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EnglandChemistry

3.1 Physical chemistry

12 dot points across 12 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

What is pH really measuring, and how do buffers resist change?

Bronsted-Lowry acids and bases, the pH scale and calculating pH of strong acids, the ionic product of water Kw, weak acids and Ka, pH curves and titrations, and buffer action.
A focused answer to AQA A-Level Chemistry 3.1.12, covering Bronsted-Lowry acids and bases, the pH scale, the ionic product of water Kw, weak acids and Ka, pH curves and indicators, and how buffers work.
13 min answer →

How do chemists count atoms and link mass, moles and volume?

The Avogadro constant and the mole, the ideal gas equation, empirical and molecular formulae, balanced equations and associated calculations, percentage yields and atom economy, and concentrations of solutions.
A focused answer to AQA A-Level Chemistry 3.1.2, covering the mole and Avogadro constant, the ideal gas equation, empirical and molecular formulae, reacting mass and solution calculations, percentage yield and atom economy.
10 min answer →

What is an atom made of, and how do we measure and arrange its particles?

Fundamental particles (protons, neutrons, electrons), mass number and atomic number, isotopes, the time of flight (TOF) mass spectrometer, relative atomic mass, electron configuration in sub-shells, and the trends in ionisation energy across periods and down groups.
A focused answer to AQA A-Level Chemistry 3.1.1, covering the fundamental particles, isotopes, the time of flight mass spectrometer, relative atomic mass, sub-shell electron configuration and ionisation energy trends.
10 min answer →

How do atoms join together, and how does bonding shape molecules and their properties?

Ionic, covalent, dative covalent and metallic bonding, the four crystal structures, electron pair repulsion theory and molecular shapes, bond polarity and electronegativity, and the forces between molecules including van der Waals, dipole-dipole and hydrogen bonding.
A focused answer to AQA A-Level Chemistry 3.1.3, covering ionic, covalent, dative and metallic bonding, the four crystal structures, electron pair repulsion shapes, electronegativity and polarity, and intermolecular forces.
11 min answer →

How do reversible reactions settle into balance, and how do we measure that balance?

Dynamic equilibrium, Le Chatelier's principle and the effect of changing concentration, pressure and temperature, the role of a catalyst, and the equilibrium constant Kc and its calculation.
A focused answer to AQA A-Level Chemistry 3.1.6, covering dynamic equilibrium, Le Chatelier's principle, the effects of concentration, pressure, temperature and catalysts, and writing and calculating the equilibrium constant Kc.
11 min answer →

How do redox reactions generate electricity, and how do we predict their feasibility?

Electrode potentials and the standard hydrogen electrode, electrochemical cells and cell EMF, using standard electrode potentials to predict feasibility, and commercial cells and fuel cells.
A focused answer to AQA A-Level Chemistry 3.1.11, covering electrode potentials and the standard hydrogen electrode, electrochemical cells and EMF, predicting feasibility from standard electrode potentials, and commercial and fuel cells.
12 min answer →

Why do some reactions release heat while others absorb it, and how do we measure it?

Enthalpy change, exothermic and endothermic reactions, standard enthalpy changes (formation, combustion), calorimetry and the equation q = mcDeltaT, Hess's law and enthalpy cycles, mean bond enthalpies.
A focused answer to AQA A-Level Chemistry 3.1.4, covering enthalpy change, exothermic and endothermic reactions, standard enthalpy definitions, calorimetry, Hess's law cycles and mean bond enthalpy calculations.
11 min answer →

How do we express equilibrium for gas-phase reactions using partial pressures?

Mole fractions and partial pressures, the equilibrium constant Kp written in terms of partial pressures, calculating Kp, and the effect of changing conditions on Kp.
A focused answer to AQA A-Level Chemistry 3.1.10, covering mole fractions and partial pressures, writing and calculating the equilibrium constant Kp for gaseous equilibria, and the effect of changing conditions on Kp.
10 min answer →

What controls how fast a chemical reaction goes?

Collision theory, the Maxwell-Boltzmann distribution, the effect of temperature, concentration, pressure, surface area and catalysts on rate, and how catalysts lower activation energy.
A focused answer to AQA A-Level Chemistry 3.1.5, covering collision theory, the Maxwell-Boltzmann distribution, the effects of temperature, concentration, pressure and surface area on rate, and how catalysts work.
9 min answer →

How do we track electron transfer in chemical reactions?

Oxidation states (rules for assigning them), oxidation as loss of electrons and reduction as gain, oxidising and reducing agents, and writing and balancing half-equations and overall redox equations.
A focused answer to AQA A-Level Chemistry 3.1.7, covering oxidation states and the rules for assigning them, oxidation and reduction in terms of electrons, oxidising and reducing agents, and constructing balanced half-equations and overall redox equations.
9 min answer →

How can we express reaction rate as an equation and find the mechanism?

Rate equations, orders of reaction and the rate constant k, determining orders from initial-rate and concentration-time data, the Arrhenius equation, and using the rate-determining step to deduce a mechanism.
A focused answer to AQA A-Level Chemistry 3.1.9, covering rate equations and orders of reaction, the rate constant k, determining orders from data, the Arrhenius equation, and the rate-determining step in mechanisms.
12 min answer →

What really decides whether a reaction is feasible?

Born-Haber cycles and lattice enthalpies, enthalpies of solution and hydration, entropy change, and Gibbs free energy DeltaG = DeltaH - T DeltaS as the test of feasibility.
A focused answer to AQA A-Level Chemistry 3.1.8, covering Born-Haber cycles and lattice enthalpies, enthalpies of solution and hydration, entropy change, and Gibbs free energy as the measure of reaction feasibility.
12 min answer →