Rates of Reaction & Energy ChangesEdexcel GCSE Chemistry: Topic test

20 questions, 54 marks

Edexcel GCSE Chemistry

Rates of Reaction & Energy Changes topic test

Total 54 marks

Name

Class

Date

1
A student places 50 cm3 of dilute sulfuric acid into a conical flask standing on an electronic balance, plugs the flask with cotton wool, and adds 2.0 g of powdered sodium carbonate. She records the total mass of the flask and its contents every 10 seconds for 3 minutes, as carbon dioxide gas escapes through the cotton wool plug.
(a)
Which quantity decreases as the reaction proceeds, allowing the rate of this reaction to be measured?
[1 mark]
AThe total mass of the flask and its contents, as carbon dioxide gas escapes
BThe temperature of the reaction mixture
CThe volume of unreacted acid remaining in the flask
DThe concentration of the sodium carbonate powder before it is added
(b)
The student repeats the experiment using the same mass of sodium carbonate but in large lumps instead of powder, keeping everything else the same. Which statement correctly predicts and explains the effect on the rate of reaction?
[1 mark]
AThe reaction will be faster with lumps, because lumps contain more sodium carbonate particles overall
BThe reaction will be slower with lumps, because their surface area to volume ratio is smaller, so fewer collisions between acid and sodium carbonate particles occur per second
CThe rate of reaction will be exactly the same, since the total mass of sodium carbonate is unchanged
DThe reaction will stop completely, since lumps of solid cannot react with an acid at all
(c)
Explain, in terms of collision theory, why increasing the concentration of the sulfuric acid would increase the rate of this reaction.
[2 marks]
Total for question 1: 4 marks
2
A physiotherapist uses an instant cold pack containing solid ammonium nitrate in a sealed inner pouch of water. When the pack is squeezed, the inner pouch breaks and the ammonium nitrate dissolves in the water. A thermometer taped to the outside of the pack shows the temperature falling from 21 degrees Celsius to 4 degrees Celsius within a minute.
(a)
What type of change is occurring as the ammonium nitrate dissolves in the water in the cold pack?
[1 mark]
AAn exothermic change
BA physical change with no transfer of heat energy at all
CAn endothermic change
DA nuclear change
(b)
Which statement correctly explains, in terms of bond/attraction breaking and forming, why this dissolving process causes the temperature to fall?
[1 mark]
AMore heat energy is released when new bonds form in the products than is absorbed when bonds are broken in the reactants, so the temperature rises
BDissolving is a purely physical mixing process, with no bonds or attractions broken or formed at all
CHeat energy is transferred from the surroundings to the pack only by conduction, unrelated to any chemical or physical process
DMore heat energy is absorbed in breaking apart the ammonium nitrate lattice (and some water interactions) than is released in forming new attractions between the ions and water molecules, so heat energy is taken in overall from the surroundings
(c)
Define the term 'endothermic', and use it to explain why the cold pack feels cold to touch.
[2 marks]
Total for question 2: 4 marks
3
A student reacts small chips of calcium carbonate with an excess of dilute ethanoic acid in a conical flask connected to a gas syringe, and records the volume of carbon dioxide gas collected every 15 seconds until the reaction finishes after 4 minutes, producing a total of 240 cm3 of gas.
(a)
Describe, in words, the shape of a graph of volume of gas collected against time for this reaction, and state how the rate of reaction at any point could be found from such a graph.
[3 marks]
(b)
Explain, in terms of collision theory, why the rate of this reaction is fastest at the start and gradually decreases as the reaction proceeds, even though the temperature remains constant throughout.
[4 marks]
Total for question 3: 7 marks
4
A company manufactures disposable hand warmers containing iron powder, water, salt and activated carbon sealed inside a small fabric pouch. When the pouch is exposed to air, oxygen diffuses in and reacts with the iron powder, releasing heat steadily for several hours. The company is testing whether using a finer iron powder, instead of coarser iron filings, changes how the hand warmer performs.
(a)
Explain, in terms of energy transferred when bonds break and form, why the reaction between iron and oxygen in the hand warmer is exothermic, describe, in words, how the energy of the products compares with the energy of the reactants, and explain what is meant by the activation energy of this reaction.
[6 marks]
(b)
Explain why using a finer iron powder, rather than coarser iron filings, would be expected to change the rate at which the hand warmer heats up, and evaluate whether this would make a finer-powder hand warmer more suitable for a customer who wants gentle, long-lasting warmth over several hours, rather than a rapid burst of heat.
[6 marks]
Total for question 4: 12 marks
5
A car manufacturer fits a catalytic converter containing platinum and palladium catalysts into a car's exhaust system. The catalysts speed up the reaction that converts toxic carbon monoxide and nitrogen oxide gases from the engine into less harmful carbon dioxide and nitrogen gases, without the catalysts themselves being used up.
(a)
Which statement correctly describes how the platinum and palladium catalysts increase the rate of this reaction?
[1 mark]
AThe catalysts increase the temperature of the exhaust gases, which speeds up the reaction
BThe catalysts increase the concentration of the toxic gases entering the exhaust system
CThe catalysts react permanently with the toxic gases and are used up as the reaction proceeds
DThe catalysts provide an alternative reaction pathway with a lower activation energy, so a greater proportion of colliding particles have enough energy to react
(b)
Which statement about the platinum and palladium catalysts in the converter is correct?
[1 mark]
AThey are used up in the reaction and must be replaced after a single journey
BThey become chemically incorporated into the carbon dioxide and nitrogen products permanently
CThey remain chemically unchanged and the same mass at the end of the reaction, so a small amount can catalyse a very large number of reactions
DThey slow down unwanted side reactions but have no effect on the rate of the desired reaction
(c)
Explain what is meant by the term 'catalyst', and explain one advantage, other than speed, of the catalytic converter lowering the activation energy of this reaction rather than the reaction being sped up by further increasing the temperature of the exhaust gases.
[2 marks]
Total for question 5: 4 marks
6
A student adds excess magnesium ribbon to 25 cm3 of copper sulfate solution held in a well-insulated calorimeter, wrapped in cotton wool and fitted with a lid. She records a temperature rise from 19 degrees Celsius to 52 degrees Celsius, as a red-brown solid forms and the blue colour of the solution fades.
(a)
What type of change is occurring in this displacement reaction, based on the temperature change observed?
[1 mark]
AAn endothermic change, since heat energy is taken in
BAn exothermic change, since heat energy is given out
CNeither exothermic nor endothermic; the temperature change is unrelated to the reaction
DA nuclear change, involving a change in the copper nucleus
(b)
Which statement correctly explains, in terms of bond/attraction breaking and forming, why this reaction is exothermic?
[1 mark]
AMore energy is released when new bonds/attractions form in the products (magnesium sulfate solution and copper) than is required to break the bonds/attractions in the reactants, so energy is given out overall
BMore energy is required to break bonds/attractions in the reactants than is released forming the products, so energy is given out overall
CNo bonds or attractions are broken or formed in this reaction, since displacement reactions are purely physical changes
DThe temperature rises only because of friction from stirring the solution, unrelated to any chemical process
(c)
Explain why the student wraps the calorimeter in cotton wool and uses a lid during this experiment.
[2 marks]
Total for question 6: 4 marks
7
A camper uses a small butane gas lighter. A spark from the flint ignites the gas, which then burns steadily with a small, hot flame, releasing energy that heats the camper's food. Without the initial spark, the butane gas does not ignite by itself, even though it is flammable.
(a)
State whether the combustion of butane is exothermic or endothermic, and explain, in terms of energy, why the initial spark from the flint is needed to start the reaction even though the overall reaction gives out energy.
[3 marks]
(b)
Describe, in words, how the energy of the reactants and products would compare in a reaction profile for this exothermic combustion reaction, and explain what activation energy represents on such a profile.
[4 marks]
Total for question 7: 7 marks
8
A pharmaceutical lab studies the reaction between powdered citric acid and sodium bicarbonate, used in effervescent tablets, which is endothermic and produces carbon dioxide gas. Researchers compare tablets made with finely powdered ingredients against tablets made with coarser granules, timing how long each type takes to fully dissolve and stop fizzing in a glass of water, and measuring the temperature drop of the water in each case.
(a)
Explain, in terms of collision theory, why the finely powdered tablet is expected to stop fizzing more quickly than the coarser-granule tablet, and explain, in terms of bond breaking and bond making, why the reaction is endothermic, causing the water temperature to fall.
[6 marks]
(b)
Evaluate whether measuring the time taken for each tablet to stop fizzing, or measuring the temperature drop of the water, is the more reliable way of comparing the rate of reaction between the powdered and granular tablets, and suggest one improvement to make the comparison fairer.
[6 marks]
Total for question 8: 12 marks

End of questions