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How would you calculate the order of the reaction 2NO_((g))+O_(2(g))rarr2NO_(2(g)) by an experiment ? (or) prove that 2NO+O_2rarr2NO_2 is a third order reaction.

Answer»

Solution :`2NO_((g))+O_(2(g))rarr2NO_(2(g))`
Series of EXPERIMENTS are conducted by keeping the CONCENTRATION of one of the reactants as constant and changing the concentration of the others.

Rate `=k[NO]^m[O_2]^n`
For experiment 1, the rate law is
`"Rate"_1= k [NO]^m[O_2]^n""...(1)`
`19.26xx10^(-2)=k[1.3]^m[1.1]^n`
For experiment 2
`"Rate"_2= k [NO]^m[O_2]^n""...(2)`
`38.40xx10^(-2)=k[1.3]^m[2.2]^n`
For experiment 3
`"Rate"_3= k [NO]^m[O_2]^n""...(3)`
`76.8xx10^(-2)=k[1.3]^m[2.2]^n`
`((2))/((1))IMPLIES(38.40xx10^(-2))/(19.26xx10^(-2))=(k[1.3]^m[2.2]^n)/(k[1.3]^m[1.1]^n)`
`2=((2.2)/(1.1))^n`
`2=2^nimpliesn =1 `
Therefore the reaction is FIRST order respect to `O_2`
`((3))/((2))implies(76.8xx10^(-2))/(19.26xx10^(-2))=(k[2.6]^m[1.1]^n)/(k[1.3]^m[1.1]^n)`
`4=((2.6)/(1.3))^n`
`4 =2^m implies m = 2`
Therefore the reaction is second order with respect to NO
The rate law is `"Rate "_1 =k[NO]^2[O_2]^1`
The overall order of the reaction = 2+1=3


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