Key term
AQA AS-Level Chemistry 7405
Atomic Structure
Topic overviewFundamental ParticlesMass Number and IsotopesTime of Flight Mass Spectrometry: Ionisation and AccelerationTime of Flight Mass Spectrometry: Drift, Detection and Calculating m/zElectron Configuration: Sub-shells and OrbitalsElectron Configuration: Writing Configurations for Atoms and IonsIonisation Energies and Periodic Trends
Amount of Substance
Topic overviewRelative Atomic and Molecular MassThe Mole and the Avogadro ConstantThe Ideal Gas EquationEmpirical and Molecular FormulaBalanced Equations and Reaction CalculationsAtom Economy and Percentage YieldAcid-Base Titrations: Principles, Indicators and ApparatusAcid-Base Titrations: Standard Solutions and Calculations
Bonding
Topic overviewIonic BondingCovalent, Dative Covalent and Metallic BondingCrystal Structures: Giant Ionic Lattices and DiamondCrystal Structures: Graphite and Simple Molecular SolidsShapes of Molecules and Ions: VSEPR and Electron Pair RepulsionShapes of Molecules and Ions: Predicting Shapes and Bond AnglesElectronegativity and Bond PolarityIntermolecular Forces
Energetics and Thermodynamics
Kinetics
Chemical Equilibria
Redox and Electrochemistry
Periodicity and Group Chemistry
Topic overviews, p, d and f Block ClassificationTrends in Period 3Group 2 Trends in Atomic Radius, Ionisation Energy and Melting PointReactions of Group 2 with WaterSolubility Trends of Group 2 HydroxidesSolubility Trends of Group 2 SulfatesUses of Group 2 CompoundsTest for Sulfate IonsTrends in Electronegativity and Boiling Point of HalogensHalogens as Oxidising Agents and Displacement ReactionsHalide Ions as Reducing Agents: Chloride and BromideHalide Ions as Reducing Agents: Iodide, and the EquationsTest for Halide Ions Using Silver NitrateTests for Ammonium, Group 2, Hydroxide and Carbonate IonsReactions of Chlorine with WaterReactions of Chlorine with Cold Dilute NaOH and Water Treatment
Introduction to Organic Chemistry
Hydrocarbons
Topic overviewAlkanes, Fractional Distillation and CrackingCombustion of Alkanes and PollutantsFree Radical Chlorination of AlkanesAlkenes: Structure, Bonding and Electrophilic AdditionMarkovnikov's Rule and Carbocation StabilityAddition Polymers and Repeating UnitsProperties and Uses of Polyalkenes
Halogenoalkanes, Alcohols and Organic Analysis
Topic overviewNucleophilic Substitution of HalogenoalkanesEffect of Bond Enthalpy on Reaction RateElimination Reactions and Competing MechanismsCFCs and Ozone DepletionIndustrial Production of AlcoholsBiofuels and Carbon NeutralityClassification and Oxidation of AlcoholsDistinguishing Aldehydes and KetonesElimination of Water from AlcoholsTest-Tube Reactions for Functional GroupsMass Spectrometry and Molecular FormulaInfrared Spectroscopy, Functional Groups and Global Warming
Chemical Equilibria
- 3 subtopics
- 15 things to know
- Papers 1, 2 and 3
What Chemical Equilibria covers
Chemical equilibria is examined on Papers 1, 2 and 3, with Kp on Paper 1 only. It covers what a dynamic equilibrium is, how Le Chatelier's principle predicts the effect of a change, why industry settles for compromise conditions, and the two equilibrium constants.
Where it is assessed
Papers 1, 2 and 3
Physical chemistry drawn on by both written papers.
Check the AQA specification ↗The 3 subtopics
Each one has its own page. AQA AS Chemistry students sit this topic in the first year.
- Dynamic Equilibrium and Le Chatelier's PrincipleThe conditions for dynamic equilibrium, and predicting the effect of concentration, pressure and temperature.Open →
- Industrial Compromise ConditionsWhy the Haber process trades yield against rate and cost: the compromise temperature and pressure, and what the catalyst does and does not change.Open →
- The Equilibrium Constant KcWriting the Kc expression, calculating it from equilibrium amounts, and working out its units.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
What are partial pressure and mole fraction?
Key term
In a dynamic equilibrium, how do the rates of the forward and reverse reactions compare?
Process
Why is a compromise temperature used in industrial processes involving exothermic reversible reactions?
Key term
What happens to the equilibrium yield of an exothermic reaction if the temperature is too low?
Key term
What is the equilibrium constant Kc?
Key term
For a reversible reaction at equilibrium, what does the expression for Kc contain?
Key term
What is the partial pressure of a gas in a mixture?
Key term
What is the equilibrium constant Kp used for?
Key term
What type of equilibrium systems does Kp apply to?
Key term
At dynamic equilibrium, what happens to the concentrations of reactants and products?
Process
What happens to the rate of reaction if the temperature is too low in an industrial process?
Key term
How are stoichiometric coefficients incorporated into a Kc expression?
Key term
What is the mole fraction of a gas in a mixture?
Key term
In the expression for Kp, what quantity is used instead of concentration?
Take Chemical Equilibria further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Mole fraction vs Partial pressure
Mole fraction: the moles of one gas divided by the total moles of gas. Partial pressure: the contribution one gas makes to the total pressure.
Dynamic equilibrium vs Static equilibrium
Dynamic equilibrium: forward and reverse reactions continuing at equal rates in a closed system. Static equilibrium: a state with no continuing opposing reactions.
Questions from this topic
Each one with the model answer underneath.
- 1
What is meant by a dynamic equilibrium?
Model answer
A dynamic equilibrium is a state where the forward and reverse reactions occur at equal rates, with no net change in concentrations of reactants and products.
- 2
What two conditions must be met for a dynamic equilibrium to be established?
Model answer
The system must be closed (no substances can enter or leave) and the forward and reverse reactions must occur at the same rate.
- 3
In a dynamic equilibrium, how do the rates of the forward and reverse reactions compare?
Model answer
The rates of the forward and reverse reactions are equal.
- 4
At dynamic equilibrium, what happens to the concentrations of reactants and products?
Model answer
Reactant and product concentrations hold steady.
- 5
State Le Chatelier's principle.
Model answer
Le Chatelier's principle states that if a system at equilibrium is subjected to a change in conditions, the position of equilibrium shifts to counteract the change.
- 6
What happens to the position of equilibrium when the concentration of a reactant is increased?
Model answer
The position of equilibrium shifts to the right (towards products) to use up the added reactant.
What is inside Levo
Six ways to work the same material.
Chemical Equilibria revision questions
- Is Chemical Equilibria examined at AS in AQA Chemistry?
- Yes. It sits in Papers 1, 2 and 3, which you take in the first year, so it is on the AS paper as well as counting towards the full A level.
- What does Chemical Equilibria cover in AQA AS-Level Chemistry?
- 3 subtopics: dynamic equilibrium and le chatelier's principle, industrial compromise conditions and the equilibrium constant kc. Each one has its own page with questions and model answers.
- How is Chemical Equilibria organised?
- By the AQA 7405 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Chemical Equilibria, on a schedule.
Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.
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