Bonding, structure, properties and energy changes

Practice

Recall it first, then use it — testing yourself builds the memory, where rereading the notes above only feels easier.

Recall and application shuffled together — you have to work out what each item wants before you can answer it, which is the part the exam actually tests. Both kinds feed the same spacing schedule, so anything you miss comes back sooner.

Say the answer out loud before flipping — that attempt is where the learning happens, even when you get it wrong.

Exam-style only. Instant feedback, shuffled each attempt, best score saved on this device.

What actually comes up

Three questions every year, in a stable order: bonding/energy calculations mixed with a structure-and-melting-point explanation (Q1), polarity and solubility (Q2), and Lewis structures plus a second round of energy calculations, often ending in a conductivity or property comparison (Q3). "Explain" and "justify" parts always want structure AND bonding named explicitly, then linked to the observed property — never the property stated alone.

Across 4 years

The pattern — what to prepare

The 2025 paper ↗ Marking schedule ↗

Question One

NaCl reacts with AgNO₃; a melting-point table compares four solid types; diamond and gold are compared; the Haber-Bosch process forms ammonia.

• 73.0 g NaCl releases 81.8 kJ; M(NaCl) = 58.4 g mol⁻¹
• N₂ + 3H₂ → 2NH₃, ΔrH = −93.0 kJ mol⁻¹; H–H 436, N–H 391 kJ mol⁻¹

• a Calculate the ΔrH for the reaction per mole, given 73.0 g of NaCl releases 81.8 kJ. Achieved
• b Match zinc, ammonia, diamond and sodium chloride to a melting-point table, then relate the bonding and structure of ionic and molecular solids to their relative melting points. Excellence
• c Explain how the structure and bonding of diamond and gold each result in their observed hardness/malleability. Excellence
• d Calculate the average bond energy of the N≡N bond in N₂, given the reaction's ΔrH and the H–H and N–H bond energies. Excellence

Question Two

Endo/exo classification, an ammonium nitrate energy diagram, three compounds with polar bonds (methanol, tetrachloromethane, water), and solubility predictions.

• NH₄NO₃(s) → NH₄⁺(aq) + NO₃⁻(aq), shown on an energy diagram

• a Classify three statements as endothermic or exothermic, then classify the enthalpy diagram for water condensing, and for the NH₄NO₃ dissolving reaction shown. Merit
• b Define what makes a bond polar with an example, identify the non-polar molecule among methanol, tetrachloromethane and water, and justify the choice. Excellence
• c Predict the solubility of tetrachloromethane in water, magnesium bromide in hexane, and bromine in hexane. Merit
• d Explain what makes NaCl soluble in water but iodine insoluble, referring to structure, bonding, and interaction with water, with a diagram of NaCl dissolving. Excellence

Question Three

Diamond vs graphite conductivity, ethanol combustion energy calculations, Lewis structures for CO₂/Cl₂O/BF₃, and a methane-vs-ammonia shape comparison.

• C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O, ΔrH = −1370 kJ mol⁻¹; M(C₂H₅OH) = 46.7 g mol⁻¹
• 2Zn + O₂ → 2ZnO, ΔrH = −696 kJ mol⁻¹; M(ZnO) = 81.4 g mol⁻¹

• a Compare and contrast the structure and bonding of diamond and graphite, define electrical conductivity, and justify the difference in conductivity. Excellence
• b Calculate the mass of ethanol needed to release 17 500 kJ, and the energy change when 187 g of ZnO is produced. Excellence
• c Draw the Lewis structure and name the shape of CO₂, Cl₂O, and BF₃. Achieved
• d Compare the shapes of methane and ammonia, explaining the factors that determine the arrangement around the central atom and the final molecular shape. Excellence

The 2024 paper ↗ Marking schedule ↗

Question One

Lewis structures for NI₃, H₂S and CS₂; SiH₄ vs HNO shape comparison; H₂S vs HCN polarity; methanamine formed from hydrogen cyanide.

• HCN + 2H₂ → CH₃NH₂, ΔrH = −158 kJ mol⁻¹; M(CH₃NH₂) = 31.0 g mol⁻¹

• a Draw the Lewis structure for two given molecules and name their shapes. Achieved
• b Compare and contrast the shapes and bond angles of SiH₄ and HNO. Excellence
• c Identify the shared polarity of H₂S and HCN, and justify it by linking bonding/structure to how molecular polarity is determined. Excellence
• d Calculate the mass of methanamine formed when 1890 kJ is released, then choose and label the correct energy diagram. Excellence

Question Two

A melting-point/bonding table for SiO₂, SiCl₄, CuCl₂ and Al; a SiO₂ vs SiCl₄ melting-point comparison; solubility of SiCl₄ vs CuCl₂ in water.

• a Complete a table of melting point, solid type, particle type, and attractive forces for SiO₂, SiCl₄, CuCl₂ and Al. Merit
• b Explain why SiCl₄ has a considerably lower melting point than SiO₂, despite both containing silicon. Excellence
• c Explain why SiCl₄ does not dissolve in water but CuCl₂ does, naming a solvent SiCl₄ would dissolve in and including a diagram for CuCl₂. Excellence

Question Three

Propane vs butane combustion energy per kg; a hydrogen fuel cell bond-energy calculation; "Galvorn" carbon and aluminium conductivity/malleability.

• C₃H₈ + 5O₂ → 3CO₂ + 4H₂O, ΔrH = −2044 kJ mol⁻¹, M = 44.1 g mol⁻¹
• 2C₄H₁₀ + 13O₂ → 8CO₂ + 10H₂O, ΔrH = −2877 kJ mol⁻¹, M = 58.1 g mol⁻¹
• 2H₂ + O₂ → 2H₂O, ΔrH = −484 kJ mol⁻¹; H–H 436, O=O 498 kJ mol⁻¹

• a Calculate the energy released per 1.00 kg of propane and of butane combustion, then how much more energy propane releases. Excellence
• b Use the given ΔrH and bond energies to calculate the average O–H bond energy in the hydrogen fuel cell reaction. Excellence
• c State the requirement for Galvorn to conduct electricity, then explain why aluminium is both conductive and malleable, linking to its stated uses. Excellence

The 2023 paper ↗ Marking schedule ↗

Question One

Glucose ferments to ethanol and CO₂; ethanol's Lewis structure; hand sanitiser evaporation.

• C₆H₁₂O₆ → 2CH₃CH₂OH + 2CO₂, ΔrH = −72 kJ mol⁻¹; M(CH₃CH₂OH) = 46.0 g mol⁻¹

• a State whether the fermentation is endo/exothermic with a reason, draw a labelled energy diagram, and calculate the energy change when 161 g of ethanol forms. Merit
• b Compare and contrast the shape and bond angles around the carbon and oxygen atoms in ethanol, with reference to VSEPR theory. Excellence
• c Identify the sign of ΔrH for ethanol evaporating, then explain why ethanol readily evaporates and why this cools the hand — referring to energy transfer and to ethanol's structure and bonding. Merit

Question Two

Ethanol combustion produces CO₂ and H₂O; CO₂ and H₂O compared for polarity; a catalytic converter contains palladium.

• CH₃CH₂OH + 3O₂ → 2CO₂ + 3H₂O, ΔrH = −1370 kJ mol⁻¹; C–C 348, C–H 413, C–O 358, C=O 805, O–H 463 kJ mol⁻¹

• a Use the given ΔrH and bond energies to calculate the average O=O bond energy. Excellence
• b Draw the bond dipoles on CO₂, identify the polarity of CO₂ and H₂O, then compare and contrast the factors that determine their polarity. Excellence
• c Complete a solid-type/particle/forces table for CO and Pd, then explain palladium's high melting point using structure and bonding. Merit

Question Three

Lewis structures for PH₃, BCl₃ and COBr₂; carbonic dibromide formation and storage; conductivity of COBr₂ vs LiBr; solubility of LiBr.

• 2C + O₂ + 2Br₂ → 2COBr₂, ΔrH = −145 kJ mol⁻¹; M(COBr₂) = 187.8 g mol⁻¹; 1 mL COBr₂ liquid has mass 2.52 g

• a Draw the Lewis structure and name the shape for PH₃, BCl₃ and COBr₂. Achieved
• b Calculate the mass of COBr₂ formed when 1150 kJ is released, and determine whether it fits in a 1 L flask. Excellence
• c Elaborate on the electrical conductivity of COBr₂ and LiBr, referring to the structure and bonding in each. Excellence
• d Explain why LiBr cannot dissolve in cyclohexane but can dissolve in water, referring to the attractive forces between particles. Excellence

The 2022 paper ↗ Marking schedule ↗

Question One

Refrigerant molecules NH₃, CO₂ and N₂; freon-11 (CCl₃F) and sulfur dioxide compared for shape; freon-11 evaporating to cool a refrigerator.

• CCl₃F(l) → CCl₃F(g), ΔrH = +25.2 kJ mol⁻¹
• Freon-11 bond angle 109.5° (4 regions); SO₂ bond angle 120° (3 regions)

• a Draw the Lewis diagram for NH₃, CO₂ and N₂, and name their shapes. Achieved
• b Compare and contrast the shape and bond angles of freon-11 (CCl₃F) with sulfur dioxide (SO₂). Excellence
• c(i) Draw a labelled energy diagram for the evaporation of freon-11 (CCl₃F(l) → CCl₃F(g), ΔrH = +25.2 kJ mol⁻¹), showing reactants, products, and ΔrH. Achieved
• c(ii) By referring to both the change in enthalpy and the attractive forces between particles in freon-11, explain how its evaporation cools a refrigerator. Excellence

Question Two

Freon-11 produced from carbon tetrachloride and hydrogen fluoride; freon-11 causes ozone decomposition in the upper atmosphere; a modern refrigerant, Compound A (C₃H₂F₄).

• CCl₄ + HF → CCl₃F + HCl, ΔrH° = −21 kJ mol⁻¹; C–F 485, H–F 567, H–Cl 431 kJ mol⁻¹
• 2O₃(g) → 3O₂(g), ΔrH = −285 kJ mol⁻¹, M(O₃) = 48.0 g mol⁻¹

• a(i) Use the given ΔrH° and bond energies to calculate the average bond energy of the C–Cl bond. Excellence
• a(ii) Identify the polarity of freon-11 (CCl₃F) and carbon tetrachloride (CCl₄). Achieved
• a(iii) Compare and contrast the factors that influence the polarity of freon-11 and carbon tetrachloride. Excellence
• b Calculate the amount of energy released when 126 g of ozone, O₃(g), is decomposed into oxygen gas. Merit
• c(i) Classify Compound A (C₃H₂F₄) as ionic, molecular, metallic, or covalent network. Achieved
• c(ii) Using your knowledge of structure and bonding, explain why Compound A is able to evaporate at room temperature. Merit

Question Three

A solid-type table for freon-11, diamond and lithium bromide; diamond vs graphite conductivity; lithium bromide and potassium bromide dissolving in water.

• LiBr(s) → Li⁺(aq) + Br⁻(aq), ΔrH = −48.8 kJ mol⁻¹, M(LiBr) = 86.8 g mol⁻¹
• KBr(s) → K⁺(aq) + Br⁻(aq), ΔrH = +19.9 kJ mol⁻¹, M(KBr) = 119 g mol⁻¹

• a Complete a table of solid type, particle type, and attractive forces for freon-11 (CCl₃F), diamond, and lithium bromide. Achieved
• b Use your knowledge of structure and bonding to explain why graphite conducts electricity while diamond is an electrical insulator. Excellence
• c(i) Classify the dissolving of solid lithium bromide in water as exothermic or endothermic, with a reason. Achieved
• c(ii) Given 20.0 g of LiBr dissolves in one beaker, calculate the mass of solid KBr needed in a second beaker to produce an energy change of equal magnitude. Merit
• c(iii) By considering the enthalpy change of each process, explain any difference in the resultant temperatures of the two solutions (no calculation needed). Merit
• c(iv) Use your knowledge of structure and bonding to explain why solid lithium bromide dissolves in water, using a diagram to illustrate the process. Excellence

Grades above are read from each year's own Achievement/Merit/Excellence evidence statement, condensed to the actual task — the schedules also grade holistically per question on a 0–8 scale, not a fixed mark per bullet.

Past exams & resources

⏱ Timed opens the paper and starts a countdown matching the exam length. Official NZQA PDFs. If a link 404s, that year’s paper may sit under a slightly different code: browse the NZQA subject page.