Consider the reaction mechanism below:
2 BF3 → B2F6 slow
B2F6 + NH3 → BF3 + F3BNH3 fast
a. What is the overall reaction that this mechanism is describing?
b. Which step is limiting?
c. What is the rate law for the overall reaction?
d. What is the intermediate compound involved in this reaction?
a. 2 BF3 → B2F6
B2F6 + NH3 → BF3 + F3BNH3
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2 BF3 + NH3 → BF3 + F3BNH3
b. The rate determining step is the slow step.
c.rate = k(BF3)^2( NH3)
d. The intermediate is the "compound" that is canceled when the equations are added; i.e., B2F6
a. The overall reaction that this mechanism is describing is:
2 BF3 + NH3 → BF3 + F3BNH3
b. In this mechanism, the second step (B2F6 + NH3 → BF3 + F3BNH3) is the limiting step because it is the slower step.
c. To determine the rate law for the overall reaction, we need to examine the slow step since it is the rate-determining step. From the slow step, we can see that the rate of the reaction depends on the concentration of BF3, therefore the rate law for the overall reaction would be:
Rate = k [BF3]^2 [NH3]
d. The intermediate compound involved in this reaction is B2F6. It is formed in the slow step and consumed in the fast step, but it does not appear in the overall reaction.
To determine the answers to these questions, we need to analyze the given reaction mechanism and its steps.
a. The overall reaction that this mechanism is describing can be determined by adding up the individual steps. In this case, the first step produces B2F6, and the second step consumes B2F6, resulting in the overall reaction:
2 BF3 + NH3 → BF3 + F3BNH3
b. To determine the limiting step, we need to compare the stoichiometry of the reactants and products in each step. In this mechanism, the first step involves the reaction of 2 BF3, while the second step involves the reaction of B2F6. Since the second step consumes B2F6, and the first step produces B2F6, the availability of B2F6 will determine the rate of the reaction. Therefore, the second step is the limiting step.
c. To determine the rate law for the overall reaction, we need to examine the slowest step, which is the limiting step. The rate law is determined by the reactants involved in the limiting step. In this case, the second step is the limiting step, and it involves the reactants B2F6 and NH3. The rate law for this step can be written as:
Rate = k [B2F6] [NH3]
d. The intermediate compound in this reaction is F3BNH3. An intermediate is a compound that is formed in one step of the reaction but consumed in a subsequent step. In this mechanism, F3BNH3 is formed in the second step, but then reacted further in the subsequent step, making it an intermediate compound.