Revision Library

revisionlibrary.co.uk

13+ · Chemistry

CE.S-C4 Chemistry: Reactions, Energy and Rates

ISEB CE ISEB CE 13+ Science (Chemistry) · Calculator allowed · about 60 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

Different types of chemical reaction have specific names.

(a)State the type of reaction that takes place when a fuel burns in oxygen.(1)

(b)State the type of reaction between an acid and an alkali.(1)

(c)State the type of reaction in which a compound is broken down into two or more simpler substances using heat.(1)

(d)State the type of reaction in which a substance gains oxygen.(1)

(Total for Question 1 is 4 marks)

Vinegar, soap solution and pure water are common substances found at home.

(a)State whether vinegar is acidic, alkaline or neutral.(1)

(b)State whether soap solution is acidic, alkaline or neutral.(1)

(c)State whether pure water is acidic, alkaline or neutral.(1)

(d)Zainab has indigestion caused by excess acid in her stomach. She takes an indigestion tablet containing magnesium hydroxide, an alkali. Explain, using the word 'neutralisation', how the tablet relieves her indigestion.(2)

(Total for Question 2 is 5 marks)

Complete combustion happens when a fuel burns in a plentiful supply of oxygen.

(a)Write a word equation for the complete combustion of methane.(2)

(b)Write a word equation for magnesium burning in oxygen.(2)

(Total for Question 3 is 4 marks)

Tariq heats a piece of shiny copper foil strongly in a Bunsen flame. The copper turns black.

(a)Write a word equation for the reaction between copper and oxygen.(2)

(b)Explain, in terms of oxygen, why this reaction is called oxidation.(2)

(Total for Question 4 is 4 marks)

All chemical reactions involve an energy change.

(a)Define the term exothermic reaction.(1)

(b)Define the term endothermic reaction.(1)

(c)State whether combustion is exothermic or endothermic.(1)

(d)State whether the thermal decomposition of calcium carbonate is exothermic or endothermic.(1)

(Total for Question 5 is 4 marks)

The rate of a chemical reaction can be changed by several factors.

(a)State three factors, other than using a catalyst, that affect the rate of a chemical reaction.(3)

(b)State what a catalyst does to the rate of a reaction.(1)

(Total for Question 6 is 4 marks)

Aluminium reacts with dilute hydrochloric acid.

(a)Write a word equation for this reaction.(2)

(b)Describe a test for the gas produced, including the result of a positive test.(2)

(Total for Question 7 is 4 marks)

Sodium carbonate reacts with dilute nitric acid.

(a)Write a word equation for this reaction.(2)

(b)Describe a test for the gas produced, including the result of a positive test.(2)

(Total for Question 8 is 4 marks)

Farmers sometimes spread powdered lime (calcium oxide or calcium carbonate) on fields where the soil is too acidic for crops to grow well.

(a)Write the general word equation for a neutralisation reaction between an acid and an alkali.(2)

(b)Explain why spreading lime on acidic soil helps crops to grow better.(2)

(c)Suggest one other everyday use of a neutralisation reaction.(1)

(Total for Question 9 is 5 marks)

Hydrocarbon fuels such as methane can undergo complete or incomplete combustion, depending on the supply of oxygen.

(a)State the two products formed when a hydrocarbon fuel undergoes complete combustion.(2)

(b)State one other substance, besides carbon monoxide, that can be produced when a hydrocarbon fuel undergoes incomplete combustion.(1)

(c)Explain why incomplete combustion of a gas fire in a poorly ventilated room can be dangerous.(2)

(Total for Question 10 is 5 marks)

Increasing the temperature of a reaction mixture increases the rate of reaction.

(a)Using ideas about particles, explain why increasing the temperature increases the rate of reaction.(3)

(Total for Question 11 is 3 marks)

Amara investigates how the surface area of marble chips (calcium carbonate) affects the rate of its reaction with dilute hydrochloric acid. She reacts large marble chips with acid in one experiment, and the same total mass of small marble chips with acid in a second experiment, measuring the volume of gas produced using a gas syringe.

(a)State the independent variable in this investigation.(1)

(b)State the dependent variable in this investigation.(1)

(c)State two variables that should be kept the same in both experiments to make this a fair test.(2)

(d)Predict which experiment would show the faster initial rate of reaction, and explain your prediction in terms of particles.(2)

(Total for Question 12 is 6 marks)

Aisha mixes two chemicals together in a polystyrene cup and measures the temperature of the mixture every 30 seconds.
Time (s): 0, 30, 60, 90, 120, 150
Temperature (C): 18.0, 21.5, 24.0, 25.5, 25.5, 25.5

(a)Calculate the rise in temperature during the experiment.(2)

(b)State, giving a reason from the data, whether this reaction is exothermic or endothermic.(2)

(c)Suggest why the temperature stopped changing after 90 seconds.(1)

(d)Suggest one improvement Aisha could make to her method to reduce heat loss to the surroundings.(1)

(Total for Question 13 is 6 marks)

Ravi investigates how the concentration of sodium thiosulfate solution affects the rate of its reaction with dilute hydrochloric acid. He places each mixture in a flask over a piece of paper marked with a black cross, and times how long it takes until the cross can no longer be seen through the cloudy sulfur produced.
Concentration of sodium thiosulfate (g/dm³): 10, 20, 30, 40
Time for cross to disappear (s): 100, 50, 33, 25

(a)Describe how the time taken for the cross to disappear changes as the concentration of sodium thiosulfate increases.(2)

(b)Explain, in terms of particles, why increasing the concentration of sodium thiosulfate increases the rate of reaction.(2)

(c)The rate of reaction can be estimated using rate = 1 / time. Calculate the rate of reaction at a concentration of 20 g/dm³, in s^-1. Give your answer to 3 significant figures.(3)

(d)State one variable that should be kept constant in this investigation, other than the concentration of sodium thiosulfate.(1)

(Total for Question 14 is 8 marks)

In an exothermic reaction, the products have less energy than the reactants. The minimum energy that particles need to react when they collide is called the activation energy.

(a)State whether the products have more or less energy than the reactants in an exothermic reaction.(1)

(b)Define the term activation energy.(1)

(c)A catalyst lowers the activation energy of a reaction. Explain how this increases the rate of reaction.(2)

(Total for Question 15 is 4 marks)

A group of students, including Chidi and Sofia, repeat the disappearing cross experiment three times at the same concentration of sodium thiosulfate and record the times: 42 s, 71 s, 44 s.

(a)Identify the anomalous result.(1)

(b)Suggest one possible reason why this result might be anomalous.(1)

(c)Explain why the anomalous result should not be included when calculating a mean, and calculate the mean time using the two remaining readings.(2)

(d)Suggest one way the group could improve the reliability of their results.(1)

(Total for Question 16 is 5 marks)

A student wants to investigate the effect of temperature on the rate of reaction between sodium thiosulfate solution and dilute hydrochloric acid, using the disappearing cross method. Describe how the student could carry out this investigation, including the measurements taken and how a fair test would be ensured.

(Total for Question 17 is 6 marks)

Deepa and Liam each react a small strip of magnesium ribbon with excess dilute hydrochloric acid and measure the volume of hydrogen gas produced over time. Deepa uses 1 mol/dm³ acid (Experiment A). Liam uses 2 mol/dm³ acid (Experiment B). Both experiments are carried out at the same temperature, using identical, excess volumes of acid and identical pieces of magnesium.

(a)Predict which experiment, A or B, would produce gas at the faster initial rate. Explain your answer in terms of particles.(2)

(b)The magnesium is the limiting reactant in both experiments (the acid is in excess). State what this tells you about the total volume of gas produced by the end of each experiment, and explain your answer.(2)

(c)On a graph of volume of gas produced against time, state how the curve for Experiment B would differ in shape from the curve for Experiment A.(2)

(Total for Question 18 is 6 marks)

Balance the following symbol equations for combustion reactions.

(a)CH4 + O2 -> CO2 + H2O(2)

(b)Mg + O2 -> MgO(2)

(Total for Question 19 is 4 marks)

Mark scheme · CE.S-C4 Chemistry: Reactions, Energy and Rates

Question 1

(a) B1 combustion, cso
(a) Answer: Combustion
(b) B1 neutralisation, cso
(b) Answer: Neutralisation
(c) B1 thermal decomposition, cso (accept decomposition)
(c) Answer: Thermal decomposition
(d) B1 oxidation, cso
(d) Answer: Oxidation

Question 2

(a) B1 acidic, cao
(a) Answer: Acidic
(b) B1 alkaline, cao
(b) Answer: Alkaline
(c) B1 neutral, cao
(c) Answer: Neutral
(d) B1 the alkali (magnesium hydroxide) reacts with and neutralises the excess acid in her stomach, oe
(d) B1 this reduces the acidity/raises the pH of her stomach contents back towards neutral, which relieves the indigestion, oe
(d) Answer: The magnesium hydroxide (alkali) neutralises the excess acid in her stomach, reducing the acidity and raising the pH back towards neutral, which relieves the pain.

Question 3

(a) B1 methane + oxygen ->
(a) B1 carbon dioxide + water, both needed
(a) Answer: methane + oxygen -> carbon dioxide + water
(b) B1 magnesium + oxygen ->
(b) B1 magnesium oxide, cao
(b) Answer: magnesium + oxygen -> magnesium oxide

Question 4

(a) B1 copper + oxygen ->
(a) B1 copper oxide, cao
(a) Answer: copper + oxygen -> copper oxide
(b) B1 oxidation is defined as a reaction in which a substance gains oxygen, oe
(b) B1 the copper gains/combines with oxygen from the air to form copper oxide, oe
(b) Answer: Oxidation is a reaction in which a substance gains oxygen; the copper gains oxygen from the air to form copper oxide, so it has been oxidised.

Question 5

(a) B1 a reaction that transfers/releases energy (heat) to the surroundings, causing the temperature of the surroundings to increase, oe
(a) Answer: A reaction that transfers energy to the surroundings, so the temperature of the surroundings increases.
(b) B1 a reaction that takes in/absorbs energy (heat) from the surroundings, causing the temperature of the surroundings to decrease, oe
(b) Answer: A reaction that takes in energy from the surroundings, so the temperature of the surroundings decreases.
(c) B1 exothermic, cao
(c) Answer: Exothermic
(d) B1 endothermic, cao
(d) Answer: Endothermic

Question 6

(a) B1 temperature
(a) B1 concentration (of a solution) or pressure (of a gas)
(a) B1 surface area/particle size of a solid reactant
(a) Answer: Temperature, concentration (or pressure), and surface area (particle size) of a solid reactant.
(b) B1 it speeds up (increases) the rate of reaction without being used up (chemically unchanged) itself, oe
(b) Answer: It speeds up the reaction without being used up itself.

Question 7

(a) B1 aluminium + hydrochloric acid ->
(a) B1 aluminium chloride + hydrogen, both needed
(a) Answer: aluminium + hydrochloric acid -> aluminium chloride + hydrogen
(b) B1 hold a lit/burning splint at the mouth of the test tube, oe
(b) B1 the gas ignites/burns with a squeaky pop, oe
(b) Answer: Hold a lit splint at the mouth of the test tube; the gas ignites with a squeaky pop.

Question 8

(a) B1 sodium carbonate + nitric acid ->
(a) B1 sodium nitrate + water + carbon dioxide, all needed
(a) Answer: sodium carbonate + nitric acid -> sodium nitrate + water + carbon dioxide
(b) B1 bubble the gas through limewater, oe
(b) B1 the limewater turns cloudy/milky, oe
(b) Answer: Bubble the gas through limewater; the limewater turns cloudy/milky.

Question 9

(a) B1 acid + alkali ->
(a) B1 salt + water
(a) Answer: acid + alkali -> salt + water
(b) B1 the lime is a base and neutralises the excess acid in the soil, oe
(b) B1 this raises the pH of the soil towards neutral, which suits most crops better than acidic soil, oe
(b) Answer: The lime neutralises the excess acid in the soil, raising its pH towards neutral, which suits most crops better than acidic soil.
(c) B1 any sensible example, e.g. toothpaste neutralising acid produced by bacteria in the mouth, or an indigestion tablet neutralising excess stomach acid, oe
(c) Answer: Example: toothpaste neutralising acid produced by bacteria in the mouth, protecting tooth enamel.

Question 10

(a) B1 carbon dioxide
(a) B1 water
(a) Answer: Carbon dioxide and water
(b) B1 carbon/soot, cao
(b) Answer: Carbon (soot)
(c) B1 incomplete combustion (due to insufficient oxygen) produces carbon monoxide gas, oe
(c) B1 carbon monoxide is toxic because it combines with haemoglobin in the blood, reducing the amount of oxygen the blood can carry around the body, oe
(c) Answer: Incomplete combustion produces carbon monoxide, a toxic gas that binds to haemoglobin in the blood and reduces the amount of oxygen the blood can carry, which can be fatal.

Question 11

(a) B1 particles move faster/have more kinetic energy at a higher temperature, oe
(a) B1 so particles collide with each other more frequently, oe
(a) B1 and a greater proportion of collisions have enough energy (at least the activation energy) to react, so more collisions are successful, oe
(a) Answer: At a higher temperature, particles move faster and collide more often, and a greater proportion of these collisions have enough energy to be successful, so the rate of reaction increases.

Question 12

(a) B1 the surface area (particle size) of the marble chips, cao
(a) Answer: The surface area (particle size) of the marble chips
(b) B1 the volume of gas produced (or the rate of gas production), cao
(b) Answer: The volume of gas produced (or rate of gas production)
(c) B1 any one of: total mass of marble chips, volume and concentration of acid, temperature
(c) B1 a second, different correct variable from the list above
(c) Answer: Any two of: total mass of marble chips, volume and concentration of the acid, temperature.
(d) B1 the small chips (larger total surface area), cao
(d) B1 a larger surface area exposes more particles of the marble to the acid, so collisions between acid and marble particles happen more frequently, oe
(d) Answer: The small chips, because breaking the marble into smaller pieces increases its total surface area, exposing more particles to the acid and increasing the frequency of collisions.

Question 13

(a) M1 25.5 - 18.0, oe
(a) A1 7.5 (C), cao
(a) Answer: 7.5C
(b) B1 exothermic, cao
(b) B1 because the temperature of the mixture increased, showing that energy was released to the surroundings, oe
(b) Answer: Exothermic, because the temperature increased, showing energy was released to the surroundings.
(c) B1 the reaction had finished (one of the reactants had been completely used up), oe
(c) Answer: The reaction had finished, so no more energy was being released.
(d) B1 put a lid on the polystyrene cup, or wrap/insulate the cup (e.g. with cotton wool), oe
(d) Answer: Put a lid on the cup (or insulate the cup with cotton wool) to reduce heat loss.

Question 14

(a) B1 the time taken decreases as the concentration increases, oe
(a) B1 so the rate of reaction increases as the concentration increases, oe
(a) Answer: As the concentration increases, the time taken for the cross to disappear decreases, showing that the rate of reaction increases with concentration.
(b) B1 at a higher concentration there are more sodium thiosulfate particles in the same volume of solution, oe
(b) B1 so collisions between sodium thiosulfate and acid particles happen more frequently, increasing the rate, oe
(b) Answer: A higher concentration means more sodium thiosulfate particles are packed into the same volume, so collisions between the reacting particles happen more often, increasing the rate.
(c) M1 identifies the correct time for 20 g/dm³, 50 (s)
(c) dM1 1 / their 50
(c) A1 0.0200 s^-1, awrt
(c) Answer: 0.0200 s^-1
(d) B1 any one of: volume of sodium thiosulfate solution, volume/concentration of hydrochloric acid, temperature, the same flask/cross viewed from the same position
(d) Answer: Example: the temperature of the solutions.

Question 15

(a) B1 less, cao
(a) Answer: Less
(b) B1 the minimum energy that particles must have when they collide in order to react, oe
(b) Answer: The minimum energy that colliding particles need for a reaction to occur.
(c) B1 with a lower activation energy, more particles already have enough energy to react when they collide, oe
(c) B1 so a greater proportion of collisions are successful, increasing the rate of reaction, oe
(c) Answer: Lowering the activation energy means more particles already have enough energy to react when they collide, so a greater proportion of collisions are successful, increasing the rate.

Question 16

(a) B1 71 (s), cao
(a) Answer: 71 s
(b) B1 any sensible procedural error, e.g. the stopwatch was started or stopped at the wrong moment, the cross was viewed from a different angle/height, or the flask was not clean, oe
(b) Answer: Example: the stopwatch may have been started or stopped at the wrong moment.
(c) M1 excludes 71 (s) because it does not agree with (is not close to) the other two readings, oe, and adds 42 + 44
(c) A1 43 (s), cao, ft their identified anomaly excluded
(c) Answer: 43 s (the anomalous 71 s is excluded because it disagrees with the other two consistent readings; mean = (42 + 44) / 2 = 43 s).
(d) B1 repeat the experiment more times (e.g. a fourth repeat) and calculate a mean from all the consistent readings, oe
(d) Answer: Take more repeat readings and calculate a mean from the consistent results.

Question 17

Level 1 (1-2): Basic, isolated statements about heating the solution and timing, with little or no detail on method, measurements or fair test.
Level 2 (3-4): A reasonable method is described, including heating or cooling the solution to different temperatures and timing until the cross disappears, with some attempt to keep other variables constant, though detail may be incomplete.
Level 3 (5-6): A clear, logical, detailed method describing how to vary and measure the temperature, how the disappearance of the cross is used to measure rate, and how the volumes/concentrations of both solutions, the flask, the cross and the observer are kept constant across repeats, using accurate scientific vocabulary throughout.
Indicative content:
- Use the same volume and concentration of sodium thiosulfate solution and the same volume and concentration of hydrochloric acid in each repeat.
- Heat (or cool) the sodium thiosulfate solution in a water bath to the required temperature and measure its temperature with a thermometer before adding the acid.
- Place the flask on a piece of paper marked with a black cross, viewed from above.
- Add the acid to the sodium thiosulfate, swirl to mix, and immediately start a stopwatch/timer.
- Look down through the solution and stop the timer as soon as the cross can no longer be seen through the cloudy sulfur produced.
- Record the time taken at that temperature.
- Repeat the experiment at several different temperatures (e.g. every 10C), keeping the same flask, the same observer/viewing position and the same volumes each time.
- Repeat each temperature at least once more and calculate a mean time.
- Plot a graph of temperature against time (or temperature against 1/time as a measure of rate) to see the trend.

Question 18

(a) B1 Experiment B, cao
(a) B1 the more concentrated acid has more acid particles in the same volume, so collisions between acid and magnesium particles happen more frequently, oe
(a) Answer: Experiment B, because the higher concentration of acid means more acid particles per unit volume, leading to more frequent collisions with the magnesium and a faster initial rate.
(b) B1 the same total volume of gas is produced in both experiments, oe
(b) B1 because the same mass/amount of magnesium reacts completely in each case, and the total amount of gas produced depends on the amount of magnesium (the limiting reactant), not on the rate of reaction, oe
(b) Answer: The same total volume of gas is produced in both, because the same amount of magnesium (the limiting reactant) reacts completely each time; concentration affects the rate, not the total amount of product formed.
(c) B1 the curve for B would rise more steeply (be steeper) at the start than the curve for A, oe
(c) B1 and would level off (reach its maximum volume) sooner than the curve for A, but at the same final (maximum) volume, oe
(c) Answer: The curve for Experiment B would rise more steeply at first and level off sooner than Experiment A's curve, but both curves would level off at the same final volume of gas.

Question 19

(a) M1 attempts to balance hydrogen or oxygen atoms on each side
(a) A1 CH4 + 2O2 -> CO2 + 2H2O, cao
(a) Answer: CH4 + 2O2 -> CO2 + 2H2O
(b) M1 attempts to balance magnesium or oxygen atoms on each side
(b) A1 2Mg + O2 -> 2MgO, cao
(b) Answer: 2Mg + O2 -> 2MgO

Chemistry: Reactions, Energy and Rates - Worksheets, Questions and Revision