a) Given the initial concentration of each of the reactants, calculate the final

Question

a) Given the initial concentration of each of the reactants, calculate the final concentrations of A, B, and C. Assume the reaction goes to completion. [A]initial= 5.0 x 10^-7 M [B]initial= 7.0 x 10^-4M [C]initial= 0

b) Which reagent is in large excess? Is it reasonable to say that the concentration of this reagent is a constant?

c) How might you rewrite the rate law to show that the rate of the reaction, run under the conditions given in question 2a, depends upon the concentration of only one reactant?

d) The rate of the above reaction (using the initial reagent concentrations given above) was studied monitoring the concentration change of reactant A. A summary of the data obtained from that study is given below. Based on these experiemntal results, what is the order of the reaction with respect to this reactant? Given this new info, rewrite the rate law derived in question 2c.

graph one: [reactant] vs. time is a graph of a downward sloping curve, approaches zero as time goes on.

graph two: ln[reactant] vs. time is a graph of a less dramatic downward sloping curve, approaches zero as time goes by

graph three: 1/[reactant] vs. time is a graph of a straight line with a positive slope.


a) Given the initial concentration of each of the reactants, calculate the final concentrations of A, B, and C. Assume the reaction goes to completion. [A]initial= 5.0 x 10^-7 M [B]initial= 7.0 x 10^-4M [C]initial= 0

b) Which reagent is in large excess? Is it reasonable to say that the concentration of this reagent is a constant?

c) How might you rewrite the rate law to show that the rate of the reaction, run under the conditions given in question 2a, depends upon the concentration of only one reactant?

d) The rate of the above reaction (using the initial reagent concentrations given above) was studied monitoring the concentration change of reactant A. A summary of the data obtained from that study is given below. Based on these experiemntal results, what is the order of the reaction with respect to this reactant? Given this new info, rewrite the rate law derived in question 2c.

graph one: [reactant] vs. time is a graph of a downward sloping curve, approaches zero as time goes on.

graph two: ln[reactant] vs. time is a graph of a less dramatic downward sloping curve, approaches zero as time goes by

graph three: 1/[reactant] vs. time is a graph of a straight line with a positive slope.

Explanation / Answer

a) The reaction will be A + B -> C

Since the ratio of reactant A and B is 1:1. Hence the element whose number of moles are less will be the limiting reagent for the rxn.

In this rxn,. [A]initial= 5.0 x 10^-7 M [B]initial= 7.0 x 10^-4M, hence B used will be equal to 5*10^(-7) since whenever A is finished, then the rxn can't proceed in forward direction.

Excess Reagent = B

Excess = 7*10^(-4)/5*10^(-7) = 1400

Hence, B is present in excess in the reaction

For the final concentrations for [A] and [C], you should have derived that [A]final = [C]final = 5.0 x 10^-7 M.

d) Look for the graph that contains the straight line..which will be graph three. From the information you have given, 1/[reactant] vs. time, this indicates a second-order reaction.

To finish the question, use the rate law you have rewritten for question (c). If I am not mistaken, the rewritten rate law from (c) will be rate = k[B]^b. Since [B] will be in excess, the concentration remains unchanged; therefore, [B]initial = [B]final.

So rate = k[B]^2 or
rate = k[7.0 x 10^-4]^2

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