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IB Chemistry — Reactivity flashcards

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Reactivity 1–3 of the IB Chemistry course: enthalpy changes, energy cycles, fuels and entropy; stoichiometry, kinetics and equilibrium; and proton transfer, electron transfer, radical and nucleophile–electrophile mechanisms. HL content is tagged HL.

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Learn deck · part of IB Chemistry · written against: IB Diploma Programme IB Chemistry subject guide for first assessment 2025 (Structure and Reactivity); SL and HL in one deck, HL-only cards under subtopic tags starting HL. Updated 2026-10-10.

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  1. In an exothermic reaction, are the products more or less stable than the reactants, and what is the sign of ΔH?
    The products are more stable (lower enthalpy) because energy has been released to the surroundings, so ΔH is negative.
    What Drives Reactions › Enthalpy Changes and Cycles
  2. Which equation gives the heat absorbed by water in a calorimetry experiment, and what are its units?
    Q=mcΔTQ = mc\Delta T⁠, with m in g, c = 4.18 J g⁻¹ K⁻¹ for water and ΔT in K (or °C), giving Q in joules.
    What Drives Reactions › Enthalpy Changes and Cycles
  3. 50.0 cm³ of 1.00 mol dm⁻³ HCl is mixed with 50.0 cm³ of 1.00 mol dm⁻³ NaOH and the temperature rises by 6.8 °C. What is the enthalpy change of neutralisation?
    Q = 100 g × 4.18 × 6.8 = 2840 J for 0.0500 mol of water formed, so ΔH = −2.84 kJ ÷ 0.0500 mol = −56.8 kJ mol⁻¹, or −57 kJ mol⁻¹ to the 2 significant figures of ΔT.
    What Drives Reactions › Enthalpy Changes and Cycles
  4. Why is the enthalpy of combustion of ethanol measured with a spirit burner and a copper can usually much less exothermic than the data-booklet value?
    Much heat is lost to the surroundings rather than the water, combustion may be incomplete (soot forms), and some ethanol evaporates from the wick.
    What Drives Reactions › Enthalpy Changes and Cycles
  5. What is the atom economy for making hydrogen by CH₄ + H₂O → CO + 3 H₂?
    Atom economy = mass of desired product ÷ total mass of reactants × 100 = 6.06 ÷ (16.05 + 18.02) × 100 ≈ 17.8 %.
    How Much How Fast How Far › Amount of Change
  6. 10.0 g of magnesium is added to 0.500 mol of HCl (Mg + 2 HCl → MgCl₂ + H₂). Which reactant is limiting?
    Mg: 10.0 ÷ 24.31 = 0.411 mol, which would need 0.823 mol HCl. Only 0.500 mol is present, so HCl is limiting and magnesium is in excess.
    How Much How Fast How Far › Amount of Change
  7. What volume of CO₂, measured at STP, forms when 10.0 g of calcium carbonate decomposes completely?
    n(CaCO₃) = 10.0 ÷ 100.09 = 0.0999 mol = n(CO₂); V = 0.0999 × 22.7 dm³ mol⁻¹ = 2.27 dm³.
    How Much How Fast How Far › Amount of Change
  8. What is a Brønsted–Lowry acid, and what is the conjugate base of HSO₄⁻?
    A proton (H⁺) donor. When HSO₄⁻ donates a proton it becomes SO₄²⁻, its conjugate base.
    Reaction Mechanisms › Proton Transfer
  9. What does it mean to say water is amphiprotic? Name another amphiprotic species.
    Water can both donate and accept a proton (forming OH⁻ or H₃O⁺). The hydrogencarbonate ion, HCO₃⁻, can also do both.
    Reaction Mechanisms › Proton Transfer
  10. What is the value of Kw at 298 K, and what is [H⁺] in pure water at that temperature?
    Kw = [H⁺][OH⁻] = 1.00 × 10⁻¹⁴; in pure water [H⁺] = [OH⁻], so [H⁺] = 1.00 × 10⁻⁷ mol dm⁻³ (pH 7.00).
    Reaction Mechanisms › Proton Transfer

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About these cards

Review status: Second-reader reviewed, with corrections applied.

Checked against:

  • IB Diploma Programme subject guide (topic outline only; no text copied)
  • Tag order follows the IB Diploma Programme Chemistry guide for first assessment 2025 (Reactivity 1–3).
  • OpenStax Chemistry 2e, consulted as a reference; no text copied.

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