Question

Consider the nonenzymatic elementary reaction A + B → C. When the concentrations of A and B are each 25.0 mM, the reaction velocity is measured as 4.11 µM C produced per minute.

Calculate the rate constant for this reaction with units!.

What is the molecularity of the above reaction?

If this reaction is in zero order kinetics how long would it take to produce 2.25 x 10^-3 moles of C from a starting concentration of reactants A and B of 100.0 mL of a 125 mM solution of each present?   Assume the rate constant determined above is the same rate constant at zero order kinetics, just units are changed on the rate constant to those for a zero order reaction.

If the reaction was in first order kinetics instead of zero order kinetics, how long would it take to produce 2.25 x 10^-3 moles of C from a starting concentration of 125 mM of each reactant and 100.0 mL volume? Assume the rate constant determined above in a, is the same rate constant at first order kinetics, just units are changed to reflect a first order rate constant.

Answer 1

Consider the nonenzymatic elementary reaction A + B → C. When the concentrations of A and B are each 25.0 mM, the reaction velocity is measured as 4.11 µM C produced per minute.

The rate = 4.11*10-6 M/s

The rate for elementary reaction= K[A] [B] = 4.11*10-6

K is rare constant

K[25*10^-3]*25*10^-3]= 4.11*10^-6

K= 4.11/625=0.0065/Mmin

The molecularity is the number of molecules participating =1+1=2

b) for Zero order reaction , CA= CAO-kt

where CA = Conentration of A at time

Moles of C formed= 2.25*10-3 moles of A reacted= 2.25*10-3

Moles of A remaining = moles of A initially- moles of A reacted=

Moles of A initally in 100m; = 125*10^-3*0.1L= 0.0125

Moles of remaining= 0.0125-2.25*10-3 =0.01025 moles

Concentration oF A= 0.01025/0.2= 0.05125

0.05125= 125*10^-3-0.0065t

0.0065t= 0.125-0.05125

t=11.34 minutes

C) for first order CA= CAO*e^(-kt)

0.05125=0.125e(-kt)

0.05125/0.125= e(-kt)

0.41= e(-kt)

-kt= 0.8916

t =0.8916/0.0065=137 minutes