Explain why a non-rechargeable battery eventually goes flat.

The chemicals inside it are used up by the reaction, so no further reaction can take place to produce a potential difference.

What must be present between the two electrodes of a chemical cell, and why?

An electrolyte, so that ions can move between the electrodes and complete the circuit.

In a simple cell made from two different metals, what decides how large the potential difference is?

How far apart the two metals are in reactivity: the bigger the difference, the larger the potential difference.

Why does a cell with the same metal used for both electrodes produce no potential difference?

There is no difference in reactivity between the electrodes, so no overall reaction takes place.

OCR GCSE Chemistry A J248

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 Nanoparticles: size and surface area to volume Uses and risks of nanoparticulate materials

Global Challenges

Topic overview Extracting metals by reduction and by electrolysis Biological methods of metal extraction Rate against yield in industry, and reaction conditions The Haber process and fertiliser production Nitrogen, phosphorus and potassium in agriculture Life cycle assessment Recycling, and the decisions behind it Alloys, and the corrosion of metals Comparing glass, ceramics, polymers, composites and metals Functional groups and homologous series Predicting the products of organic reactions Addition polymerisation Condensation polymerisation, and making a polymer DNA and other natural polymers Fractional distillation of crude oil The fractions, and crude oil as a feedstock Dependence on hydrocarbons, and cracking Chemical cells and fuel cells 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 Concentration in mol/dm³, and titration Titration calculations, and the mass of a solute Molar gas volume and the volumes of gases Theoretical mass and percentage yield Atom economy, and choosing a reaction pathway 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 Transition metals Predicting reactivity from the Periodic Table Reactivity of metals with water and acids Tests for oxygen, hydrogen, carbon dioxide and chlorine Tests for aqueous cations and anions Flame tests, and identifying metal ions Identifying a species from test results Instrumental methods of analysis

Global Challenges

Chemical cells and fuel cells

2 things to know
Paper 4

Overview

What a chemical cell is, why it runs until a reactant is used up and a battery goes flat, the electrolyte and the difference in reactivity that sets the potential difference, making a cell last longer, the hydrogen–oxygen fuel cell with its equation, electrodes and water product, its advantages and disadvantages in cars and spacecraft, and whether a hydrogen car is free of carbon dioxide emissions.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is a chemical cell?

Key term

For how long does a chemical cell produce a potential difference?

Questions from this subtopic

Each one with the model answer underneath.

1
What is a chemical cell?
Model answer
A device in which a chemical reaction produces a potential difference between two electrodes, which can drive a current round a circuit.
2
For how long does a chemical cell produce a potential difference?
Model answer
Until one of the reactants has been used up, after which the reaction stops and the potential difference falls to zero.
3
Explain why a non-rechargeable battery eventually goes flat.
Model answer
The chemicals inside it are used up by the reaction, so no further reaction can take place to produce a potential difference.
4
What must be present between the two electrodes of a chemical cell, and why?
Model answer
An electrolyte, so that ions can move between the electrodes and complete the circuit.
5
In a simple cell made from two different metals, what decides how large the potential difference is?
Model answer
How far apart the two metals are in reactivity: the bigger the difference, the larger the potential difference.
6
Why does a cell with the same metal used for both electrodes produce no potential difference?
Model answer
There is no difference in reactivity between the electrodes, so no overall reaction takes place.

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Chemical Reactions

Elements, Compounds and Mixtures

Global Challenges

Monitoring and Controlling Chemical Reactions

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AThe products sit at a higher energy level than the reactants.

BThe activation energy, the energy that must be supplied before the reaction can happen.

CThe reactants, the products, the activation energy and the overall energy change.

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Sodium ions give a bright yellow flame colour.

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