A Level Chemistry (A2) chapter 1: Chemical energetics MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

96 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.

96 questions · 4 topics · 10 per test

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What chapter 1 covers

Ten Chemical energetics questions with answers

Try each one, then open the answer. These ten stay the same; the test draws new ones every time.

1. Which equation represents the lattice energy of magnesium chloride?

  1. A
    MgCl2(s) → Mg2+(g) + 2Cl−(g)
  2. B
    Mg(s) + Cl2(g) → MgCl2(s)
  3. C
    Mg2+(g) + 2Cl−(g) → MgCl2(s)
  4. D
    Mg2+(aq) + 2Cl−(aq) → MgCl2(s)
Show answer

Answer: C. Lattice energy is the enthalpy change when one mole of an ionic solid is formed from its gaseous ions, so it is exothermic. The reverse change is lattice dissociation, and forming the solid from its elements is the enthalpy change of formation.

2. Which expression gives the enthalpy change of solution of barium fluoride, BaF2?

  1. A
    ΔHhyd(Ba2+) + ΔHhyd(F−) − ΔHlatt(BaF2)
  2. B
    ΔHlatt(BaF2) − ΔHhyd(Ba2+) − 2ΔHhyd(F−)
  3. C
    ΔHhyd(Ba2+) + 2ΔHhyd(F−) − ΔHlatt(BaF2)
  4. D
    ΔHhyd(Ba2+) + 2ΔHhyd(F−) + ΔHlatt(BaF2)
Show answer

Answer: C. Route: solid → gaseous ions (−ΔHlatt) → aqueous ions (sum of hydration enthalpies). There are two F− ions per formula unit, so the fluoride term is doubled; adding ΔHlatt forgets that the lattice is being broken up.

3. The distance between the centres of neighbouring ions is similar in NaF and in MgO. Why is the lattice energy of MgO about four times as exothermic as that of NaF?

  1. A
    the O2− ion is much smaller than the F− ion, so it attracts Mg2+ more strongly
  2. B
    the MgO lattice has a higher coordination number than the NaF lattice
  3. C
    more energy is released when an oxygen atom gains two electrons than when fluorine gains one
  4. D
    the product of the ionic charges is four times larger, so the ions attract more strongly
Show answer

Answer: D. The strength of the attraction depends on the product of the ionic charges divided by the distance between the ions. With similar distances, (2+)(2−) is four times (1+)(1−). O2− is in fact slightly larger than F−. Electron affinities are separate steps of the cycle, not part of the lattice energy.

4. Why is the enthalpy change of hydration of every ion negative?

  1. A
    Hydrogen bonds between water molecules are broken.
  2. B
    Covalent bonds form between the ion and oxygen atoms of water.
  3. C
    The ionic bonds in the solid lattice are broken.
  4. D
    Ion–dipole attractions form between the ion and polar water molecules.
Show answer

Answer: D. Gaseous ions attract the δ− or δ+ ends of water molecules, and forming these ion–dipole attractions releases energy. Breaking the lattice is not part of hydration because the ions start as a gas.

5. Hydrogen peroxide decomposes: 2H2O2(l) → 2H2O(l) + O2(g), ΔH⦵ = −196 kJ mol−1. How does temperature affect the feasibility of this reaction?

  1. A
    It is feasible only at low temperatures, because ΔH is negative.
  2. B
    It is feasible at all temperatures, because ΔH is negative and ΔS is positive.
  3. C
    It is feasible only at high temperatures, because ΔS is positive.
  4. D
    It is not feasible at any temperature, because a gas is formed.
Show answer

Answer: B. One mole of gas is formed from liquids, so ΔS is positive. With ΔH negative and −TΔS negative, ΔG is negative at every temperature. Feasibility does not mean the reaction is fast; it is slow without a catalyst.

6. Which statement about the standard enthalpy change of hydration of an ion is correct?

  1. A
    It refers to one mole of a solid ionic compound dissolving in water, and it can be exothermic or endothermic.
  2. B
    It refers to one mole of gaseous ions dissolving in water, and it is endothermic for negative ions.
  3. C
    It refers to one mole of gaseous ions dissolving in water to form a very dilute solution, and it is always exothermic.
  4. D
    It refers to one mole of water molecules bonding to ions, and it is always endothermic.
Show answer

Answer: C. Hydration starts from gaseous ions, e.g. Na+(g) + aq → Na+(aq), and new ion–water attractions form, so it is always exothermic for cations and anions alike. Dissolving the solid is the enthalpy change of solution.

7. For which reaction is the entropy change of the system most positive?

  1. A
    2NaHCO3(s) → Na2CO3(s) + H2O(g) + CO2(g)
  2. B
    CaCO3(s) → CaO(s) + CO2(g)
  3. C
    H2(g) + Cl2(g) → 2HCl(g)
  4. D
    2C2H6(g) + 7O2(g) → 4CO2(g) + 6H2O(l)
Show answer

Answer: A. The biggest entropy increase comes from the biggest increase in the number of moles of gas. Sodium hydrogencarbonate gives two moles of gas from solids, calcium carbonate gives one, H2 + Cl2 gives no change, and burning ethane turns nine moles of gas into four.

8. Which equation represents the standard enthalpy change of atomisation of bromine?

  1. A
    ½Br2(l) → Br(g)
  2. B
    ½Br2(g) → Br(g)
  3. C
    Br2(l) → 2Br(g)
  4. D
    Br2(g) → 2Br(g)
Show answer

Answer: A. Atomisation forms one mole of gaseous atoms from the element in its standard state, and bromine is a liquid at 298 K. Br2(g) → 2Br(g) forms two moles of atoms from the gas: that is the Br−Br bond energy.

9. The Cl−Cl bond energy is +242 kJ mol−1. What is the standard enthalpy change of atomisation of chlorine?

  1. A
    +60 kJ mol−1
  2. B
    +121 kJ mol−1
  3. C
    +242 kJ mol−1
  4. D
    +484 kJ mol−1
Show answer

Answer: B. Atomisation forms one mole of Cl(g): ½Cl2(g) → Cl(g), so ΔHat = ½ × 242 = +121 kJ mol−1. The bond energy itself breaks one mole of Cl2 into two moles of atoms.

10. For MgCO3(s) → MgO(s) + CO2(g), ΔH⦵ = +117 kJ mol−1 and ΔS⦵ = +175 J K−1 mol−1. What is the minimum temperature at which this decomposition is feasible?

  1. A
    669 K
  2. B
    0.669 K
  3. C
    396 K
  4. D
    942 K
Show answer

Answer: A. The reaction just becomes feasible when ΔG = 0, so T = ΔH/ΔS = 117 000 J mol−1 ÷ 175 J K−1 mol−1 = 669 K. Forgetting to convert kJ to J gives 0.669 K; 396 and 942 come from wrongly subtracting or adding 273.

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Chemical energetics: questions students ask

How many Chemical energetics MCQs are there?

96, each with the answer and a short explanation, across 4 topics: Lattice energy and Born-Haber cycles, Enthalpies of solution and hydration, Entropy change, ΔS, Gibbs free energy change, ΔG. Every chapter test draws ten of them, so you can take it many times.

Is the A Level Chemistry (A2) chapter 1 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.

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