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:
To determine which statement is false, let's analyze each statement based on the given mechanism.
a. The reaction is first order with respect to H2O2.
In the first step, the rate-determining step (slow step), H2O2 reacts with I- to produce H2O and IO-. Since the reaction rate depends on the concentration of H2O2 alone in this step, it is indeed first order with respect to H2O2. This statement is correct.
b. The reaction is first order with respect to I-.
In the first step, H2O2 reacts with I- to produce H2O and IO-. In this step, the rate depends on the concentration of I- as well. However, in the second step (fast step), H2O2 reacts with IO- to produce H2O, O2, and I-. Since the second step involves the consumption of IO-, the rate is affected by the concentration of IO- as well. Thus, the overall reaction rate depends on both H2O2 and IO-, making the statement false.
c. I- is a catalyst.
A catalyst is a substance that participates in a reaction but is not consumed. In the given mechanism, I- appears in both the slow and the fast step. Since it is consumed in the second step, it cannot be considered a catalyst. Hence, the statement is false.
d. IO- is an intermediate.
An intermediate is a species that is formed and consumed during the reaction but does not appear in the final products. In the given mechanism, IO- is formed in the first step as a product but is consumed in the second step. It does not appear in the final products (H2O and O2). Hence, IO- is indeed an intermediate. This statement is correct.
Based on this analysis, the false statement is b. The reaction is not first order with respect to I-.
Therefore, the answer is b.
For question 2:
The given reaction is A + 2B = C + D, which is an elementary reaction taking place in a single step. The stoichiometric coefficient of A is 1, and the stoichiometric coefficient of B is 2. The rate law for an elementary reaction is determined by the stoichiometric coefficients of the reactants.
The rate law is given by the exponents of the concentrations of the reactants raised to their respective stoichiometric coefficients. In this case, the rate law will be:
rate = k(A)(B)^2
Hence, the correct answer is a. rate = k(A)(B)^2.
Therefore, your answer for the second question is correct.