Chemical energetics — IGCSE Chemistry (0620) questions by topic
Classifying whether striking a match is an endothermic or exothermic reaction, comparing sodium hydrogencarbonate's reaction with hydrochloric acid against ethanoic acid, describing thermal energy transfer during an endothermic reaction, and reading reaction-pathway diagrams to spot the endothermic profile are the recurring tasks in this topic, worth 1 to 20 marks across 38 real questions from 2023 to 2025 papers.
Identify, explain, complete, calculate and state are the top command words, and explain in an energetics context means linking energy transfer direction to a temperature change in the surroundings, not just naming the reaction type. Because endothermic and exothermic reasoning is tested repeatedly with different reactions substituted in, working through a run of these and checking each against instant marking confirms the direction of energy transfer has actually been reasoned through, not guessed.
May–June 2025, Paper 11
Three statements about energy changes in chemical reactions are listed. 1 In an endothermic reaction, the temperature of the surroundings increases. 2 In an exothermic reaction,…
Answer this question and get it marked →May–June 2025, Paper 12
Which reaction pathway diagram shows the largest increase in the temperature of the surroundings? (The scale on the y-axis is the same in each diagram.) A energy of products is…
Answer this question and get it marked →May–June 2025, Paper 13
When ammonium nitrate is added to water, the temperature of the mixture decreases. The ammonium nitrate can be recovered by evaporating the water. Which statement explains these…
Answer this question and get it marked →May–June 2025, Paper 21
Water is added to anhydrous copper(II) sulfate in a test-tube. The mixture becomes hot. Which type of reaction and reaction pathway diagram apply to this reaction? Each option…
Answer this question and get it marked →May–June 2025, Paper 22
A reaction pathway diagram is shown. The diagram plots energy against progress of reaction, with the products at a higher energy than the reactants and an energy barrier (peak)…
Answer this question and get it marked →The average bond energy for the C-H bond is 413 kJ/mol. What is the enthalpy change when 1.0 mol of methane molecules is formed from carbon and hydrogen atoms? A -1652 kJ B -413…
Answer this question and get it marked →May–June 2025, Paper 23
Two statements about hydrogen are listed. 1 Hydrogen is used as a fuel. 2 When hydrogen burns in the air to form water, thermal energy is produced. Which conclusion about these…
Answer this question and get it marked →Which row describes an exothermic reaction? sign of enthalpy change, deltaH temperature of the surroundings --- --- --- A positive decreases B positive increases C negative…
Answer this question and get it marked →A reaction pathway diagram is shown. The diagram plots energy against progress of reaction. The reactants are at a higher energy level than the products. The curve rises to a peak…
Answer this question and get it marked →May–June 2025, Paper 31
This question is about energy changes in reactions. Table 7.1 shows the results of four experiments. Table 7.1 experiment initial temperature / degrees C final temperature /…
Answer this question and get it marked →May–June 2025, Paper 51
Solid sodium hydrogencarbonate, NaHCO3, reacts with dilute hydrochloric acid and with dilute ethanoic acid. NaHCO3(s) + HCl(aq) - NaCl(aq) + CO2(g) + H2O(l) NaHCO3(s) +…
Answer this question and get it marked →May–June 2025, Paper 52
You are going to investigate the temperature change when anhydrous lithium chloride dissolves in water. Read all of the instructions carefully before starting the experiments.…
Answer this question and get it marked →May–June 2025, Paper 61
Solid sodium hydrogencarbonate, NaHCO3, reacts with dilute hydrochloric acid and with dilute ethanoic acid. NaHCO3(s) + HCl(aq) - NaCl(aq) + CO2(g) + H2O(l) NaHCO3(s) +…
Answer this question and get it marked →May–June 2025, Paper 62
Use the information in the description of the experiments and the thermometer diagrams to complete Table 2.1. Table 2.1 (as given): experiment mass of anhydrous lithium chloride…
Answer this question and get it marked →May–June 2024, Paper 11
Which row describes what happens during an endothermic reaction? (columns: thermal energy is transferred; change in temperature of the reaction mixture) A from the surroundings;…
Answer this question and get it marked →Water is added to anhydrous copper(II) sulfate. Which row describes the direction of energy change and the colour change of the mixture during the reaction? (columns: direction of…
Answer this question and get it marked →May–June 2024, Paper 12
Three reactions are described: 1 An acid is added to substance H. Rapid fizzing happens and the temperature decreases. 2 When substance J is ignited, it produces large quantities…
Answer this question and get it marked →May–June 2024, Paper 13
Which statements about endothermic reactions are correct? 1 The energy of the products is greater than the energy of the reactants. 2 The energy of the reactants is greater than…
Answer this question and get it marked →May–June 2024, Paper 21
The reaction between hydrogen and oxygen releases 486 kJ/mol of energy: 2H2(g) + O2(g) → 2H2O(g) The bond energy of H-H is 436 kJ/mol and that of H-O is 464 kJ/mol. What is the…
Answer this question and get it marked →Which reaction pathway diagram (A, B, C or D) shows the reaction that will give out the most energy? The scale on the y-axis is the same in each diagram. Diagram A shows reactants…
Answer this question and get it marked →May–June 2024, Paper 22
Three statements about activation energy, Ea, are listed: 1 Colliding particles must have at least Ea before they can react. 2 Ea for exothermic reactions is always greater than…
Answer this question and get it marked →May–June 2024, Paper 23
Plant cells use energy from sunlight for photosynthesis. Which row describes and explains the energy change that occurs? (columns: type of energy change; explanation of energy…
Answer this question and get it marked →Two different experiments are done to find the enthalpy change, ΔH, of each reaction. The temperature is measured at the beginning and after 3 minutes. In experiment 1 the…
Answer this question and get it marked →The reaction pathway diagram for an endothermic reaction is shown; u, v and w are known energy values, with reactants at energy u and products at the higher energy v, and the peak…
Answer this question and get it marked →May–June 2024, Paper 61
A student investigates the temperature change when magnesium reacts with dilute sulfuric acid. The student does five experiments. Experiment 1: Pour 20 cm3 of dilute sulfuric acid…
Answer this question and get it marked →October–November 2024, Paper 11
Which reaction pathway diagram represents an endothermic reaction? (Four energy-vs-progress-of-reaction profiles are shown: A reactants higher than products; B products higher…
Answer this question and get it marked →The diagram shows a match. By striking the match, a chemical reaction takes place. Which row describes the chemical reaction? type of reaction reason --- --- --- A endothermic…
Answer this question and get it marked →October–November 2024, Paper 12
The temperature of the water in two beakers, X and Y, is measured as 21.5 °C. 5 g of sodium chloride is dissolved in the water in beaker X. The temperature changes to 18.0 °C. 5 g…
Answer this question and get it marked →October–November 2024, Paper 13
Which row describes the reaction pathway diagram and energy change in an exothermic reaction? reaction pathway diagram energy is --- --- --- A reactants higher than products…
Answer this question and get it marked →The table shows the initial and final temperatures for four different reactions. reaction initial temperature / °C final temperature / °C --- --- --- 1 19 28 2 18 16 3 20 20 4 18…
Answer this question and get it marked →October–November 2024, Paper 21
Two reaction pathway diagrams are shown, each with arrows A and B (first diagram) and C and D (second diagram) marking energy changes. Which arrow represents the activation energy…
Answer this question and get it marked →October–November 2024, Paper 22
The equation for the formation of ammonia is shown. N2 + 3H2 - 2NH3 The reaction pathway diagram shows activation energy = +250 kJ/mol from the reactants N2 + 3H2 up to the peak,…
Answer this question and get it marked →October–November 2024, Paper 23
Which reaction pathway diagram is correctly labelled? (Four energy-vs-progress diagrams A-D are shown, each labelling the activation energy Ea and the enthalpy change ΔH; the…
Answer this question and get it marked →Which row describes a reaction where the overall energy change is exothermic? energy needed for breaking bonds / kJ energy released by forming bonds / kJ temperature of the…
Answer this question and get it marked →October–November 2024, Paper 53
You are going to investigate the temperature change when solid P dissolves in water. Read all of the instructions carefully before starting the experiments. You are going to do…
Answer this question and get it marked →October–November 2024, Paper 63
A student investigates the temperature change when solid P dissolves in water. The student does two experiments. In Experiment 1, 20 cm³ of distilled water is placed in a boiling…
Answer this question and get it marked →May–June 2023, Paper 63
A student investigates the temperature change when solid citric acid reacts with solid sodium carbonate, in six experiments. Experiment 1: 5.0 g of solid sodium carbonate stirred…
Answer this question and get it marked →October–November 2023, Paper 42
Chemical reactions can involve transfer of thermal energy. State the term used for the transfer of thermal energy during a reaction.
Answer this question and get it marked →Other IGCSE Chemistry topics
- Organic chemistry (155)
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- Metals (96)
- Acids, bases and salts (84)
- Experimental techniques and chemical analysis (84)
- Chemical reactions (80)
- Stoichiometry (62)
- Chemical bonding (58)
- Chemistry of the environment (55)
- Atoms, elements and compounds (51)
- Electrochemistry (47)
- Practical skills (43)