If we reverse the reaction to read z + q → x + y, the +δh would be a -δh. does this indicate that heat is given off or absorbed in the reverse reaction? -given off -absorbed

Reactants.  

Step-by-step explanation:

The equation for the reverse reaction is

Z + Q ⟶ X + Y; ΔH < 0

A negative ΔH indicates that the energy has been given off.

The products X + Y are at a lower energy level than the reactants Z + Q, and the excess energy has been transferred to the surroundings.

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.