At elevated temperature, HI decomposes according to the chemical equations:
`2HI(g) to H_(2)(g) + I_(2)(g)`

a)Determine (i) the order of reaction and (iii) Write the rate expression.
b) Calculate the rate constant and give its units.

Explanation

From this data, it is quite evident that when (HI) is increased from 0.005 to 0.01 (made twice),
rate = `(30 xx 10^(-4))/(7.5 xx 10^(-4)) =4`
When (HI) is increased from 0.01 to 0.02 (made twice),
rate `= (12 xx 10^(-3))/(3 xx 10^(-3)) =4`
a) `therefore` Order of reaction=2
Rate expression, (r)=`k[HI]^(2)`
b) Calculation of rate constant:
For expt. (1), `k(0.005 mol L^(-1))^(2)=(7.5 xx 10^(-4)mol^(-1)s^(-1)`
`k=(7.5 xx 10^(-4) mol L^(-1)s^(-1))/(2.5 xx 10^(-5)mol^(2)L^(-2))=30 mol^(-1)Ls^(-1)`.