KS3 Science · Chemistry
Chemical reactions
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Key words
Chemical reaction A change in which a new substance is made
Physical change A change in which no new substance is made
Reactant A substance you start with in a reaction
Product A new substance made in a reaction
Word equation Shows a reaction using the names of the substances
Conservation of mass The total mass is the same before and after a reaction
Combustion Burning: a reaction with oxygen that gives out heat and light
Fuel A substance that stores energy and is burned to release it
Fire triangle Fuel, oxygen and heat: the three things a fire needs
Oxide A compound of an element joined with oxygen
Hydrocarbon A compound of hydrogen and carbon only, such as methane
Thermal decomposition When heat breaks one substance down into simpler ones
Limewater A clear solution that carbon dioxide turns cloudy
Exothermic Gives out energy, so the surroundings get hotter
Endothermic Takes in energy, so the surroundings get colder
Catalyst Speeds up a reaction and is not used up
Chemical bond The force that holds atoms together in a molecule