1)Thallium (I) is oxidized by cerium (IV) as follows: Tl+ + 2 Ce+4 Tl+3 + 2 Ce+3
The elementary steps, in the presence of Mn(II), are as follows:
Step 1 Ce+4 + Mn+2 --- Ce+3 + Mn+
Step 2 Ce+4 + Mn+3 ---- Ce+3 + Mn+4 Step 3 Tl+ + Mn+4 ----- Tl+3 + Mn+2
(a) Identify the catalyst, intermediates, and the rate determining step if the rate law is r = k[Ce+4[Mn+2].
(b) Explain why the reaction is slow without a catalyst.
Iron (III)
(a)catalyst Mn2+
intermediates Mn3+,Mn+, Mn4+
RDS Step 2
(b)require high activation energy for reaction to occur
(a) In the given reaction, the catalyst is Mn(II).
Intermediates:
- Ce+3: Formed in step 1 and consumed in step 2.
- Mn+: Produced in step 1 and consumed in step 3.
- Mn+4: Produced in step 2 and consumed in step 1.
Rate determining step:
The rate determining step is step 2 since the reaction rate depends on the concentration of both Ce+4 and Mn+2.
(b) The reaction is slow without a catalyst because the activation energy for the reaction is high. The presence of a catalyst, in this case, Mn(II), provides an alternative reaction pathway with a lower activation energy, allowing the reaction to proceed at a faster rate. The catalyst allows the reaction to occur by providing an alternate reaction pathway with a lower activation energy, which accelerates the reaction by lowering the energy barrier.
(a) In order to identify the catalyst, intermediates, and the rate-determining step, we need to examine the elementary steps given and the rate law provided.
From the elementary steps:
Step 1: Ce+4 + Mn+2 --- Ce+3 + Mn+
Step 2: Ce+4 + Mn+3 ---- Ce+3 + Mn+4
Step 3: Tl+ + Mn+4 ----- Tl+3 + Mn+2
The rate law is given as r = k[Ce+4][Mn+2], which means that the rate of the overall reaction depends on the concentrations of Ce+4 and Mn+2.
Since the rate law does not include Tl+, we can conclude that Tl+ is not involved in the rate-determining step and is therefore an intermediate.
From the elementary steps, we can see that Ce+4 is present in both Step 1 and Step 2, and Mn+2 is present in both Step 1 and Step 3. Thus, Ce+4 and Mn+2 are both catalysts.
The rate-determining step is the slowest step in the reaction mechanism, and it usually involves the species present in the rate law. In this case, the rate-determining step involves Ce+4 and Mn+2 in Step 1 (Ce+4 + Mn+2 --- Ce+3 + Mn+). Therefore, Step 1 is the rate-determining step.
(b) The reaction is slow without a catalyst because the presence of a catalyst provides an alternative reaction pathway with lower activation energy. In the absence of a catalyst, the reactants need to overcome a higher energy barrier to form products. This requires more energy to initiate the reaction, making it slower.
A catalyst works by providing an alternative mechanism that allows the reaction to proceed faster by lowering the activation energy. It does not get consumed in the reaction and can be reused. In this reaction, Ce+4 and Mn+2 act as catalysts to facilitate the oxidation of Thallium (I) by cerium (IV).