Sort the following situations into chemical change or physical change:
1. salt dissolves in water
2. hydrochloric acid reacts with magnesium to produce hydrogen gas
3. a piece of copper is cut in half
4. a sugar cube is ground up
5. water is heated and changed to steam
6. iron rusts
7. ethyl alcohol evaporates
8. ice melts
9. milk sours
10. sugar dissolves in water
11. sodium and potassium react violently with water
12. pancakes cook on a griddle
13. grass grows on a lawn
14. a tire is inflated with air
15. food is digested in the stomach
16. water is absorbed by a paper towel
17. ethyl alcohol boils at 79 egress celsius
18. paper burns
19. water freezes at 0 degrees celsius
20. fireworks explode
21. alka-seltzer gives off carbon dioxide when added to water
22. clouds form in the sky