting constituents.

Faraday’s Law of Electrolysis

  1. The products of electrolysis appear only at the electrodes, having weight proportional to the quantity of electricity passed.
  2. The amounts of ions liberated at the various electrodes are proportional to their chemical equivalents when current passes through the different electrolytes.

Ohm’s Law

It states that the magnitude of current flowing between two ends of a conductor is proportional to the potential difference between them.

Avogadro’s Law

It states that under similar conditions of temperature and pressure equal volume of all gases contain equal number of molecules.

Raoult’s Law

It states that the vapour pressure of a solution containing non – volatile solution is directly proportional to the mole fraction of the solvent.

PA = P°A . XA, PB = P°B . XB, ΔHmix = +ive, ΔV = +ive

The solutions which obey Raoult’s law are called Ideal Solutions

  1. When solvent – solvent and solute – solute interactions are stronger than solvent – solute interaction positive deviations take place.
    PA > P°A . XA, PB < P°B . XB, ΔHmix = +ive, ΔV = +ive
  2. When solvent – solvent and solute – solute interactions are weaker than solvent – solute interaction negative deviation takes place.
    PA < P°A . XA, PB < P°B . XB, ΔHmax = -ive, ΔV = -ive

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