Enthalpy Change
Energy-profile and enthalpy reasoning, including bond enthalpy calculations and thermal process comparisons.
This route helps when you keep missing the same type of question across different topics. Use it to combine lesson notes with linked practice and tools in one place.
Notes and Hubs in This Route
- Bond Breaking and Bond Forming
Explain qualitatively why reactions are exothermic or endothermic by comparing energy absorbed in bond breaking with energy released in bond making.
- Calculating Heat from Molar Enthalpy (Optional)
Optional enrichment: scale a supplied molar enthalpy, distinguish signed heat from energy released, and use the balanced equation’s reacting amount.
- Endothermic Reactions
Endothermic reactions: definition, ΔH is positive, and how to interpret energy profile diagrams and activation energy in exam questions.
- Energy Changes in Chemical Reactions
K324 and 6092 energy changes hub: enthalpy, energy profiles, and qualitative bond-breaking and bond-making explanations.
- Exothermic Reactions
Exothermic reactions: definition, ΔH is negative, and how to interpret energy profile diagrams and activation energy without common traps.
- Introduction to Energy Changes
Follow heat between the reacting system and its surroundings, distinguish exothermic and endothermic changes, and use the sign of ΔH.
- Reading and Drawing Energy Profiles
Read and draw exothermic and endothermic profiles, distinguish activation energy from enthalpy change, and add a catalysed pathway with the same endpoints.
- Bond Energy, Bond Length and Bond Polarity (A Level)
Define bond energy and bond length, and compare covalent bond reactivity using bond energy, bond length, and bond polarity.
- Chemical Bonding (A Level)
A Level chemical bonding notes: ionic/covalent/dative bonding, VSEPR shapes, sigma and pi bonds, intermolecular forces, and structure–property links.
- Dative Bonding and Common Examples (A Level)
Describe coordinate (dative covalent) bonding in ammonium ions and aluminium chloride dimers with the correct electron-pair origin.
- Intermolecular Forces and Properties (A Level)
Compare London forces, permanent dipole–dipole, and hydrogen bonding, and explain how IMF strength affects boiling point, solubility, and viscosity.
- Ionic and Covalent Bonding Models (A Level)
Describe ionic, covalent and metallic bonding as electrostatic attractions, and draw the syllabus dot-and-cross examples.
- Molecular Shapes and Bond Angles (VSEPR) (A Level)
Use VSEPR to predict 3D shapes and bond angles, including lone pair effects and common molecules like NH3, H2O, CO2, and SF6.
- Sigma and Pi Bonds (Orbital Overlap) (A Level)
Describe covalent bonding through head-on and sideways overlap of s and p orbitals, giving sigma and pi bonds.
- Solids: Structure and Physical Properties (A Level)
Describe the five specified solid lattices, link bonding to physical properties, and deduce structure from property data.
- Bond Enthalpy Calculations (A Level)
Estimate reaction enthalpy using average bond enthalpies (ΔH ≈ Σ bonds broken − Σ bonds formed), with sign conventions and exam pitfalls.
- Calorimetry (q = mcΔT) (A Level)
Perform calorimetry calculations using q = mcΔT, then convert to ΔH per mole with correct signs, units, and heat-loss corrections.
- Energetics & Thermodynamics (A Level)
A Level energetics and thermodynamics notes: calorimetry, Hess and Born–Haber cycles, lattice energy, entropy, and Gibbs free energy (ΔG) reasoning.
- Enthalpy Changes and Energy Profiles (A Level)
Use energy profile diagrams to interpret ΔH and activation energy, and write correct exothermic/endothermic explanations.
- Hess’ Law and Cycles (A Level)
Use Hess’ law to build enthalpy cycles and calculate unknown ΔH values from formation/combustion data, with clean sign/multiple handling.
- Lattice Energy and Born–Haber Cycles (A Level)
Define lattice energy, predict trends with ionic charge/radius, and use Born–Haber cycles to connect lattice energy to formation enthalpy.