Chemical reactions

2. During a chemical reaction, energy may be transferred from e.g. chemical energy to heat, but it is always .....
7. The rows in the periodic table are called .....
9. A chemical reaction that releases heat is .....
11. A substance that is produced during a chemical reaction.
12. In a molecule, chemical energy is stored within chemical .....
13. The ..... of carbon is twelve.
15. This alkali metal can be found in just about every smartphone battery.
16. When wood burns, some of the chemical energy in the wood is released as .....
17. This element has atomic number seven.
19. Elements in group eight have eight ..... electrons.
21. The atomic number of an element is determined by the number of its .....

1. A chemical reaction that absorbs heat is .....
3. Glucose and oxygen may react with carbon dioxide and water during cellular .....
4. The law of ..... states that matter cannot be created or destroyed.
5. Elements in period two have two electron .....
6. The columns in the periodic table are called .....
8. A substance that is consumed during a chemical reaction.
10. The number of carbon atoms in exactly 12 g of 12C is one .....
14. This element has eight protons in its nucleus.
18. Elements in group five have five valence .....
20. An atom that has lost or gained an electron.