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Rates of Reaction and Energy Changes — Free MYP5 Chemistry Practice Questions
1QuestionEnergy transfer between system and surroundingsConcept Practice
2 marks~3 minCriterion A
A student dissolves ammonium nitrate in water inside a beaker. The thermometer reads , while the surrounding air is at . The beaker feels cold to the touch, and arrows on the diagram show energy transferring from the surroundings into the reaction mixture.
a
Deduce the direction of energy transfer between the surroundings and the reaction mixture. [1]
b
Justify the classification of this reaction as endothermic, using the temperature data provided. [1]
Solutions
2QuestionInterpreting energy diagrams (peaks, energy levels)Concept Practice
4 marks~6 minCriterion A
The energy profile below represents a chemical reaction.
Diagram description: Reactants at , transition state (peak) at , products at . The x-axis is labelled "Reaction progress" and the y-axis "Potential energy (kJ)". Arrow A runs from reactants to the peak; Arrow B runs from the peak to products; Arrow C runs from reactants to products.
Diagram description: Reactants at , transition state (peak) at , products at . The x-axis is labelled "Reaction progress" and the y-axis "Potential energy (kJ)". Arrow A runs from reactants to the peak; Arrow B runs from the peak to products; Arrow C runs from reactants to products.
a
Identify which arrow (A, B, or C) represents the activation energy of this reaction. [1]
b
Deduce the overall energy change of the reaction, in kJ, and state whether energy is released or absorbed. [1]
c
The products of this reaction are described as thermodynamically more stable than the reactants. Using values from the diagram, explain how the energy profile supports this claim. [2]
Solutions
3QuestionConditions for successful collisions (energy + orientation)Concept Practice
3 marks~5 minCriterion A
The reaction profile below shows energy changes for a reaction proceeding with and without a catalyst.
a
Explain what a catalyst does to the reaction pathway that results in a lower activation energy. [1]
b
Explain, using collision theory, what condition must be met for a collision between reactant particles to be successful. [1]
c
Analyse how the lower activation energy of the catalysed pathway affects the proportion of successful collisions among reactant particles. [1]
Solutions
4QuestionCatalysts and lowering activation energyConcept Practice
2 marks~3 minCriterion A
The reaction profile diagram below shows two curves, A and B, for the same chemical reaction. Curve A has a higher energy peak than Curve B. The energy difference between the reactants and the peak of Curve A is labelled .
a
Deduce which curve, A or B, represents the catalysed reaction. [1]
b
Explain how a catalyst enables more reactant molecules to form products, with reference to the energy labelled . [1]
Solutions
5QuestionClosed system requirement for equilibriumConcept Practice
3 marks~5 minCriterion A
The diagram shows two sealed flasks and one open flask containing the reversible reaction:
(brown) (colourless)
Flask A is sealed with a stopper. Flask B is open to the atmosphere.
(brown) (colourless)
Flask A is sealed with a stopper. Flask B is open to the atmosphere.
a
Identify which flask can achieve dynamic equilibrium. [1]
b
Explain why Flask B cannot achieve dynamic equilibrium, using the concept of a closed system. [2]
Solutions
6QuestionTemperature changes during reactionsAssessment Practice
5 marks~8 minCriterion B
A student adds 1.0 g samples of five metals to 50 cm³ of 1.0 mol/dm³ hydrochloric acid in a polystyrene cup, recording the maximum temperature change () for each:
An unknown metal X, tested under identical conditions, gives °C.
| Metal | magnesium | zinc | iron | copper | silver |
|---|---|---|---|---|---|
| (°C) | +24.5 | +12.0 | +5.5 | 0.0 | 0.0 |
An unknown metal X, tested under identical conditions, gives °C.
a
State the type of energy change occurring when a reactive metal is added to hydrochloric acid, and write the general word equation for the reaction. [1]
b
Explain how the data above show a relationship between a metal's reactivity and its observed , referring to at least three metals in your answer. [2]
c
Deduce the identity of metal X. Justify your answer using both the data and the reactivity series. [2]
Solutions
7QuestionDefinition of endothermic vs exothermic reactionsAssessment Practice
5 marks~8 minCriterion C
A student mixes 50 cm³ of 1.0 mol dm⁻³ HCl with 50 cm³ of 1.0 mol dm⁻³ NaOH in a polystyrene cup and records the temperature every 30 seconds.
| Time (s) | 0 | 30 | 60 | 90 | 120 | 150 | 180 | 210 | 240 | 270 | 300 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Temperature (°C) | 22.0 | 26.5 | 29.8 | 31.2 | 31.5 | 31.0 | 30.2 | 29.1 | 28.0 | 27.0 | 26.2 |
a
State whether the reaction is endothermic or exothermic. Give one piece of evidence from the data to support your answer. [1]
b
Explain the shape of the temperature–time graph between 0 s and 120 s, and between 120 s and 300 s. [2]
c
Analyse why the temperature decrease after 120 s does not indicate an endothermic process, and evaluate what this means for using temperature change alone to classify a reaction. [2]
Solutions
8QuestionEnergy transfer between system and surroundingsAssessment Practice
6 marks~9 minCriterion D
Single-use hand warmers contain iron powder, water, salt, and activated carbon. When exposed to air, the iron undergoes oxidation:
The reaction releases thermal energy, raising the surface temperature of the warmer to approximately 50–60 °C. Millions of hand warmers are discarded globally each year.
The reaction releases thermal energy, raising the surface temperature of the warmer to approximately 50–60 °C. Millions of hand warmers are discarded globally each year.
a
Explain why this reaction is classified as exothermic, and describe the energy transfer that occurs between the hand warmer (system) and its surroundings. [2]
b
Explain how two different properties of the materials used in hand warmers contribute to environmental concerns when the warmers are disposed of at large scale. [2]
c
Analyse the health risk posed by the surface temperature of the hand warmer during use, and evaluate the effectiveness of one method to reduce this risk. [2]
Solutions
9QuestionEnergy profile diagrams (reactants → products)Assessment Practice
3 marks~5 minCriterion B
The table below shows activation energy () and enthalpy change () for four reactions.
| Reaction | (kJ/mol) | (kJ/mol) |
|---|---|---|
| Combustion of methane | 265 | −890 |
| Decomposition of calcium carbonate | 175 | +178 |
| Neutralisation of HCl with NaOH | 10 | −57 |
| Photosynthesis | 500 | +2800 |
a
Deduce whether each reaction is endothermic or exothermic. [1]
b
Explain how the sign of determines the classification of a reaction as endothermic or exothermic. [1]
c
Analyse the relationship between and reaction type (endothermic or exothermic) using the data provided. [1]
Solutions
10QuestionInterpreting energy diagrams (peaks, energy levels)Assessment Practice
5 marks~8 minCriterion C
An energy diagram for a reaction shows reactant energy at , product energy at , and a peak energy at . A student proposes: "Catalyst concentration inversely correlates with activation energy."
Experimental data collected at varying catalyst concentrations:
Experimental data collected at varying catalyst concentrations:
| Catalyst concentration (M) | 0.0 | 0.1 | 0.2 |
|---|---|---|---|
| Measured (kJ) | 60 | 45 | 35 |
a
Calculate the activation energy from the energy diagram. [1]
b
Deduce what the energy diagram represents in terms of the experimental conditions, using your calculated and the data table. [2]
c
Evaluate whether the experimental data supports or refutes the student's hypothesis, justifying your answer with specific values. [2]
Solutions
11QuestionEnergy profile diagrams (reactants → products)Assessment Practice
8 marks~12 minCriterion D
The catalytic decomposition of hydrogen peroxide, , has an enthalpy change of and an activation energy of . Without a catalyst, the reaction requires heating to approximately before products form at a measurable rate, despite the overall energy change being negative.
a
Explain the roles of and as shown on an energy profile diagram for this reaction. [2]
b
Apply collision theory to explain why heating to is necessary for the reaction to proceed at a measurable rate. [2]
c
Analyse the thermodynamic feasibility of this reaction and evaluate whether thermodynamic feasibility alone is sufficient to predict whether the reaction will occur under standard laboratory conditions. [4]
Solutions
12QuestionEffect of activation energy on reaction rateAssessment Practice
5 marks~8 minCriterion B
A student investigates how activation energy affects the rate of decomposition of , using five different catalysts. Oxygen gas production is measured at constant temperature.
| Reaction | A | B | C | D | E |
|---|---|---|---|---|---|
| Activation energy (kJ/mol) | 40 | 55 | 70 | 50 | 85 |
| Initial rate (mL/s) | 8.2 | 3.5 | 1.1 | 2.0 | 0.4 |
a
Deduce the relationship between activation energy and initial rate of reaction. [1]
b
Explain this relationship using collision theory. [2]
c
Identify the anomalous data point and justify why it does not fit the expected trend, using collision theory in your answer. [2]
Solutions
13QuestionBasics of Collision TheoryAssessment Practice
5 marks~8 minCriterion D
Catalytic converters use platinum and palladium to reduce the activation energy of reactions that convert toxic exhaust gases into less harmful substances. Without a catalyst, these reactions proceed too slowly at typical exhaust temperatures (approximately 300–600 °C).
a
Explain how reducing activation energy allows the conversion of and into and to proceed efficiently at exhaust temperatures. [2]
b
Explain how the catalyst provides an alternative reaction pathway to achieve this lower activation energy. [1]
c
Analyse one environmental advantage and one environmental disadvantage of catalytic converters, considering both the reduction of exhaust emissions and the extraction of platinum-group metals. [2]
Solutions
14QuestionBasics of Collision TheoryAssessment Practice
3 marks~5 minCriterion C
Two experiments investigate the effect of particle size on the rate of reaction between calcium carbonate and dilute hydrochloric acid.
Experiment 1: A 10 g lump of calcium carbonate is added to 50 cm³ of 1.0 mol dm⁻³ hydrochloric acid at 25°C.
Experiment 2: 10 g of powdered calcium carbonate is added to 50 cm³ of 1.0 mol dm⁻³ hydrochloric acid at 25°C.
The volume of carbon dioxide produced is recorded over time.
Experiment 1: A 10 g lump of calcium carbonate is added to 50 cm³ of 1.0 mol dm⁻³ hydrochloric acid at 25°C.
Experiment 2: 10 g of powdered calcium carbonate is added to 50 cm³ of 1.0 mol dm⁻³ hydrochloric acid at 25°C.
The volume of carbon dioxide produced is recorded over time.
a
Explain, using collision theory, why powdered calcium carbonate reacts faster than the lump. [2]
b
A student claims that increasing the concentration of hydrochloric acid would increase the rate more than raising the temperature by 10°C. Evaluate this claim. [1]
Solutions
15QuestionEffect of temperature on particle energy and collisionsAssessment Practice
6 marks~9 minCriterion B
A student investigates how temperature affects the rate of reaction between sodium thiosulfate solution and hydrochloric acid. A sulfur precipitate forms, making the solution turn cloudy. The student records the time for the solution to become fully opaque at five temperatures.
| Temperature (°C) | 20 | 30 | 40 | 50 | 60 |
|---|---|---|---|---|---|
| Time (s) | 120 | 60 | 30 | 15 | 7.5 |
a
Construct a graph of time (y-axis, 0–140 s) against temperature (x-axis, 20–70°C), plot all five points, and describe the pattern shown. [2]
b
Explain, using collision theory, why increasing temperature increases the rate of this reaction. [2]
c
A second student claims the reaction time at 70°C will be approximately 3.75 s. Evaluate this claim by analysing the pattern in the data and linking it to the behaviour of particles at higher temperatures. [2]
Solutions
16QuestionInterpreting rate graphs and experimental dataAssessment Practice
5 marks~8 minCriterion C
A student proposes the hypothesis: "Increasing the temperature of a chemical reaction always doubles the reaction rate." To investigate this, they measure the time for a fixed mass of solid calcium carbonate (CaCO3) and 50 cm³ of 1.0 mol dm⁻³ hydrochloric acid (HCl) to fully react at four temperatures.
| Temperature (°C) | 20 | 30 | 40 | 50 |
|---|---|---|---|---|
| Reaction time (s) | 120 | 60 | 30 | 15 |
a
Calculate the reaction rate at each temperature using rate . Show your working. [2]
b
Using your calculated rates, explain whether the data supports the hypothesis for a 10°C temperature increase. [1]
c
Evaluate the student's hypothesis as a general claim, using collision theory to justify why it is an oversimplification. [2]
Solutions
17QuestionSurface area and its role in solid reactionsAssessment Practice
2 marks~3 minCriterion D
In the Haber process, iron is used as a catalyst to produce ammonia () from nitrogen and hydrogen gases. A factory switches from iron pellets to powdered iron.
a
Explain why powdered iron increases the rate of reaction compared to iron pellets. [1]
b
A faster reaction allows the factory to maintain the same ammonia output at a lower operating temperature. Evaluate one environmental consequence of this temperature reduction. [1]
Solutions
18QuestionClosed system requirement for equilibriumAssessment Practice
7 marks~11 minCriterion B
A student investigates the equilibrium between nitrogen dioxide and dinitrogen tetroxide in a sealed syringe:
Different amounts of NO are injected and, after equilibrium is reached at constant temperature, concentrations are recorded:
Different amounts of NO are injected and, after equilibrium is reached at constant temperature, concentrations are recorded:
| Injection | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|
| (M) | 0.10 | 0.20 | 0.35 | 0.55 | 0.80 |
| (M) | 0.05 | 0.10 | 0.18 | 0.28 | 0.41 |
a
Construct a graph of (y-axis) against (x-axis) and interpret the relationship shown. [2]
b
Deduce the equilibrium concentration of NO when M. Show your method clearly. [2]
c
Analyse why does not increase in direct proportion to , using both the equilibrium expression for this reaction and collision theory. [3]
Solutions
19QuestionEffect of changes in conditions (temperature, concentration – basic idea)Assessment Practice
5 marks~8 minCriterion D
The reversible reaction between dinitrogen tetroxide and nitrogen dioxide is:
The forward reaction produces , a brown gas. A student investigates the effect of temperature on equilibrium by heating sealed tubes of the gas mixture and measuring the concentration of once equilibrium is reached. Results are shown in the graph below.
The student hypothesises that the forward reaction is exothermic.
The forward reaction produces , a brown gas. A student investigates the effect of temperature on equilibrium by heating sealed tubes of the gas mixture and measuring the concentration of once equilibrium is reached. Results are shown in the graph below.
The student hypothesises that the forward reaction is exothermic.
a
State Le Chatelier's principle as it applies to a change in temperature. [1]
b
Interpret the graph to describe how the equilibrium position changes as temperature increases. [2]
c
Evaluate the student's hypothesis using your answers to (a) and (b). [2]
Solutions
20QuestionDefinition of reversible reactionsAssessment Practice
3 marks~5 minCriterion C
The graph below shows how the forward and reverse reaction rates change over time for a closed system at constant temperature, based on the equation:
At s, the forward rate is and the reverse rate is zero. Both rates converge over approximately 20 s until they are equal and constant at , where they remain.
At s, the forward rate is and the reverse rate is zero. Both rates converge over approximately 20 s until they are equal and constant at , where they remain.
a
Justify the time at which the system first reaches equilibrium. [1]
b
Explain what the equal, constant rates after 20 s indicate about the concentrations of and in the system. [1]
c
Discuss why the forward reaction rate does not drop to zero when the system reaches equilibrium, even though there is no net change in concentration. [1]
Solutions