Unit 4

3. the substance present at the beginning of a chemical reaction
4. occurs when an atom gains electrons in a reaction or when a substance gains a hydrogen or loses an oxygen atom in a chemical reaction
8. the tendency of the substance to react with other substances
10. the SI unit for the amount of a substance
11. a chemical reaction that takes in heat
13. a catalyst used by living things to increase the speed of a natural chemical process
14. a strong chemical bond that is formed by the attraction between two ions of opposite charges
16. the point at which the rate of the forward reaction is equal to the rate of the backward reaction
18. a chemical bond where positive metal ions form a lattice structure with freely moving electrons between them
19. reaction a reaction in which the products can never be turned back into the reactants
20. a new substance in a chemical reaction

1. an interaction between the atoms of two substances where the atoms rearrange to form two new molecules
2. a substance which speeds up a chemical reaction without being changed by the reaction
5. the measure of the strength of a solution, i.e., the amount of the solute in the solvent
6. occurs when an atom loses electrons in a reaction or when a substance loses a hydrogen or gains an oxygen in a chemical reaction
7. s chemical reaction that gives off heat
9. a chemical bond between two atoms in which each atom shares an electron
12. reaction a reaction in which under the right conditions the products can be turned back into the reactants
15. a reaction that primarily involves the transfer of electrons between two substances
17. an atom or group of atoms that has become charged by gaining or losing one or more electrons