O Level / IGCSE Chemistry chapter 5: Chemical energetics MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
24 exam-style questions on Chemical energetics, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. Which change is endothermic?
A
adding water to anhydrous copper(II) sulfate
B
burning magnesium in air
C
heating calcium carbonate to form calcium oxide and carbon dioxide
D
neutralising sodium hydroxide with hydrochloric acid
Show answer
Answer: C. Thermal decomposition takes in energy, so calcium carbonate must be heated strongly to keep it decomposing. Hydrating copper(II) sulfate, burning and neutralisation all give out thermal energy.
2. The enthalpy change for the burning of hydrogen is −286 kJ/mol. Which statement is correct?
A
the reaction is endothermic, because ΔH has a value
B
the products have more energy than the reactants
C
the surroundings cool down as the hydrogen burns
D
the reaction is exothermic, and the products have less energy than the reactants
Show answer
Answer: D. A negative ΔH means energy is transferred from the reacting chemicals to the surroundings, so the products end up with less energy and the surroundings warm up.
3. Bond energies: H–H 436 kJ/mol, Cl–Cl 242 kJ/mol, H–Cl 431 kJ/mol. What is the energy change for H2 + Cl2 → 2HCl?
neutralising an acid with an alkali, which makes the mixture warmer
B
dissolving ammonium nitrate in water, which makes the solution colder
C
burning methane in a Bunsen burner, which heats the surrounding air
D
iron rusting slowly in damp air, which makes the metal warmer
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Answer: B. A fall in temperature shows energy being taken in from the surroundings: endothermic. Combustion, neutralisation and rusting all give out energy.
5. Why is bond breaking endothermic?
A
bonds can only break when the pressure is raised very high
B
the surroundings gain heat when atoms separate from each other
C
energy is released as the attraction between the atoms is lost
D
energy has to be supplied to pull the bonded atoms apart from each other
Show answer
Answer: D. Pulling bonded atoms apart works against the attraction holding them together, so energy has to be put in.
6. Magnesium ribbon is added to dilute hydrochloric acid in a beaker. The temperature of the solution rises from 20 °C to 32 °C. Which statement is correct?
A
the reaction takes in thermal energy from the solution
B
the reaction is endothermic because the temperature changes
C
energy is destroyed in the reaction
D
the reaction is exothermic and transfers thermal energy to the surroundings
Show answer
Answer: D. A rise in temperature of the surroundings (the solution and beaker) shows that the reaction has given out thermal energy, so it is exothermic. Energy is transferred, not destroyed.
7. The thermal decomposition CaCO3 → CaO + CO2 has ΔH = +178 kJ/mol. What is the enthalpy change when 2 mol of calcium oxide react completely with carbon dioxide to form calcium carbonate?
A
−356 kJ
B
−178 kJ
C
+178 kJ
D
+356 kJ
Show answer
Answer: A. The reverse reaction has the same size of ΔH with the opposite sign, −178 kJ per mole, and for 2 mol it is 2 × −178 = −356 kJ. +356 kJ keeps the wrong sign; −178 kJ forgets the 2 mol.
8. On an energy level diagram for an endothermic reaction, the products are drawn
A
at the same level as the reactants
B
at zero energy
C
below the reactants
D
above the reactants
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Answer: D. Energy is absorbed, so the products hold more energy than the reactants and sit higher on the diagram; ΔH is positive.
9. In an exothermic reaction
A
energy is given out and the enthalpy change is negative
B
the products contain more energy than the reactants do
C
the temperature of the surroundings falls as energy is taken in
D
energy is absorbed from the surroundings and the enthalpy change is positive
Show answer
Answer: A. Exothermic reactions release energy, so the surroundings warm up and ΔH is negative (products lower in energy).
10. H2 + Br2 → 2HBr, ΔH = −103 kJ/mol. Bond energies in kJ/mol: H–H 436, Br–Br 193. What is the H–Br bond energy?
A
263 kJ/mol
B
366 kJ/mol
C
526 kJ/mol
D
732 kJ/mol
Show answer
Answer: B. Bonds broken = 436 + 193 = 629 kJ. ΔH = broken − made, so made = 629 + 103 = 732 kJ for two H–Br bonds, and 732 ÷ 2 = 366 kJ/mol. 263 comes from subtracting 103 instead of adding it.
24, each with the answer and a short explanation, across 1 topics: Exothermic and endothermic reactions. Every chapter test draws ten of them, so you can take it many times.
Is the O Level / IGCSE Chemistry chapter 5 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
