In a chemical reaction, the reactants contain 385 kj of chemical energy, and the products contain 366 kj of chemical energy. in order for energy to be conserved, what must happen?

In order for energy to be conserved 19 KILO JOULE OF ENERGY MUST BE RELEASED AS HEAT.
In chemical reactions, energy is always conserved. In the question given above, there is a difference of 19 kj in the energy quantity between the reactants and the products. The reactants has more energy than the products, this excess energy is given off as heat during the reaction.

The answer to that would be magnesium