1) The decomposition of hydrogen peroxide in solution and in the presence of iodide ion was studied in laboratory, and the following mechanism proposed based on the experimental data.
H2O2 + I - = H2O + IO - (slow)
H2O2 + IO - = H2O + O2 + I - (fast)
Which one of the following statements is false? Choose answer (E) if more than one or none are false.
a. The reaction is first order with respect to H2O2.
b. The reaction is first order with respect to I -
c. I - is a catalyst.
d. IO - is an intermediate.
e. More than one the above statements is false (or none of the statements are false).
I chose that more than one of the statements are correct because I think that statements 1 and 2 regarding the order are correct.
2) The equation A + 2 B = C + D describes an elementary reaction, which takes place in a single step. Thus, the rate law must be
a. rate = k(A)2
b. rate = k(B)2
c. rate = k(A)(B)
d. rate = k(A)(B)2
e. none of the above represents the rate law for this elementary reaction.
I am not sure about this one. I think that the answer is either k(A)(B)^2 or none of these.
Are these correct?
For question 1, let's go through each statement to determine if it is true or false:
a. The reaction is first order with respect to H2O2.
To determine the reaction order with respect to H2O2, we need to look at the rate-determining step, which is the slow step in the mechanism. In this case, the slow step is H2O2 + I- = H2O + IO-. Since the rate of the reaction is dependent on the concentration of H2O2 in the slow step, we can conclude that statement (a) is true.
b. The reaction is first order with respect to I-.
Similarly, for the reaction order with respect to I-, we look at the slow step. Since the rate of the reaction is dependent on the concentration of I- in the slow step, we can conclude that statement (b) is true as well.
c. I- is a catalyst.
A catalyst is a substance that participates in the reaction but is not consumed during the reaction. In this mechanism, I- is consumed in the slow step and regenerated in the fast step. Therefore, statement (c) is false.
d. IO- is an intermediate.
An intermediate is a species that is formed in one step of the reaction and consumed in a subsequent step. In this mechanism, IO- is formed in the first step and consumed in the second step. Therefore, statement (d) is true.
e. More than one of the above statements is false (or none of the statements are false).
Since statement (c) is false while statements (a), (b), and (d) are true, the answer is (e) - more than one of the above statements is false.
For question 2, let's go through each option:
a. rate = k(A)2
This represents a second-order reaction, where the rate is proportional to the square of the concentration of A. Therefore, option (a) is incorrect.
b. rate = k(B)2
Similarly, this also represents a second-order reaction, but with respect to B. Therefore, option (b) is incorrect.
c. rate = k(A)(B)
This represents a first-order reaction with respect to both A and B. However, the coefficient of B in the balanced chemical equation is 2, indicating that B is consumed twice as fast as A. Therefore, option (c) is incorrect.
d. rate = k(A)(B)2
This represents a first-order reaction with respect to A and a second-order reaction with respect to B. However, the balanced equation does not support this reaction order, as the coefficient of B is 2, not squared. Therefore, option (d) is incorrect.
e. none of the above represents the rate law for this elementary reaction.
Based on the analysis above, we can conclude that none of the given options accurately represents the rate law for this elementary reaction. Therefore, option (e) is correct.
In summary, for question 1, the correct answer is (e) more than one of the above statements is false. For question 2, the correct answer is (e) none of the above represents the rate law for this elementary reaction.