The initial concentrations of HI as 0.005,0.01,and0.02 mol/L, respectively, and the corresponding initial rates as given:
HI(molL−1)0.0050.010.02
Rate (molL−1s−1)7.5×10−43.0×10−31.2×10−2
For the reaction, rate law is
rate=k[HI]P
P is the order of the reaction.
From the given data
7.5×10−4=k[0.05]P-------(1)
3×10−3=k[0.01]P --------(2)
1.2×10−2=k[0.02]P ---------(3)
On dividing Equation (3) by equation (2)
3×10−312×10−3=k[0.01]Pk[0.02]P
⇒2P=22
⇒P=2