Gas Laws

Gas laws
Assuming permanent gases to be ideal, through experiments, it was established that gases
irrespective of their nature obey the following laws.
Boyle’s Law
At constant temperature the volume (V) of given mass of a gas is inversely proportional to its
pressure (p), i.e.,
V ∝ 1/p ⇒ pV = constant
For a given geas, p V = p V
Charles’ Law
At constant pressure the volume (V) of a given mass of gas is directly proportional to its absolute
temperature (T), i.e.,
V ∝ T ⇒ V / T = constant
For a given gas, V /T = V /T
At constant pressure the volume (V) of a given mass of a gas increases or decreases by 1/273.15 of
its volume at 0°C for each 1°C rise or fall in temperature.
Volume of the gas at t°Ce
V = V (1 + t/273.15)
where V is the volume of gas at 0°C.
Gay Lussacs’ or Regnault’s Law
At constant volume the pressure p of a given mass of gas is directly proportional to its absolute
temperature T, i.e. ,
p ∝ T ⇒ V/T = constant
For a given gas,
p /T = p /T
At constant volume (V) the pressure p of a given mass of a gas increases or decreases by 1/273.15
of its pressure at 0°C for each l°C rise or fall in temperature.
Volume of the gas at t°C, p = p (1 + t/273.15)
where P is the pressure of gas at 0°C.
Avogadro’s Law
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
(i) Avogadro’s number The number of molecules present in 1g mole of a gas is defined as
Avogadro’s number.
N = 6.023 X 10 per gram mole
(ii) At STP or NTP (T = 273 K and p = 1 atm 22.4 L of each gas has 6.023 x 10 molecules.
(iii) One mole of any gas at STP occupies 22.4 L of volume.