Rates of Reaction and Energy Changes — Free IB MYP4 Chemistry Questions

1QuestionTemperature changes during reactionsConcept Practice

3 marks~5 minCriterion A

The energy profile diagram below shows the energy changes during a chemical reaction.

a

Deduce whether this reaction is endothermic or exothermic. [1]

b

Explain, in terms of bond breaking and bond forming, why this reaction has the overall energy change shown in the diagram. [2]

Solutions

2QuestionEnergy profile diagrams (reactants → products)Concept Practice

2 marks~3 minCriterion A

The energy profile diagram below shows a chemical reaction. The vertical axis represents potential energy and the horizontal axis represents progress of the reaction. A curved line rises from the reactants on the left to a peak, then falls to the products on the right. An arrow is drawn vertically from the reactants' energy level to the peak of the curve.

a

Identify what the arrow in the diagram represents. [1]

b

Explain why this quantity is essential for the forward reaction to occur. [1]

Solutions

3QuestionDefinition of activation energyConcept Practice

3 marks~5 minCriterion A

The reaction coordinate diagram below shows two curves for the same reaction: an uncatalyzed pathway (solid curve) with activation energy

120 \text{ kJ mol}^{-1}

and a catalyzed pathway (dashed curve) with activation energy

75 \text{ kJ mol}^{-1}

.

a

Define activation energy. [1]

b

Identify which pathway produces a faster reaction rate and justify your answer by comparing the two activation energy values. [1]

c

Using collision theory, explain how the lower activation energy of the catalyzed pathway results in a greater proportion of successful collisions at the same temperature. [1]

Solutions

4QuestionSurface area and its role in solid reactionsConcept Practice

3 marks~5 minCriterion A

A student adds a large marble chip of calcium carbonate (

CaCO_3(s)

) to a beaker of dilute hydrochloric acid (

HCl(aq)

). In a separate beaker, the same mass of powdered calcium carbonate is added to an equal volume and concentration of hydrochloric acid. The powdered form reacts significantly faster.

a

Construct the balanced chemical equation, including state symbols, for the reaction between calcium carbonate and hydrochloric acid. [1]

b

Explain, using collision theory, why the powdered calcium carbonate reacts faster than the marble chip. [2]

Solutions

5QuestionEffect of changes in conditions (temperature, concentration – basic idea)Concept Practice

2 marks~3 minCriterion A

The Haber process produces ammonia via the following reversible reaction:

\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)

a

Explain what the symbol

\rightleftharpoons

indicates about this reaction, referring to the forward reaction and the reverse reaction. Use the state symbols in your answer. [1]

b

Explain what is meant by the term equilibrium in the context of this reaction. [1]

Solutions

6QuestionIdentifying reaction type from descriptions or dataAssessment Practice

3 marks~5 minCriterion C

A student dissolves two different salts separately in water inside insulated cups and records the temperature of the solution every 30 seconds.

The graph shows the results.

Reaction A: temperature rises steadily from 20 °C to 34 °C over 3 minutes.
Reaction B: temperature falls steadily from 20 °C to 11 °C over 3 minutes.

a

Identify the reaction type (endothermic or exothermic) for each reaction. [1]

b

Explain the temperature change observed in Reaction A in terms of energy transfer between the reaction and its surroundings. [1]

c

The student claims that Reaction B "destroys energy" because the surroundings lose heat. Evaluate this claim. [1]

Solutions

7QuestionTemperature 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 (

\Delta T

) for each:

Metal	magnesium	zinc	iron	copper	silver
$\Delta T$ (°C)	+24.5	+12.0	+5.5	0.0	0.0

An unknown metal X, tested under identical conditions, gives

\Delta T = +8.5

°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

\Delta T

, referring to at least three metals in your answer. [2]

c

Deduce the identity of metal X. Justify your answer using both the

\Delta T

data and the reactivity series. [2]

Solutions

8QuestionIdentifying reaction type from descriptions or dataAssessment Practice

6 marks~9 minCriterion D

Self-heating meal pouches, used by hikers and military personnel, contain a compartment of magnesium metal. When water is added, the following reaction occurs:

\text{Mg}(s) + 2\text{H}_2\text{O}(l) \rightarrow \text{Mg(OH)}_2(s) + \text{H}_2(g)

The reaction releases sufficient heat to warm a meal without any external flame or electricity. Magnesium hydroxide accumulates as a solid residue, and hydrogen gas is released into the surroundings.

a

Deduce whether this reaction is endothermic or exothermic. Justify your answer using evidence from the information above. [1]

b

Explain one societal benefit of this technology for people in remote or emergency situations. [2]

c

Evaluate one environmental limitation of this technology, considering the reaction products and their disposal, and discuss how this limitation affects the overall effectiveness of the technology. [3]

Solutions

9QuestionActivation energy and overall energy change (ΔH – qualitative)Assessment Practice

3 marks~5 minCriterion B

The table below shows activation energy (

E_a

) and overall energy change (

\Delta H

) for four reactions.

Reaction	$E_a$ (kJ mol $^{-1}$ )	$\Delta H$ (kJ mol $^{-1}$ )
Combustion of methane	265	−890
Decomposition of hydrogen peroxide	75	−98
Rusting of iron	165	−1640
Photosynthesis	light-driven	+2800

a

Deduce the relationship between

E_a

and whether a reaction is exothermic or endothermic, using the data to support your answer. [1]

b

Explain how the relative energy levels of reactants and products differ between exothermic and endothermic reactions. [1]

c

Photosynthesis has a positive

\Delta H

yet requires light rather than a conventional activation energy. Analyse what this suggests about the role of

E_a

in determining the energy stored in the products of a reaction. [1]

Solutions

10QuestionEnergy profile diagrams (reactants → products)Assessment Practice

5 marks~8 minCriterion D

The Haber-Bosch process synthesises ammonia at 400–500°C and 200 atm, consuming large quantities of fossil fuel energy. A low-temperature alternative operates at 150°C and 10 atm using a toxic catalyst. The energy profile diagram shows two curves (A: Haber-Bosch; B: catalytic) starting at the same reactant energy level and ending at the same product energy level, with Curve A reaching a significantly higher peak than Curve B.

a

On the energy profile diagram, label the activation energy

E_a

for each process. [1]

b

Analyse how the energy profiles of the two processes account for the difference in their environmental carbon footprints. [2]

c

Evaluate the trade-offs between the environmental benefit and the health and safety risks introduced by using the toxic catalyst in the low-temperature process. [2]

Solutions

11QuestionInterpreting energy diagrams (peaks, energy levels)Assessment Practice

3 marks~5 minCriterion C

Disposable hand warmers use the oxidation of iron:

4\text{Fe} + 3\text{O}_2 \rightarrow 2\text{Fe}_2\text{O}_3

. The energy profile for this reaction is shown below.

a

Interpret the energy profile to explain why the hand warmer releases heat to the user's hands. [2]

b

A student claims that used hand warmers can simply be thrown in general waste without environmental consequence. Evaluate this claim, referring to one specific environmental impact of disposal. [1]

Solutions

12QuestionDefinition of activation energyAssessment Practice

4 marks~6 minCriterion D

Nitrogen monoxide (

\text{NO}

) forms in car engines when

\text{N}_2

and

\text{O}_2

react at temperatures above

1500\ °\text{C}

. This reaction has an activation energy of approximately

500\ \text{kJ mol}^{-1}

, far higher than most reactions occurring at Earth's surface. Once released,

\text{NO}

contributes to serious atmospheric problems. Catalytic converters are fitted to vehicles to promote the decomposition reaction

2\text{NO} \rightarrow \text{N}_2 + \text{O}_2

.

a

Explain why the reaction between

\text{N}_2

and

\text{O}_2

does not occur at Earth's surface temperatures. [1]

b

Explain how temperatures above

1500\ °\text{C}

inside a car engine allow this reaction to proceed. [1]

c

Analyse the health and environmental impacts of

\text{NO}

emissions, and evaluate the effectiveness of catalytic converters in reducing these impacts. [2]

Solutions

13QuestionGraphical interpretation (energy distribution concept – qualitative)Assessment Practice

7 marks~11 minCriterion C

A student investigates the rate of reaction between substance X and hydrochloric acid at five temperatures. The results are:

Temperature (°C)	20	30	40	50	60
Initial rate (mol dm $^{-3}$ s $^{-1}$ )	0.002	0.005	0.012	0.028	0.065

Four Maxwell–Boltzmann energy distribution curves (A, B, C, D) for this reaction are shown in the diagram. Curve A has the highest, narrowest peak; curve D has the lowest, broadest peak; curves B and C are intermediate. A vertical line marks

E_a

on the energy axis.

Possible identities for substance X, with

E_a

for reaction with hydrochloric acid:

Substance	Zinc	Magnesium	Calcium	Iron
$E_a$ (kJ mol $^{-1}$ )	54	42	30	68

a

Deduce which curve corresponds to 20°C and which corresponds to 60°C. [2]

b

The rate increases from 0.002 to 0.065 mol dm

^{-3}

s

^{-1}

as temperature rises from 20°C to 60°C. Using collision theory, explain what the curves reveal about the fraction of molecules exceeding

E_a

at these two temperatures. [2]

c

Using the rate data and your answer to (b), evaluate which substance is most likely to be X. Justify your reasoning. [3]

Solutions

14QuestionEffect of activation energy on reaction rateAssessment Practice

5 marks~8 minCriterion B

A student investigates how activation energy affects the rate of decomposition of

\text{H}_2\text{O}_2\text{(aq)}

, 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

15QuestionEffect of temperature on particle energy and collisionsAssessment Practice

5 marks~8 minCriterion C

A student investigates the effect of temperature on the reaction between sodium thiosulfate solution and hydrochloric acid, measuring the time for the solution to turn opaque.

Temperature (°C)	10	20	30	40	50
Reaction time (s)	120	60	30	15	7.5
Mean kinetic energy (kJ mol $^{-1}$ )	3.5	3.6	3.7	3.8	3.9

The student hypothesises: "The reaction rate doubles every 10°C because particles move twice as fast."

a

Calculate the reaction rate at 10°C and at 50°C, and deduce the overall rate increase across this temperature range. [1]

b

Using the kinetic energy data, show that particle speed does not double between 10°C and 20°C, given that

KE \propto v^2

. [2]

c

Evaluate the student's hypothesis, explaining the actual cause of the observed rate increase using collision theory and the Maxwell-Boltzmann distribution. [2]

Solutions

16QuestionEffect of temperature on particle energy and collisionsAssessment Practice

6 marks~9 minCriterion D

Food spoilage is accelerated by microbial and enzymatic activity. Refrigerators typically maintain an internal temperature of around 4 °C, compared with a room temperature of approximately 22 °C.

a

Explain how lowering the temperature from 22 °C to 4 °C reduces the rate of food spoilage reactions, with reference to particle energy and collision frequency. [2]

b

Analyse the health risks that arise when perishable food is left at room temperature for several hours, linking your answer to reaction rate principles. [2]

c

Evaluate the limitations of refrigeration as a universal food preservation strategy, considering at least two distinct factors. [2]

Solutions

17QuestionEffect 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

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:

2\,\text{NO}_2\text{(g)} \rightleftharpoons \text{N}_2\text{O}_4\text{(g)} \quad \Delta H = -58 \text{ kJ mol}^{-1}

Different amounts of NO

_2

are injected and, after equilibrium is reached at constant temperature, concentrations are recorded:

Injection	1	2	3	4	5
$[\text{NO}_2]_{eq}$ (M)	0.10	0.20	0.35	0.55	0.80
$[\text{N}_2\text{O}_4]_{eq}$ (M)	0.05	0.10	0.18	0.28	0.41

a

Construct a graph of

[\text{N}_2\text{O}_4]_{eq}

(y-axis) against

[\text{NO}_2]_{eq}

(x-axis) and interpret the relationship shown. [2]

b

Deduce the equilibrium concentration of N

_2

O

_4

when

[\text{NO}_2]_{eq} = 1.00

M. Show your method clearly. [2]

c

Analyse why

[\text{N}_2\text{O}_4]_{eq}

does not increase in direct proportion to

[\text{NO}_2]_{eq}

, using both the equilibrium expression for this reaction and collision theory. [3]

Solutions

19QuestionClosed system requirement for equilibriumAssessment Practice

10 marks~15 minCriterion D

The Haber–Bosch process produces ammonia (

\text{NH}_3

) for synthetic fertilizers in a closed system at approximately 200 atm and 450°C using an iron catalyst:

\text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightleftharpoons 2\text{NH}_3\text{(g)} \quad \Delta H = -92 \text{ kJ mol}^{-1}

Hydrogen is sourced from natural gas via steam methane reforming, releasing approximately 1.9 tonnes of

\text{CO}_2

per tonne of

\text{NH}_3

produced. The process currently supports food production for roughly half the world's population.

a

Explain why a closed system is necessary for equilibrium to be established, and explain how operating at 200 atm increases the yield of

\text{NH}_3

. [3]

b

Discuss the relationship between the Haber–Bosch process and global food security, referring to both the scale and the mechanism of its contribution. [3]

c

Evaluate the environmental impact of the Haber–Bosch process, considering both energy consumption and

\text{CO}_2

emissions, and assess whether the societal benefits justify continuing the process in its current form. [4]

Solutions

20QuestionDefinition of reversible reactionsAssessment Practice

4 marks~6 minCriterion C

When blue hydrated copper(II) sulfate crystals,

CuSO_4 \cdot 5H_2O

, are heated, they decompose to form white anhydrous copper(II) sulfate,

CuSO_4

, and water vapour. When water is added to the white powder, the blue colour is restored.

The diagram shows both a forward arrow (heating) and a reverse arrow (adding water) between the two forms.

a

Explain why the copper(II) sulfate reaction shown in the diagram is described as reversible. [2]

b

A student claims that heating alone is sufficient to determine the direction of any reversible reaction. Using the copper(II) sulfate system, explain why this claim is incorrect. [2]

Solutions

Rates of Reaction and Energy Changes — Free MYP4 Chemistry Practice Questions