Question

Two substances, A and B, react with each other in such a way that A is 50% consumed in 33 minutes and 75% consumed in 66 minutes. Changing the concentration of B has no effect on the result. The reaction is:

A) first order in both A and B

B) first order in A and zero order in B

C) zero in both A and B

D) zero order in A and first order in B

E) second order in A an zero order in B

Answer 1

Let the rate of the reaction be

Rate = K * [A]^x * [B]^y

Since the rate of the reaction is not altered by changing the concentration of B implies that the value of y must be zero, in that case [B] doesn't alter the rate of the reaction

Hence the reaction must be zero order in B

Similarly, Let the reaction be zero order in A, it can't be otherwise the reaction wouldn't have taken independent of concentration

Let the reaction wrt A be first order

ln(Ao/At) = kt

at t==33 minutes

ln2 = k * 33

k = ln2/33

at t==66 minutes

ln4 = k * 66

k = ln2/33

Hence the value of K is same therefore the reaction must be first order wrt A

Hence the correct answer is First order in A and zero order in B

Therefore, the correct answer is Option B