Avogadro stated that equal volume of all the gases under similar conditions of temperature and pressure contain equal number molecules. This statement is called Avogadro’s hypothesis.

According Avogadro’s law

  • Avogadro’s number: The number of molecules present in a 1g mole of a gas is defined as Avogadro’s number.

NA = 6.023 X 1023 per gram mole

  • At STP or NTP (T = 273 K and p = 1 atm 22.4 L of each gas has 6.023 x 1023 molecules.
  • One mole of any gas at STP occupies 22.4 L of volume.


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