Question

alka - seltzer gives off carbon dioxide when added to water. *
this is a physical change
this is a chemical change
sodium and potassium react violently with water. *
this is a physical change
this is a chemical change
water is absorbed by a paper towel. *
this is a physical change
this is a chemical change

Explanation:

1. When Alka - Seltzer reacts with water and gives off carbon dioxide, new substances are formed. A chemical change involves the formation of new substances through chemical reactions, so this is a chemical change.
2. When sodium and potassium react with water violently, new substances are produced in the reaction. Thus, it is a chemical change.
3. When water is absorbed by a paper towel, no new substances are formed. The water is just physically moved from one place to another within the paper towel's pores. This is a physical change.

Answer:

1. This is a CHEMICAL change
2. This is a CHEMICAL change
3. This is a PHYSICAL change