Chemical Reactions

1. A change in which one or more substances combine or break apart to form new substances
5. A number in front of a chemical formula in an equation that indicates how many molecules or atoms of each reactant and product are involved in a reaction
7. A solid that forms from a solution during a chemical reaction
11. A chemical reaction in which two or more simple substances combine to form a new, more complex substance
13. The amount of one material in a certain volume of another material
16. A substance that undergoes change in a reaction
18. A biological catalyst that lowers the activation energy of reactions in cells
20. A reaction that releases energy in the form of heat
21. A substance formed as a result of a chemical reaction

2. A material that decreases the rate of reaction
3. A chemical reaction that breaks down compounds into simpler products
4. A material that releases energy when it burns
6. A material that increases the rate of reaction by lowering the activation energy
8. A rapid reaction between oxygen and fuel that results in fire
9. A system in which matter can enter from or escape to the surroundings
10. A system in which no matter is allowed to enter or leave
12. Anything that has mass and occupies space
14. A reaction that absorbs energy in the form of heat
15. A reaction in which one element replaces another in a compound or when two elements in different compounds trade places
17. The study of properties of matter and how matter changes
19. A change in substance that does not change its identity