Standard/ Class/ Grade XI ChemistryChapter 1 Basic ConceptsGurudatta K Wagh, [email protected]
Avogadro’s Law, Atomicity, Mole and Avogadro Number
Avogadro’s lawEqual volumes of all gases under identical conditions of temperature and pressure contain equal number of molecules
BasisMost gases exist as polyatomic molecules e.g. diatomic - hydrogen H2, oxygen O2, nitrogen N2, chlorine Cl2
Mathematical expression of Avogadro’s law
At constant pressure and temperature (STP-standard temperature 273.15 K and pressure 760 mm Hg) the volume of a gas is directly proportional to number of moleculesV α n, V/ n = constant R, number of moles ‘n’= mass of gas/ molar mass of gas
General gas equation PV = nRT. Therefore V/ n = RT/ PR = 0.08205 L atmosphere mol-1 K-1
V/ n = 0.08205 L atmosphere mol-1 K-1 X 273.15 K / 1 atmV/ n = 22.414 L mol-1 or 0.022414 m3 = Avogadro’s molar volume/ molar gas volume at STP
V α n, V/ n = constant R, number of moles ‘n’= mass of gas/ molar mass of gas
volume of a gas is directly proportional to number of molecules
AtomicityIt is the total number of atoms of constituent elements combined to form a molecule
H2(g) + Cl2(g) → 2HCl(g)
monatomic - inert gases
diatomic - oxygen, nitric oxide, hydrogen, etc.
triatomic - ozone, sulphur dioxide, carbon dioxide,etc.
polyatomic ions (containing more than 3 atoms) – phosphate, sulphur, etc.
molecules molecules moleculesHydrogen Chlorine Hydrogen chlorideX X 2X
Mole
One mole of a substance is the quantity of the substance equal to its atomic mass or molar mass in gram
One mole of a substance is defined as the amount of substance that contains the number of particles, atoms, molecules, ions or electrons, etc. as present in 0.012 kg of Carbon-12
1 mole = 6.022 X 1023 molecules = 22.414 L = 0.022414 m3
One mole of a substance is the quantity of the substance equal to its atomic mass or molar mass in gram
