Which of the following would be evidence that a chemical reaction has occurred? (Select all that apply.) *

a change in shape

a precipitate is formed

an unexpected change in color

the formation of gas bubbles

smoke begins to form

clear liquids remain clear

the odor changes

the substance becomes very cold

1) precipitate is formed

2) unexpected color change

3) formation of gas bubbles

4) smoke forms

5) odor change

6) substance becomes cold

Explanation:

1/3) its a new substance.

2/5) they are both changes to the original substance that cannot be reversed.

4) where theres smoke theres fire, and burning is classified as a type of chemical change.

6) it could possibly be an endothermic reaction, where it absorbs heat and the substance becomes cold.

An unexpected change in color, the odor changes, the temperature changes, precipitation is formed, formation of gas bubbles