Syllabus Edition
First teaching 2014
Last exams 2024
Which of the following factors can affect the value of the activation energy of a reaction?
|
1 |
the presence of a catalyst |
|
2 |
changes in temperature |
|
3 |
changes in the concentration of the reactants |
1 only
1 and 2 only
3 only
1, 2 and 3
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The oxidation of butadiene, CH2=CHCH=CH2, using air or oxygen, produces the molecule crotonaldehyde, CH3CH=CHCHO.
One method of oxidation is to pass a mixture of butadiene and oxygen through a hot aqueous solution of palladium(II) ions, Pd2+(aq), which catalyse the reaction.
Which statement about the action of the Pd2+(aq) ions is not correct?
Pd2+(aq) lowers the activation energy for the reaction
Pd2+(aq) increases the energy of the reacting molecules
When Pd2+(aq) is used, the reaction proceeds by a different route
Changing the concentration of the Pd2+(aq) affects the rate of oxidation
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The Maxwell-Boltzmann energy distribution curve below describes a mixture of two gases at a given temperature. For a reaction to occur between the gaseous molecules, they must collide with sufficient energy.
Of the two activation energy (Ea) values shown, one is for a catalysed reaction, the other for an uncatalysed one.
When a catalyst is used, which pair of statements is correct?
|
A B C D |
Ea1 uncatalysed reaction fewer effective collisions Ea1 catalysed reaction fewer effective collisions Ea1 uncatalysed reaction more effective collisions Ea1 catalysed reaction more effective collisions |
Ea2 catalysed reaction more effective collisions Ea2 uncatalysed reaction more effective collisions Ea2 catalysed reaction fewer effective collisions Ea2 uncatalysed reaction fewer effective collisions |
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Ammonia is manufactured using the Haber process, which is represented by the following equation:
N2 (g) + 3H2 (g) format('truetype')%3Bfont-weight%3Anormal%3Bfont-style%3Anormal%3B%7D%3C%2Fstyle%3E%3C%2Fdefs%3E%3Ctext%20font-family%3D%22math1aa495e18c7e3a21a4e48923b92%22%20font-size%3D%2216%22%20text-anchor%3D%22middle%22%20x%3D%2210.5%22%20y%3D%2216%22%3E%26%23x21CC%3B%3C%2Ftext%3E%3C%2Fsvg%3E)
2NH3 (g) ∆H = –93 kJ mol–1
What happens to the rate of the forward and backward reactions when the temperature is increased?
there is no effect on the backward or forward rate
both forward and backward rates increase
the forward rate only increases
the backward rate only increases
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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 only
3 only
1, 2 and 3
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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 only
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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The diagram represents the reaction pathway for the following reaction:
Z(g) + Y(g) → X(g) + W(g)
What statement is true about the reverse reaction, W(g) + X(g) → Y(g) + Z(g)?
it will have a smaller activation energy and a negative ∆H
it will have a smaller activation energy and a positive ∆H
it will have a larger activation energy and a negative ∆H
it will have a larger activation energy and a positive ∆H
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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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Which statements correctly describe how a catalyst works?
|
1 |
a catalyst has no effect on the enthalpy change of the reaction |
|
2 |
a catalyst increases the rate of the reverse reaction |
|
3 |
a catalyst increases the average kinetic energy of the reacting particles |
1 only
1 and 2 only
3 only
1, 2 and 3
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The distribution of molecular energies in a sample of a gas at a given temperature is shown by the Boltzmann distribution graph below.
If the temperature is increased, what will happen to the position of point X?
fewer molecules possess the most probable energy value so X will shift to the right
fewer molecules possess the most probable energy value so X will shift to the left
more molecules possess the most probable energy value so X will shift to the left
the position of X will stay the same but the area under the distribution curve increases
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The diagram shows a reaction pathway for an endothermic reaction.
Which arrow represents the activation energy for the forward reaction?
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The dotted-line curve on each graph below represents the corresponding distribution for a gas at 300 K.
Which solid-line curve most accurately represents the distribution of molecular energies in the same gas at 500 K?
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The energies of the reactants, the products and the transition state of a reaction are shown in the reaction pathway diagram below.
Which expression correctly represents how to calculate the activation energy of the forward reaction?
E1 – E2
E2 – E1
E2 – E3
E3 – E2
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The diagram below represents, for a given temperature, the Boltzmann distribution of the kinetic energy of the molecules in a mixture of two gases that react slowly together without a catalyst.
The activation energy for the reaction, Ea, is marked for the uncatalysed reaction
What would the position of Ea be if the reaction took place with an effective catalyst?
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Four possible energy profiles are shown below, for reactions carried out at the same temperature.
Which energy profile shows a reaction that is likely to proceed most rapidly and with a good yield?
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The diagram shows a Boltzmann distribution of molecular energies for a gaseous mixture. The distribution has a peak, labelled Q on the diagram.
What happens when an effective catalyst is added to the mixture?
the height of the peak remains the same, and the activation energy moves to the left
the height of the peak decreases and the activation energy moves to the left
the height of the peak remains the same, and the activation energy moves to the right
the height of the peak decreases and the activation energy moves to the right
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A student performs two reactions and measures the rate of product formation.
Reaction 1: 1.5g 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 1.5g 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 only
3 only
1, 2 and 3
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The Boltzmann distribution shows the number of molecules that have particular kinetic energy at a constant temperature.
If the temperature is decreased by 10 format('truetype')%3Bfont-weight%3Anormal%3Bfont-style%3Anormal%3B%7D%3C%2Fstyle%3E%3C%2Fdefs%3E%3Ctext%20font-family%3D%22math138af86134b65d0f10fe33d30dd%22%20font-size%3D%2216%22%20text-anchor%3D%22middle%22%20x%3D%224.5%22%20y%3D%2216%22%3E%26%23xB0%3B%3C%2Ftext%3E%3C%2Fsvg%3E)
C, what happens to the size of the areas labelled H, J and K?
|
|
H |
J |
K |
|
A B C D |
decreases decreases increases increases |
decreases increases decreases decreases |
decreases decreases decreases increases |
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Zinc reacts with copper sulfate according to the following equation:
Zn (s) + CuSO4 (aq) → Cu (s) + ZnSO4 (aq)
Rates of reaction can be found by measuring how certain properties change during the course of the reaction. Which of these properties could be used?
| 1 |
Change in volume |
| 2 |
Change in temperature |
| 3 |
Change in colour |
1 and 2 only
1 and 3 only
2 and 3 only
1, 2 and 3
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In a reaction between 1M hydrochloric acid and an excess of marble chips (calcium carbonate) the volume of gas produced was measured against time. This is shown on the dotted line in the graph below.
The experiment was repeated, but this time using the same volume of 2M hydrochloric acid. Which line on the graph represents this experiment?
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1 dm3 of gas X and 1 dm3 of gas Y are kept at the same temperature and pressure.
The speed of the molecules is plotted against the fraction of molecules with that speed. From the graph what can be said about the two gases?
The molar mass of X is larger than the molar mass of Y
The molar mass of Y is larger than the molar mass of X
The average kinetic energy of X is higher than that of Y
The average kinetic energy of Y is higher than that of X
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A beaker containing 100 cm3 of 2M sulfuric acid, H2SO4 (aq), was placed on a balance and then an excess of powdered zinc was added. The change in mass was recorded against time and the results plotted on a graph as shown in line I below.
What change in conditions could result in line II shown on the graph?
Using twice as much powdered Zn
Using pieces of zinc that have the same mass as the powder
Raising the temperature of the sulfuric acid, H2SO4 (aq)
Using more concentrated H2SO4 (aq), but keeping the volume the same
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Bleach solution contains sodium chlorate (I) which naturally decomposes according to the equation below:
2NaClO (aq) → 2NaCl (aq) + O2 (g)
The bleach decomposes faster as the temperature increases. A 100 cm3 sample of 10% bleach was heated to 40 C and the amount of oxygen evolved was measured against time.
The experiment was repeated under the same conditions, but this time using a 100 cm3 sample of 20% bleach. If the first experiment produces the dotted line, which line is produced by the second experiment?
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How does the average kinetic energy of a gas vary with temperature?
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Three batches of sulfuric acid containing different volumes and concentrations were reacted with an excess of zinc powder. The hydrogen evolved was measured against time and the results were plotted on a graph. Which lines on the graph could correspond to the specified volumes and concentrations of the sulfuric acid shown in the table?
|
|
25 cm3 of 1.0 M H2SO4 |
50 cm3 of 0.5 M H2SO4 |
25 cm3 of 0.5 M H2SO4 |
|
A |
I |
III |
IV |
|
B |
I |
IV |
III |
|
C |
I |
II |
III |
|
D |
II |
I |
III |
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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 solution, a 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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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
using more concentrated hydrogen peroxide
add some 0.1 mol dm–3 hydrogen peroxide
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The stoichiometry of a catalysed reaction is shown by the equation below.
R (g) + S (g) ⇌ T (g) + U (g)
Two experiments were carried out in which the amount of product T was measured against time. The results are shown in the diagram below.
Which changes in the conditions from experiment 1 to experiment 2 might explain the results shown?
|
1 |
product U was continuously removed from the equilibrium mixture |
|
2 |
a different catalyst was used |
|
3 |
less of reactant R was used |
1 only
1 and 3 only
2 and 3 only
1, 2 and 3
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Boltzmann distributions are shown in the two diagrams below.
In diagram 1, one line, P or Q, corresponds to the activation energy in the presence of a catalyst and the other line corresponds to the activation energy of the same reaction in the absence of a catalyst.
In diagram 2, one curve, X or Y, corresponds to a temperature higher than that of the other curve.
Which combination gives the correct curve and line?
|
|
presence of catalyst |
higher temperature |
|
A B C D |
P P Q Q |
X Y X Y |
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