Syllabus Edition
First teaching 2023
First exams 2025
Why does a mixture of hydrogen gas and bromine gas react together faster at a temperature of 500 K than it does at a temperature of 400 K?
| 1 |
A higher proportion of effective collisions occurs at 500 K. |
| 2 |
Hydrogen molecules and bromine molecules collide more frequently at 500 K. |
| 3 |
The activation energy of the reaction is lower at 500 K. |
1 only
1 and 2
3 only
1, 2 and 3
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What is the main reason for the increase in reaction rate with increasing temperature?
The activation energy decreases.
The activation energy increases.
The molecules collide more frequently.
More molecules have an energy greater than the activation energy.
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A student measured the rate of a reaction at two different temperatures: 40 °C and 50 °C. They observed that the rate of reaction roughly doubled.
What explains this observation?
Raising the temperature by 10 °C doubles the average velocity of the molecules.
Raising the temperature by 10 °C doubles the average kinetic energy of each molecule.
Raising the temperature by 10 °C doubles the number of molecules having more than a certain minimum energy.
Raising the temperature by 10 °C doubles the number of molecular collisions in a given time.
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When the pressure of a fixed mass of gaseous reactants is raised at a constant temperature, the rate of reaction increases.
Which of the following statements explain this observation?
|
1 |
Raising the pressure lowers the activation energy. |
|
2 |
More molecules have energy greater than the activation energy at the higher pressure. |
|
3 |
More collisions occur per second when the pressure is increased. |
1 only
1 and 2
3 only
1, 2 and 3
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When 1 cm3 of 0.1 mol dm–3 HCl is added to 10 cm3 of 0.02 mol dm–3 Na2S2O3 pale yellow precipitate forms slowly.
When the experiment is repeated with 1 cm3 of 0.1 mol dm–3 HCl and 10 cm3 of 0.05 mol dm–3 Na2S2O3 the precipitate forms more quickly.
Why is this?
When 0.05 mol dm–3 Na2S2O3 is used the reactant particles collide more frequently.
When 0.05 mol dm–3 Na2S2O3 is used the collisions between reactant particles are more violent.
When 0.05 mol dm–3 Na2S2O3 is used the activation energy of the reaction is lower.
When 0.05 mol dm–3 Na2S2O3 is used the reaction proceeds by a different pathway.
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A quantity of solid Y was placed in a previously evacuated vessel, and the apparatus was then held at a series of different temperatures. At each temperature, the mass of Y in the vapour state was calculated from pressure measurements. The results are shown below.
What can be deduced from the diagram?
| 1 |
The mass of Y used in the experiment was m. |
| 2 |
The pressure of the vapour was constant for all temperatures above temperature T. |
| 3 |
Liquid appeared at temperature T. |
1 only
1 and 3
2 and 3
1, 2 and 3
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On the graph, curve 1 was produced from measuring the decomposition of 100 cm3 of 1.0 mol dm–3 hydrogen peroxide in the presence of a manganese (IV) oxide catalyst.
Which alteration to the original experimental conditions would produce curve 2?
Raising the temperature.
Adding more manganese (IV) oxide.
Adding water.
Adding some 0.1 mol dm–3 hydrogen peroxide.
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A student performs to reactions and measures the rate of product formation.
Reaction 1: 1.5 g of solid calcium carbonate is added to 100 cm3 of 0.5 M hydrochloric acid.
Reaction 2: 100 cm3 of distilled water is then added to 100 cm3 of 0.5 M hydrochloric acid then 1.5 g of solid calcium carbonate is added.
The rate of reaction 1 was faster than the rate of reaction 2.
Which of the following 3 hypotheses correctly describes the difference in the rate?
|
1 |
Adding water reduces the frequency of collisions between reactant molecules. |
|
2 |
Adding water reduces the proportion of effective collisions between reactant molecules. |
|
3 |
Adding water reduces the proportion of reactant molecules possessing the activation energy. |
1 only
1 and 2
3 only
1, 2 and 3
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A student performs two reactions and measures the rate of product formation.
The rate of reaction 1 was faster than the rate of reaction 2.
Which of the following 3 hypotheses correctly describes the difference in the rate as a result of adding water?
| Frequency of collisions between reactant molecules is reduced | Proportion of effective collisions between reactant molecules is reduced | Proportion of reactant molecules possessing the activation energy is reduced | |
| A | X | X | ✓ |
| B | ✓ | ✓ | X |
| C | ✓ | X | X |
| D | ✓ | ✓ | ✓ |
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Consider the following reaction:
NaOH (aq) + HCl (aq) → H2O (l) + NaCl (aq)
Which species could a student change the concentration of, in order to determine the rate of reaction?
H+
Cl-
Na+
H2O
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