6) A and B react stoichiometrically (i.e. one mol of A reacts with one mol of B)

Question

6) A and B react stoichiometrically (i.e. one mol of A reacts with one mol of B) to form P. If 0.01 M A and 10 M B are mixed, it is found that the log of the concentration of A vs. time is a straight line. a) Enter the order of the reaction with respect to A a) Enter the order of the reaction with respect to A (example, fifth-order) b) Enter the number of the one-line mechanism that is consistent with the kinetics and stoichiometry 4.2A P c Enter the order with respect to B according to the mechanism in b). (example, fifth-order) d) The half-life for the disappearance of A is 100 s. Enter the predicted half-life in seconds if the concentration of B is changed from 10 M to 20 M. Use two significant figures and do not enter units.

Explanation / Answer

since A is 0.01M and B is 10M, the high concentration ratio of B to A suggest the reaction to be pseudo order

rate R= K[A] [B]

since [B] is very high

R= K' [A]

-dCA/dt= K' [A]

logA= logA0- kt

where A= concentration at any time t and AO is initial concentration and t = time   (so the reaction is first oder with respect to A)

the mechanism for first order is A--->P (2 is correct answer)

Sine B does not undergo any change its order is zero

Half life for the given reaction is 100s

K'= 0.693/100

K[A] = K'

K= K'/[A] =0.693/(100*10)= 0.000693

When [A] is changed to 20M

K'= K*[A] =0.000693*20=0.01386

K' =0.693/ half life

Half lfife= 0.693/0.01386=50

Rate constnat= 0.000693 M/s

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