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.

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.