Enthalpy Calculations Worksheet

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📚 Part 1: Enthalpy calculation problems

Read each reaction and the given ΔH value. Show your working in the maths box and give a clear final answer. Note: negative ΔH = energy released (exothermic); positive ΔH = energy absorbed (endothermic).

1. Hydrogen combustion (calculate number of moles)

H₂(g) + 1/2 O₂(g) → H₂O(l) ; ΔH = -286 kJ per mole H₂O formed.

If 1430 kJ of heat is released, how many moles of H₂O are produced?

2. Methane combustion (calculate energy released)

CH₄(g) + 2 O₂(g) → CO₂(g) + 2 H₂O(l) ; ΔH = -890 kJ per mole CH₄ combusted.

If 10.0 g of CH₄ is burned, calculate the energy released. (Molar mass CH₄ = 16.04 g mol⁻¹)

3. Thermal decomposition of calcium carbonate (calculate energy absorbed)

CaCO₃(s) → CaO(s) + CO₂(g) ; ΔH = +178 kJ per mole CaCO₃ decomposed.

If 50.0 g of CaCO₃ is decomposed, how much energy is absorbed? (Molar mass CaCO₃ = 100.09 g mol⁻¹)

4. Formation of sodium chloride (calculate energy released per mole)

2 Na(s) + Cl₂(g) → 2 NaCl(s) ; ΔH = -821 kJ for the reaction as written (for 2 mol NaCl formed).

Calculate the energy released per mole of Na reacted (state sign for release).

5. Combustion of carbon (calculate mass of reactant)

C(s) + O₂(g) → CO₂(g) ; ΔH = -394 kJ per mole C burned.

If 1576 kJ of heat is released, what mass of carbon reacted? (Atomic mass C = 12.01 g mol⁻¹)

✏️ Part 2: Success criteria, differentiation & dyslexia-friendly options

Success criteria

By the end of this worksheet you should be able to:

• Identify whether ΔH values indicate energy released or absorbed and use the sign correctly.

• Convert mass ↔ moles using molar mass and use stoichiometry with ΔH to find energy or mass as required.

• Show clear working and state final answers with correct units (mol, g, kJ, kJ mol⁻¹).

Differentiation strategies

Support: Provide a periodic table and a worked example (one-to-one teacher or paired work). Allow calculator use and give intermediate steps (e.g. write moles = mass ÷ M).

Stretch: Ask students to convert kJ to J and present energy per gram as an extension, or change reaction stoichiometry for multi-step calculations.

Dyslexia-friendly reading options

• Break tasks into short lines and highlight key numbers and units in bold.

• Read problems aloud or use text-to-speech and provide printed copies with increased spacing.

• Use a coloured overlay or change font size for students who request it.

Self-assessment

Tick when you can do each task:

I can convert mass and moles correctly.

I can use ΔH to calculate energy and interpret the sign.

I can show full working and give units with my answers.

If you need help, note one thing to ask your teacher: