Predict the effect of continuously removing a product from an equilibrium mixture as it forms.

The equilibrium shifts to the right to replace it, so more reactant is converted to product.

Predict the effect of raising the temperature on the position of an equilibrium.

It shifts in the endothermic direction, because taking in energy opposes the rise in temperature.

Predict the effect of lowering the temperature on the position of an equilibrium.

It shifts in the exothermic direction, because releasing energy opposes the fall in temperature.

Predict the effect of increasing the pressure on an equilibrium between gases.

It shifts towards the side with the smaller number of gas molecules, because that reduces the pressure.

OCR GCSE Combined Science Chemistry J250

Chemical Reactions

Topic overview Writing formulae of elements and compounds Balanced equations, and deducing formulae from ions Ionic equations, and state symbols The mole and the Avogadro constant Conservation of mass, and changes of mass in open systems Stoichiometry, and calculating reacting masses Exothermic and endothermic reactions, and reaction profiles Activation energy, and bond energy calculations Oxidation and reduction, by oxygen and by electrons Acids, alkalis and neutralisation The ionic equation for neutralisation, and reactions of acids Dilute and concentrated, weak and strong The pH scale, and hydrogen ion concentration pH as a factor of ten, and measuring pH Products at the electrodes, and molten ionic compounds Electrolysis of aqueous solutions Inert and non-inert electrodes

Elements, Compounds and Mixtures

Topic overview Purity, and melting point data Relative formula mass and empirical formulae Formulations, and separating mixtures Paper and thin layer chromatography Interpreting chromatograms and Rf values Choosing a purification method Metals and non-metals in the Periodic Table Electron arrangement and position in the Periodic Table Ionic, covalent and metallic bonding compared Dot and cross diagrams, and the limits of models Reactions, electron arrangement and Mendeleev's table Carbon's four bonds, and the variety of organic compounds Diamond, graphite, fullerenes and graphene Bond strength, intermolecular forces and predicting state Bulk properties of ionic, molecular and giant structures

Global Challenges

Topic overview Extracting metals by reduction and by electrolysis Biological methods of metal extraction Life cycle assessment Recycling, and the decisions behind it Fractional distillation of crude oil The fractions, and crude oil as a feedstock Dependence on hydrocarbons, and cracking The Earth's early atmosphere, and how oxygen developed The greenhouse effect, and evidence for climate change Effects of carbon dioxide and methane, and air pollutants Producing potable water

Monitoring and Controlling Chemical Reactions

Topic overview Mass of solute, concentration and dilution calculations Measuring the rate of a reaction, and rate graphs Factors affecting rate, and collision theory Surface area and rate Catalysts and how they work Reversible reactions and dynamic equilibrium Changing the conditions of an equilibrium Activation energy, and enzymes as catalysts

Particles

Topic overview The particle model and changes of state Limitations of the particle model How the atomic model changed, and the structure of the atom The size of atoms, and the subatomic particles Calculating protons, neutrons and electrons

Predicting and Identifying Reactions

Topic overview Groups 1, 7 and 0, and why they behave as they do Predicting reactivity from the Periodic Table Reactivity of metals with water and acids Tests for oxygen, hydrogen, carbon dioxide and chlorine

Monitoring and Controlling Chemical Reactions

Changing the conditions of an equilibrium

3 things to know
Paper 10 (Chemistry)

Overview

Le Chatelier’s principle, and the effect on the position of equilibrium of changing concentration, removing a product, raising or lowering the temperature, and changing the pressure, with the compromise conditions for ammonia and sulfur trioxide.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

For the exothermic equilibrium 2SO₂ + O₂ ⇌ 2SO₃, why is a moderately high temperature used and what does raising the pressure do?

Key term

State the principle used to predict how the position of an equilibrium responds to a change in conditions.

Key term

Predict the effect of increasing the concentration of a reactant on the position of an equilibrium.

Questions from this subtopic

Each one with the model answer underneath.

1
State the principle used to predict how the position of an equilibrium responds to a change in conditions.
Model answer
Le Chatelier’s principle: if a change is made to a system at equilibrium, the position of equilibrium shifts in the direction that opposes that change.
2
Predict the effect of increasing the concentration of a reactant on the position of an equilibrium.
Model answer
The equilibrium shifts to the right, so more of the products are formed.
3
Predict the effect of continuously removing a product from an equilibrium mixture as it forms.
Model answer
The equilibrium shifts to the right to replace it, so more reactant is converted to product.
4
Predict the effect of raising the temperature on the position of an equilibrium.
Model answer
It shifts in the endothermic direction, because taking in energy opposes the rise in temperature.
5
Predict the effect of lowering the temperature on the position of an equilibrium.
Model answer
It shifts in the exothermic direction, because releasing energy opposes the fall in temperature.
6
Predict the effect of increasing the pressure on an equilibrium between gases.
Model answer
It shifts towards the side with the smaller number of gas molecules, because that reduces the pressure.

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Chemical Reactions

Elements, Compounds and Mixtures

Global Challenges

Monitoring and Controlling Chemical Reactions

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AMetals are on the left and in the centre, and non-metals are on the right-hand side.

BKI, because potassium loses one electron and iodine gains one.

CCaCl₂, because a calcium atom loses two electrons and each chlorine atom gains one.

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