State whether changing the concentration of one substance in an equilibrium mixture affects only that substance.

No, the concentrations of all the reactants and products change until a new equilibrium is established.

Explain why a change in concentration disturbs a system that was at equilibrium.

The forward and reverse reactions are no longer going at the same rate, so the mixture keeps changing until those rates become equal again.

State and explain what happens to the amount of product when the concentration of a reactant is increased.

More product is formed until equilibrium is reached again, because the system shifts towards the products to use up the added reactant.

In the equilibrium A + B ⇌ C + D, extra A is added. State the direction of the shift and explain why.

The equilibrium shifts to the right, forming more C and D, because the system opposes the increase by removing some of the added A.

State and explain what happens when the concentration of a product in an equilibrium mixture is decreased.

More reactants react and the equilibrium shifts towards the products, because the system acts to replace the product that was removed.

AQA GCSE Combined Science Chemistry 8464

Atomic Structure and the Periodic Table

Topic overview Atoms, elements and compounds Word equations, symbols and balanced equations Mixtures From the plum pudding model to the nuclear model Bohr, Chadwick and the modern model of the atom Relative electrical charges of subatomic particles Size and mass of atoms Relative atomic mass and electronic structure The periodic table Development of the periodic table Metals and non-metals Group 0 Group 1 Group 7

Bonding, Structure, and the Properties of Matter

Topic overview Chemical bonds, including metallic bonding Ionic bonding Ionic compounds Covalent bonding and how it is represented The three states of matter and changes of state Predicting state, state symbols, and the limits of the particle model Properties of ionic compounds Properties of small molecules Polymers and giant covalent structures Properties of metals and alloys, and why metals conduct Diamond and graphite Graphene and fullerenes

Chemical Analysis

Topic overview Pure substances Formulations Chromatography Tests for hydrogen, oxygen, carbon dioxide and chlorine

Chemical Changes

Topic overview The reactivity series Metal oxides, extraction, and redox in terms of electrons Acids reacting with metals, neutralisation and salts Soluble salts The pH scale and neutralisation Strong and weak acids The process of electrolysis, and molten ionic compounds Using electrolysis to extract metals Electrolysis of aqueous solutions Representation of reactions at electrodes as half equations

Chemistry of the Atmosphere

Topic overview The Earth's early atmosphere How oxygen increased and carbon dioxide decreased The gases in today's atmosphere, and which are greenhouse gases Human activities which contribute to an increase in greenhouse gases in the atmosphere Global climate change and carbon footprints Atmospheric pollutants from fuels, and their effects

Energy Changes

Topic overview Exothermic and endothermic reactions Everyday uses, and investigating temperature change Reaction profiles The energy change of reactions

Organic Chemistry

Topic overview Crude oil, hydrocarbons and alkanes Fractional distillation and petrochemicals Properties of hydrocarbons Cracking, and testing alkenes with bromine water Why cracking is useful, and equations for it

Quantitative Chemistry

Topic overview Conservation of mass and balanced chemical equations Relative formula mass and concentration of solutions Mass changes when a gas is involved, and measurement uncertainty Moles Amounts of substances in equations, and balancing using moles Limiting reactants

The Rate and Extent of Chemical Change

Topic overview Measuring the mean rate of a reaction Rate from graphs, and the gradient of a tangent Factors which affect the rates of chemical reactions Collision theory and activation energy Catalysts Reversible reactions and dynamic equilibrium The effect of changing conditions on equilibrium The effect of changing concentration The effect of temperature changes on equilibrium The effect of pressure changes on equilibrium

Using Resources

Topic overview Using the Earth's resources and sustainable development Producing potable water in the UK Desalination, and analysing water samples Waste water treatment Alternative methods of extracting metals Life cycle assessment Ways of reducing the use of resources

The Rate and Extent of Chemical Change

The effect of changing concentration

3 things to know
Chemistry Paper 2

Overview

What happens to a mixture when one concentration changes, why the whole system shifts, the effects of adding a reactant or removing or adding a product, and the hydrogen iodide and ammonia equilibria as examples.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

For an equilibrium A + B ⇌ C, explain the shift when more reactant is added, when C is removed, and when C is added.

Key term

For hydrogen iodide and ammonia equilibria, explain what happens when a product is removed or a reactant reduced, and why industry removes product continuously.

Key term

Describe what happens to a mixture at equilibrium immediately after the concentration of one of the substances in it is changed.

Questions from this subtopic

Each one with the model answer underneath.

1
Describe what happens to a mixture at equilibrium immediately after the concentration of one of the substances in it is changed.
Model answer
The mixture is no longer at equilibrium, and the concentrations of all the substances change until equilibrium is reached again.
2
State whether changing the concentration of one substance in an equilibrium mixture affects only that substance.
Model answer
No, the concentrations of all the reactants and products change until a new equilibrium is established.
3
Explain why a change in concentration disturbs a system that was at equilibrium.
Model answer
The forward and reverse reactions are no longer going at the same rate, so the mixture keeps changing until those rates become equal again.
4
State and explain what happens to the amount of product when the concentration of a reactant is increased.
Model answer
More product is formed until equilibrium is reached again, because the system shifts towards the products to use up the added reactant.
5
In the equilibrium A + B ⇌ C + D, extra A is added. State the direction of the shift and explain why.
Model answer
The equilibrium shifts to the right, forming more C and D, because the system opposes the increase by removing some of the added A.
6
State and explain what happens when the concentration of a product in an equilibrium mixture is decreased.
Model answer
More reactants react and the equilibrium shifts towards the products, because the system acts to replace the product that was removed.

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Atomic Structure and the Periodic Table

Bonding, Structure, and the Properties of Matter

Chemical Analysis

Chemical Changes

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AMolecular size controls boiling point, viscosity and flammability.

BSmall molecules make gases and petrol that ignite easily.

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