aP+bQ→ products, when [P] is doubled keeping [Q] constant and rate increases 2 times, when [P] is constant and [Q] is doubled and rate increases four times. The overall order is
For a reaction, aP+bQ→Products r=K[P]a[Q]b...........(i) 2r=k[2P]a[Q]b..........(ii) 4r=k[P]a[2Q]b ............(iii) On dividing Eqs. (ii) by (i) we get 2=2a⇒a=1 On dividing Eqs. (iii) by (i), we get 4=2b⇒b=2 ∴ Overall order =a+b=1+2=3.