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Formula For Avogadro Law

Chemistry Formulas

Definition of Avogadro’s Law

It states that equal volume of all gases at same pressure and temperature contain equal number of molecules. We know that 1 mole contains 6.023 × 1023 molecules (a number called as Avogadro Number). It is obvious that if two gases contain equal number of molecules, they must also contain the same number of moles. So, at given temperature and pressure, the volume of any gas is also proportional to the number of moles. 

Avogadro's law, also known as the Avogadro hypothesis or Avogadro's principle, is a gas law that states that the total number of atoms/ molecules of gas (i.e. the amount of gaseous substance) is directly proportional to the volume occupied by the gas at normal temperatures and pressure.

Avogadro's law: v/n = k (where k is the proportionality constant)

When amount of gas increase, the corresponding increase in volume of the gas can be calculated with the help of the following formula:

v1/n1 = v2/n2

Derivation of Avogadro's Law

This Law  derived from the ideal gas equation, which can be expressed as follows:

PV = nRT

Where, P is the pressure exerted by the gas

V is the volume occupied by the gas

n is the amount of gaseous substance (number of moles of gas)

R is the universal gas constant

T is the absolute temperature of the gas

Rearranging the ideal gas equation, the following equation are as follows:
V/n = (RT)/P
Here, the value of (RT)/P is a constant 
V/n = k
Thus, the proportionality between both the volume occupied by a gas and the number of gaseous molecules is verified.

Solved example of Avogadro’s Law


“Equal volume of all gases at the same temperature and pressure contain equal number of particles.” This statement is a direct consequence of :

A.Avogadro’s law 

B.Charle’s law

C.ideal gas equation of particle pressure

Ans: Correct option is A. i.e. Avogadro’s Law

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