The Maxwell‐Boltzmann distribution of molecular energies for the reactant molecules in an uncatalysed reaction is shown.
Which of these Maxwell‐Boltzmann distributions would you expect for the same molecules in the presence of a catalyst at the same temperature and pressure?
All diagrams are drawn to the same scale.
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This question is about reaction kinetics.
The best way to describe the activation energy of a reaction is
| ☐ | A | the average energy of the particles when they react | |
| ☐ | B | the difference in energy between the reactants and the products | |
| ☐ | C | the minimum energy required to make the particles collide | |
| ☐ | D | the minimum energy required for a reaction to occur |
2 marksThe diagrams show two reaction profiles for the same reversible reaction involving gaseous reactants.
Shown on each diagram are the reaction profiles for the pathway without a catalyst and the pathway catalysed by a heterogeneous catalyst.
(1)
| ☐ | A | 75 kJ mol−1 | |
| ☐ | B | 100 kJ mol−1 | |
| ☐ | C | 175 kJ mol−1 | |
| ☐ | D | 200 kJ mol−1 |
State why a solid (heterogeneous) catalyst is suitable for a reaction in the gas phase.
The diagram shows a Maxwell‐Boltzmann distribution of molecular energies for gaseous molecules.
| ☐ | A | Y | |
| ☐ | B | Y - Z | |
| ☐ | C | Y + Z | |
| ☐ | D | Z |
| ☐ | A | decreasing the temperature of the gas | |
| ☐ | B | increasing the pressure of the gas | |
| ☐ | C | putting the gas in a smaller container | |
| ☐ | D | removing a quarter of the catalyst |
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A series of experiments was carried out to investigate the factors which affect the rate of reaction between calcium carbonate and dilute hydrochloric acid.
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)
| Experiment | Size of calcium carbonate | Concentration of hydrochloric acid / mol dm−3 | Temperature /°C |
| 1 | small pieces | 0.50 | 20 |
| 2 | small pieces | 0.50 | 60 |
| 3 | one large piece | 0.50 | 20 |
| 4 | small pieces | 1.00 | 20 |
The results of Experiment 1 are shown on the graph.
Draw curves on the graph to show the results you would expect for
Experiments 2, 3 and 4. Label the curves 2, 3 and 4.
3 marksDetermine the initial rate of reaction for Experiment 1.
You must show your working on the graph.
Include units in your answer.
Initial rate of reaction .........................................................
A student was required to devise an alternative method of carrying out this experiment that involved collecting the gas produced.
Outline the procedure that the student could use, including a diagram and the measurements needed.
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Aqueous hydrogen peroxide decomposes according to the following equation.
2H2O2 (aq) → 2H2O (l) + O2 (g)
The decomposition is catalysed by manganese(IV) oxide.
This can be investigated by measuring the volume of oxygen produced at various times as the reaction proceeds. Part of the apparatus used in the experiment is shown.
The manganese(IV) oxide is placed in a small glass container, which is then tipped over to start the reaction. A stop clock is started at the same time.
Complete the diagram to show how the gas can be collected and its volume measured, labelling the apparatus used.
7 marksAn experiment was carried out using 0.25 g of manganese(IV) oxide granules and 50 cm3 of aqueous hydrogen peroxide of concentration 0.16 mol dm−3. The results are shown in the table and plotted on a graph.
| Time/s | 0.0 | 20.0 | 30.0 | 50.0 | 60.0 | 80.0 | 100 | 120 | 150 |
| Volume of O2 / cm3 | 0 | 51 | 68 | 85 | 88 | 91 | 92 | 92 | 92 |
(1)
(2)
(2)
Catalysts are not used up during a reaction. Manganese(IV) oxide acts as a heterogeneous catalyst.
Describe in outline a method to show that the manganese(IV) oxide is not used up in the decomposition of hydrogen peroxide and that it still functions as a catalyst.
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Compound X reacts slowly with water according to the following equation.
X(s) + H2O(l) → Y(aq) + Z–(aq) + H+(aq)
The reaction is catalysed by hydrogen ions and eventually goes to completion.
Compound X was added to water and the concentration of compound Y determined at various times at a constant temperature.
The results of the experiment are shown.
| Time / s | Concentration of Y / mol dm–3 |
| 0 | 0.000 |
| 25 | 0.002 |
| 40 | 0.005 |
| 50 | 0.010 |
| 65 | 0.020 |
| 75 | 0.030 |
| 85 | 0.040 |
| 100 | 0.050 |
| 115 | 0.060 |
| 140 | 0.070 |
| 200 | 0.080 |
| 260 | 0.085 |
| 380 | 0.090 |
Complete the graph of concentration against time by adding the six missing points.
Draw a line to pass through all the points.
(2)
(4)
For many reactions, the values of the initial rate and the maximum rate are the same.
Explain why the values of the two reaction rates obtained in this experiment are different from each other.
Give a reason why the measurement of the initial rate of reaction is likely to be less accurate than the measurement of the maximum rate.
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