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Kinetic Theory Of Gases




1. Gas Laws


    Gas laws are study of any two of quantities like pressure, volume and temperature, when the third is kept constant

    A. Boyle's law

  • "At constant temperature, the volume of a given mass of gas is invesely propertional to pressure." Thus
                   V ∝ 1/P
    Or,                PV = constant               (1)
  • If P1, V1are initial pressure and volumes and P2, V2be final values then,               
         P1V1= P2V2                    
  • Graph between P and V at temperature T1 and T2 such that T1<T2 are shown below,

    Boyle's law
  • Graph above shows that Boyle's law is strictly not obeyed by gases at all values of P and T but it obeys this law only at low pressure and high temperature i.e., at law density
B. Charle's Law
  • Charle's Law is stated as follows :
    "When pressure of a gas is constant the volume of a given mass of gas is directly proportional to its absolute temperature".
                   V/T = Constant               (2)
  • Graph between V and T is

    Charle's Law
    This graph shows that experimental graph deviates from straight line. Theoritical and enperimental graphs are in agreement at high temperature.




2. Ideal gas equation


  • We can combine Boyle’s law eqn (1) and charle’s law eqn (2) in to a single eqn i.e.,
         PV/T = Constant          (3)
    If n moles is the mass of gas then we write
         PV = nRT               (4)
    where, n is number of moles of gas, R=NAKB is the universal constant known as gas constant and T is the absolute temperature.
  • A gas satisfying eqn (4) at all values of presserves and temperatures is said to be an ideal gas
    now no of moles of gas
         n = m/M = N/NA
    where
         m - mass of gas containing N molecules
         M - molar mass
         NA - Avagadro’s number.
    From this,
         P = ρRT/M
         ρ - mass density of gas.



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