Exam code: 7404
Which of the following factors can affect the value of the activation energy of a reaction?
| The presence of a catalyst | Changes in temperature | Changes in the concentration of the reactants |
A | ✓ | ⨯ | ⨯ |
B | ✓ | ✓ | ⨯ |
C | ⨯ | ⨯ | ✓ |
D | ✓ | ⨯ | ✓ |
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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
When Pd2+ (aq) is used, the reaction proceeds by a different route
Pd2+ (aq) increases the energy of the reacting molecules
Changing the concentration of the Pd2+ (aq) affects the rate of oxidation
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Why does a mixture of hydrogen gas and chlorine gas react faster at a temperature of 600 K than at 500 K?
| A higher proportion of successful collisions occurs at 600 K | Hydrogen molecules and chlorine molecules collide more frequently at 600 K | The activation energy of the reaction is lower at 600 K |
A | ✓ | ⨯ | ⨯ |
B | ✓ | ✓ | ⨯ |
C | ⨯ | ⨯ | ✓ |
D | ✓ | ✓ | ✓ |
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What is the main reason for reaction rate increasing as temperature increases?
The activation energy decreases
The activation energy increases
More molecules have an energy ≥ the activation energy
The molecules collide more frequently
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This energy profile diagram represents the reaction pathway for the following reaction:
Y (g) + Z (g) → W (g) + X (g)
Which statement is true about the reverse reaction, W(g) + X(g) → Y(g) + Z(g)?
It will have a negative ΔH
It will have a positive ΔH
It will have a smaller activation energy
The temperature of the surroundings increase
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This question concerns the Maxwell-Boltzmann energy distribution shown below.
How does the curve change when the temperature is increased?
Stays the same
Peak height decreases and moves to the left
Peak height increases and moves to the right
Peak height decreases and moves to the right
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The Maxwell–Boltzmann distribution for a sample of a gas, Z, at two different temperatures, T1 and T2, is shown.
Which letter represents the mean energy of molecules at a higher temperature?
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The Maxwell-Boltzman distribution of molecular energies in a sample of gas is shown.
What does the area underneath the curve represent?
The number of particles which can react with each other
The total number of particles
The total energy of the particles
The total number of particles that have activation energy
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The Maxwell-Boltzman distribution of molecular energies in a sample of gas is shown.
What effect would adding a catalyst have on the activation energy, Ea?
Move to the left and the peak would be unchanged
Move to the left and the peak would move to the right
Move to the left and the peak would move to the left
The activation energy would be unchanged and the peak move to the right
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The Maxwell-Boltzman distribution of molecular energies in a sample of gas is shown.
What does the shaded area represent?
The total number of particles that do have enough energy to react
The total number of particles that do not have enough energy to react
The total number of particles that do have enough energy to react in the presence of a catalyst
The total number of particles that do not have enough energy to react in the presence of a catalyst
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The Maxwell-Boltzmann distribution of molecular energies in a sample of a gas at a given temperature is shown.
If the temperature is increased, what will happen to the position of point X?
X will shift up and to the left showing that fewer molecules possess the most probable energy
X will shift down and to the right showing that fewer molecules possess the most probable energy
X will shift left showing that more molecules possess the most probable energy
X will remain the same but the area under the distribution curve increases
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The reaction pathway for an endothermic reaction is shown.
Which arrow represents the activation energy for the reverse reaction?
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The dotted-line curve on each graph below represents the corresponding Maxwell-Boltzmann distribution for a gas at 200 K.
Which solid-line curve most accurately represents the Maxwell-Boltzmann distribution of molecular energies in the same gas at 400 K?
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The reaction pathway shows the energies of the reactants, the products and the transition state of a reaction.
Which expression correctly represents how to calculate the activation energy of the forward reaction?
E3 – E2
E2 – E1
E2 – E3
E1 – E2
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The Maxwell-Boltzmann distribution of the kinetic energies of molecules in a slowly reacting gaseous mixture, without a catalyst, at a given temperature is shown.
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 reactions (A, B, C and D) of the following equation are measured at the same temperature.
X (g) + Y (g) → Z (g)
Which reaction pathway diagram shows the reaction occurring rapidly with an overall negative enthalpy value?
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The diagram shows a Maxwell-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 right
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 left
the height of the peak decreases and the activation energy moves to the right
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The Maxwell-Boltzmann distribution of the distribution of molecular energies in sample 1 of a gas is shown.
A change was made to the reaction conditions, as shown by the dotted curve, labelled sample 2.
What factor was changed in the reaction conditions to produce the dotted curve, labelled sample 2?
| Temperature increased | Catalyst added | Concentration reduced |
A | ⨯ | ⨯ | ✓ |
B | ⨯ | ⨯ | ⨯ |
C | ✓ | ⨯ | ⨯ |
D | ⨯ | ✓ | ⨯ |
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A student performs two 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 mol dm-3 hydrochloric acid.
Reaction 2: 100 cm3 of distilled water is added to 100 cm3 of 0.5 mol dm-3 hydrochloric acid and 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 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 | ⨯ | ⨯ | ✓ |
B | ✓ | ✓ | ⨯ |
C | ✓ | ⨯ | ⨯ |
D | ✓ | ✓ | ✓ |
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The Maxwell-Boltzmann distribution shows the number of molecules that have particular kinetic energy at a constant temperature.
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C, what happens to the size of the areas labelled H, J and K?
| H | J | K |
A | decreases | increases | decreases |
B | decreases | decreases | decreases |
C | increases | decreases | increases |
D | increases | decreases | decreases |
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In a sealed container, a mixture of gases reacted together at 300 K. The temperature was then increased to 400 K as shown on the Maxwell-Boltzmann distribution curve.
Which of the following statements are correct about the reaction at 400 K?
| All reacting molecules have greater kinetic energy | The most probable energy value, Emp will be higher | The area under the curve has increased | More particles have energy ≥ Ea |
A | ✓ | ✓ | ✓ | ⨯ |
B | ✓ | ⨯ | ⨯ | ✓ |
C | ⨯ | ⨯ | ⨯ | ✓ |
D | ⨯ | ✓ | ⨯ | ✓ |
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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?
Increase the temperature
Add 0.1 mol dm–3 hydrogen peroxide
Add water
Add more manganese (IV) oxide
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In a reaction between 1.00 mol dm-3 hydrochloric acid and an excess of calcium carbonate chips, 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 2.00 mol dm-3 hydrochloric acid.
Which line on the graph represents this experiment?
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The diagrams below shows the Maxwell–Boltzmann distribution of molecular energies in a sample of gas.
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 | P | X |
B | P | Y |
C | Q | X |
D | Q | Y |
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In an experiment 1.0 mol dm-3 H2O2 was reacted with hydrochloric acid at 20 C and the volume of oxygen recorded, as shown by curve 1.
The experiment was repeated a second time to produce curve 2.
What factor was changed to produce curve 2?
The temperature was raised to 30 C
A catalyst was used
0.5 mol dm-3 H2O2 used
The temperature was lowered to 10 C
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Hydrogen will react with chlorine to form hydrogen chloride gas.
Apart from increasing temperature, what other two factors could speed up the rate of hydrogen chloride formation?
| Heterogeneous catalyst | Increase the most probable energy, Emp | Increase pressure | Decrease pressure |
A | ✓ | ⨯ | ✓ | ⨯ |
B | ✓ | ⨯ | ⨯ | ✓ |
C | ⨯ | ⨯ | ⨯ | ✓ |
D | ⨯ | ✓ | ✓ | ⨯ |
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Which arrow indicates the activation energy for a catalysed reaction on the reaction profile shown?
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Consider the Maxwell-Boltzmann distribution curve below.
What would be the effect on the distribution curve if the number of molecules in the original reaction mixture is increased, but no other changes are made?
| Area under the curve increases | Most probable energy, Emp increases | Number of molecules with energy ≥ Ea increases | Curve shifts upwards and to the left |
A | ⨯ | ✓ | ✓ | ⨯ |
B | ✓ | ⨯ | ⨯ | ✓ |
C | ✓ | ⨯ | ✓ | ⨯ |
D | ⨯ | ⨯ | ✓ | ⨯ |
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Consider the Maxwell-Boltzmann distribution of molecular energies for gaseous molecules, with and without a catalyst.
What would always result in a decrease in the number of molecules contained within area Y?
| Decrease pressure | Decrease temperature | Putting the gas into a smaller container | Removing a quarter of the catalyst |
A | ⨯ | ⨯ | ✓ | ⨯ |
B | ⨯ | ✓ | ⨯ | ⨯ |
C | ⨯ | ✓ | ⨯ | ✓ |
D | ✓ | ✓ | ⨯ | ⨯ |
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30.0 cm3 of 0.750 mol dm−3 aqueous ethanoic acid reacts with 390 mg sodium which is the limiting reagent.
Hydrogen gas is produced and collected with a gas syringe.
What is the minimum mass, in mg, of sodium required to react?
259
5.18 x 10-1
518
9.78 x 10-4
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