3. A student performed the following reaction in the lab:
2Mg + O2 → 2MgO
She isolated 25.8g of MgO. She also knew how to calculated the expected or the theoretical yield based on the amount of her starting materials (She was of course one of Dr. W’s prize students). She calculated the theoretical yield to be 28.9g.
What was the % yield for this experiment?

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.

it would be a gas formation