Rates of Reaction and EquilibriumIB MYP Chemistry: Topic test

20 questions, 54 marks

IB MYP Chemistry

Rates of Reaction and Equilibrium topic test

Total 54 marks

Name

Class

Date

1
A student in Wellington adds sodium hydrogencarbonate to vinegar in a conical flask standing on a balance, with cotton wool in the neck of the flask. Carbon dioxide escapes and the mass reading falls. The readings are 120.00 g at 0 s, 119.70 g at 30 s, 119.52 g at 60 s, 119.42 g at 90 s, 119.40 g at 120 s and 119.40 g at 150 s.
(a)
How can the student tell that the reaction has finished?
[1 mark]
AThe mass reading is still falling quickly
BThe mass reading starts to rise again
CThe mass reading fell by the largest amount in the first 30 s
DThe mass reading no longer changes
(b)
What is the mean rate of mass loss in the first 30 seconds?
[1 mark]
A0.30 g s⁻¹
B0.010 g s⁻¹
C9.0 g s⁻¹
D100 g s⁻¹
(c)
Calculate the mean rate of mass loss between 30 s and 90 s, in g s⁻¹.
[2 marks]
Total for question 1: 4 marks
2
In a flour mill in Punjab, a heap of flour on the floor hardly burns, but fine flour dust in the air can explode violently if a spark lands in it. The flour dust reacts with oxygen in the air. The mill is warm, at about 35 °C.
(a)
Which action would reduce the rate of reaction between flour dust and oxygen?
[1 mark]
AKeeping the air in the mill cool
BGrinding the flour more finely
CStirring the dust into the air
DAdding a catalyst
(b)
A spark makes the flour dust explode. What does the spark provide?
[1 mark]
AA catalyst for the reaction
BA higher concentration of oxygen
CEnergy so that colliding particles can reach the activation energy
DMore surface area for the flour
(c)
Explain, in terms of collisions, why flour dust reacts much faster with oxygen than a heap of flour.
[2 marks]
Total for question 2: 4 marks
3
Students in Vancouver test the hypothesis that manganese(IV) oxide, MnO₂, speeds up the decomposition of hydrogen peroxide solution: 2H₂O₂ → 2H₂O + O₂. They add the same volume of the same hydrogen peroxide solution to two flasks, add 1.00 g of manganese(IV) oxide powder to one flask and nothing to the other, and collect the oxygen in a gas syringe for 2 minutes. Safety glasses are worn.
(a)
Identify the independent variable, the dependent variable and one control variable in this investigation.
[3 marks]
(b)
With manganese(IV) oxide the flask produced 80 cm³ of oxygen in the first 30 s and 96 cm³ in total. The flask without it produced only 4 cm³ in 2 minutes. After the reaction the manganese(IV) oxide was filtered off, dried and weighed, and its mass was still 1.00 g. Evaluate the hypothesis using these results, explain in terms of activation energy how a catalyst speeds up a reaction, explain what the final mass shows, and suggest one improvement to the method.
[4 marks]
Total for question 3: 7 marks
4
In Mexico City, cars must have a catalytic converter in the exhaust. The converter is a ceramic honeycomb coated with a thin layer of platinum. Hot exhaust gases flow through it, and harmful gases such as carbon monoxide and nitrogen monoxide react to form carbon dioxide and nitrogen. Platinum is a rare and expensive metal that has to be mined. The city is deciding whether to require all older vehicles, including motorcycles, to fit a converter.
(a)
Explain, using collision theory, how the catalytic converter speeds up the removal of harmful gases from the exhaust.
[6 marks]
(b)
Discuss the benefits and drawbacks of requiring all older vehicles to fit a catalytic converter, and reach a justified conclusion.
[6 marks]
Total for question 4: 12 marks
5
In a sealed bottle of sparkling water in Warsaw, carbon dioxide gas in the space above the drink dissolves in the water, while dissolved carbon dioxide also escapes back into the gas. The bottle is kept at a constant temperature. The change can be written CO₂(g) ⇌ CO₂(aq).
(a)
Which statement describes the system once it has reached equilibrium?
[1 mark]
ACarbon dioxide has stopped dissolving
BCarbon dioxide dissolves and escapes at the same rate
CAll the carbon dioxide has dissolved
DCarbon dioxide escapes faster than it dissolves
(b)
Why must the bottle be sealed for equilibrium to be reached?
[1 mark]
ATo keep the temperature constant
BTo stop the water evaporating
CTo lower the pressure inside the bottle
DTo stop carbon dioxide leaving the system so that both changes can continue
(c)
Explain why the drink fizzes more when the bottle is opened.
[2 marks]
Total for question 5: 4 marks
6
In a village in Kenya, a family notices that fresh milk turns sour within a day on the kitchen table at 25 °C, but stays fresh for several days in a refrigerator at 4 °C. The souring happens because bacteria use enzymes, which are biological catalysts, to turn lactose into lactic acid. In a test, the pH of milk at 25 °C fell from 6.7 to 5.0 in 24 hours.
(a)
Why does milk sour more slowly at 4 °C than at 25 °C?
[1 mark]
AThe particles move faster, so fewer of them collide
BThere are more particles in the milk at 4 °C
CThe particles move more slowly, so fewer collisions have enough energy to react
DThe activation energy of the reaction is higher at 4 °C
(b)
How do the enzymes speed up the souring reaction?
[1 mark]
AThey provide an alternative pathway with a lower activation energy
BThey increase the temperature of the milk
CThey are used up as the reaction happens
DThey increase the activation energy
(c)
Calculate the mean rate of change of pH at 25 °C, in pH units per hour.
[2 marks]
Total for question 6: 4 marks
7
A technician in Pretoria heats a little white ammonium chloride at the bottom of a test tube. The white solid disappears from the bottom, and a white solid forms on the cooler upper part of the tube. The change can be written NH₄Cl(s) ⇌ NH₃(g) + HCl(g).
(a)
Explain these observations.
[3 marks]
(b)
The technician now considers heating ammonium chloride in a closed container kept at a constant high temperature. Describe and explain what happens until the amounts of the substances stop changing, and explain why this state is called a dynamic equilibrium.
[4 marks]
Total for question 7: 7 marks
8
Ammonia is made from nitrogen and hydrogen in the Haber process: N₂(g) + 3H₂(g) ⇌ 2NH₃(g). The forward reaction is exothermic. A typical plant runs at about 450 °C and 200 atmospheres pressure, with an iron catalyst. More than 150 million tonnes of ammonia are made each year, mostly for fertilisers that help to feed billions of people. The hydrogen is usually made from natural gas, and ammonia production causes about 1–2% of the world's carbon dioxide emissions.
(a)
Explain why the plant uses a temperature of 450 °C, a pressure of 200 atmospheres and an iron catalyst.
[6 marks]
(b)
Discuss the benefits and drawbacks of continuing to make ammonia fertiliser by the Haber process, and reach a justified conclusion.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).