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,
  
  
  
• 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
  

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

• 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=N_AK_B 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/N_A
  where
       m - mass of gas containing N molecules
       M - molar mass
       N_A - Avagadro’s number.
  From this,
       P = ρRT/M
       ρ - mass density of gas.