Rate-determining step & mechanisms

This question is about equilibrium and rates.

This question is about elements in the periodic table.

Chlorine has many uses.

Chlorine is used to treat water in large-scale water treatment plants.

Suggest why chlorine is added to water in large-scale water treatment plants.

Sea water contains aqueous bromide ions.

Chlorine is used to extract bromine from sea water.

Construct the ionic equation for this reaction and explain why chlorine is suitable for this extraction of bromine but iodine is not.

Equation........

Explanation........

Fluorine, F₂, reacts with nitrogen dioxide, NO₂, to form nitryl fluoride, NO₂F, as shown in Reaction 20.1 below.

The mechanism for this reaction involves two steps. Step 1 is the ‘slow’ step and Step 2 is the ‘fast’ step.

The equation for Step 2 is shown below:

Suggest the equation for Step 1 and the rate equation for Reaction 20.1.

Equation for Step 1:........

Rate equation for Reaction 20.1:........

* The table shows the melting points of some of the elements in Period 3 of the periodic table.

Element	Al	Si	P4	S8
Melting point / C	660	1410	44	119

Explain the melting points in terms of bonding and structure.

A catalytic converter in a car removes nitrogen monoxide, NO, and carbon monoxide, CO, from the exhaust gases.

One reaction that happens in a catalytic converter is shown below.

Explain how increasing the temperature increases the rate of Reaction 16.1.

Include a labelled sketch, using Boltzmann distributions, on the grid below.

Label the axes.

Carbon monoxide also reacts with nitrogen dioxide as shown in Reaction 16.2.

The rate equation for Reaction 16.2 is shown below:

rate = k [NO₂(g)]²

Suggest a possible two-step mechanism for Reaction 16.2. The first step is much slower than the second step.

This question is about how the rate of reaction is affected by changes in conditions.

A student carries out two investigations using the reaction between aqueous thiosulfate ions, S₂O₃^2–(aq), and aqueous hydrogen ions, H⁺(aq). Reaction 21.1 S₂O₃^2–(aq) + 2H⁺(aq) → S(s) + SO₂(g) + H₂O(l)

Explain how the student’s results support this rate equation.

Predict a possible two-step mechanism for Reaction 21.1. The first step is the rate-determining step.

Step 1........

Step 2........

Calculate the activation energy, E_a, for Reaction 21.1, in kJ mol^–1.

Give your answer to 3 significant figures.

E_a =........ kJ mol^–1

From the graph the student estimates the value of ln A as –2.00. (A is the pre-exponential factor.)

Explain what mistake the student has made.

* Determine the rate constant and a possible two-step mechanism for this reaction that are

consistent with these results.

A student carries out an investigation to find the activation energy, E_a, and the pre-exponential factor, A, of a reaction.

The student determines the rate constant, k, at different temperatures, T. The student then plots a graph of ln k against 1 / T as shown below.

Draw a best-fit straight line and calculate the activation energy, in J mol^–1. Give your answer to three significant figures.

Show your working.

activation energy, E_a = +........ J mol^–1

Use the graph to calculate the value of the pre-exponential factor, A.

Show your working.