Chapter 3 Chemical reactions

5. a chemical reaction in which substances react with oxygen to form oxides.
8. a change in which atoms are rearranged to create new substances.
12. a possible source of danger.
13. some fuels are form over millions of years, and will one day run out.
14. a chemical reaction in which a substance reacts quickly with oxygen and gives out light and heat.
15. a substance that is made in a chemical reaction.
18. in a chemical reaction the total mass of reactants is equal to the total mass of products.
19. substance that speed up a reaction without being used up.
20. chemical formulae represent the reactants and products. The equation shows how atoms are rearranged, and gives the relative amounts of reactants and products.
21. it transfers energy to the surroundings.

1. a chemical reaction in which a compound breaks down due to the action of heat.
2. a way of representing a chemical reaction simply. The reactants are on the left of an arrow, and the products are on the right. The arrow means to make.
3. a variable that can only have whole-number value.
4. a material that burns to transfer useful energy.
6. a starting substance in a chemical reaction.
7. the chance of damage or injury from hazard.
9. decomposition a chemical reaction where a substance breaks down due to the action of heat.
10. a change that is reversible, in which new substances are not made.
11. a fuel made from the remains of animals and plants that died millions of years ago. It includes coal, oil and natural gas.
16. it transfers energy from the surroundings.
17. a type of chemical reaction in which the products can react to form the original reactants and vice versa.