Chemical Reactions and Energetics

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infoWhy this? Chemical reactions transform reactants into new products by rearranging atoms, while conserving mass and transferring energy. Distinguishing chemical from physical change and using formulae, particle models, and equations allows us to describe combustion, decomposition, oxidation, and catalysis precisely.

scheduleWhy now? This unit builds on Year 7 distinctions among particles, pure substances, mixtures, and physical separation. It introduces atoms, elements, compounds, formulae, and reaction equations that underpin later study of acids, atomic structure, reactivity, extraction, and the periodic table.

A chemical change involves the formation of a new substance.
Physical changes do not produce new substances, whereas chemical changes do.
Examples of physical changes include melting, freezing, boiling, and dissolving.
Examples of chemical changes include burning, rusting, and neutralisation.
All matter consists of atoms.
Elements consist of only one type of atom.
Different elements exist as solids, liquids, or gases at room temperature, depending on their melting and boiling points.
Atoms were once considered indivisible and the smallest particles of matter.
Elements are pure substances made of only one type of atom.
Compounds are substances made from two or more different elements chemically bonded together.
Compounds have different properties from the elements they are made from, both chemically and physically.
Mixtures are different from compounds because the substances in mixtures are not chemically bonded and retain their individual properties.
Each element has a unique chemical symbol, such as H for hydrogen, O for oxygen, and Na for sodium.
Simple compounds have chemical formulae showing the types and ratios of atoms present, such as H₂O for water and CO₂ for carbon dioxide.
In chemical reactions, reactants are converted into products.
The total mass of reactants equals the total mass of products in a chemical reaction (law of conservation of mass).
Mass may appear to change in reactions if gases are released or absorbed, but the total mass remains constant if all products and reactants are accounted for.
Combustion is the burning of a substance in oxygen, producing oxides.
Complete combustion produces carbon dioxide and water.
Incomplete combustion produces carbon monoxide or soot and water.
Thermal decomposition is the breakdown of a compound using heat, often producing a gas, such as carbon dioxide from metal carbonates.
Exothermic reactions release heat energy.
Endothermic reactions absorb heat energy.
Oxidation is a reaction where oxygen is added to a substance; it can also be defined as the loss of hydrogen.
Catalysts speed up chemical reactions without being used up themselves.
Catalysts are used in processes such as the Haber process (ammonia production), catalytic converters in cars, and hydrogen peroxide decomposition.

rocket_launchYou must be able to

Identify whether a change is physical or chemical using particle models and observable evidence.
Use word and symbol equations, including state symbols, to represent chemical and physical changes.
Use melting and boiling point data to determine the state of an element at room temperature.
Identify elements and compounds from particle diagrams.
Compare and contrast elements, compounds, and mixtures using particle models and examples.
Recall and write the symbols for a wide range of elements and simple compounds.
Interpret and write chemical formulae, using subscript numbers to denote the number and ratio of atoms in compounds such as H₂O and CH₄, and identify O₂ as a molecule of the element oxygen rather than a compound.
Interpret particle diagrams to show how atoms are rearranged during a chemical reaction.
Write word equations for chemical reactions, including combustion and thermal decomposition.
Construct particle models to represent chemical reactions using chemical formulae.
Calculate changes in mass during chemical reactions, including those involving gases.
Describe and explain observations from combustion and thermal decomposition reactions, including colour changes and gas evolution.
Test for carbon dioxide using limewater in the context of thermal decomposition.
Interpret experimental data to determine whether a reaction is exothermic or endothermic.
Link exothermic and endothermic reactions to energy level diagrams and conservation of energy.
Make and record observations about chemical changes, linking them to oxidation and conservation of mass.
Define oxidation in terms of both addition of oxygen and loss of hydrogen, and give examples.
Explain how catalysts work, including their effect on activation energy and reaction profiles.
Identify and explain the use of catalysts in industrial and everyday processes.

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