What are the first 20 elements and how do i memorize it within a day?

During this chemical reaction energy is released. in the chemistry lab, this would be indicated by an increase in temperature or, if the reaction took place in a test tube, the test tube would feel warmer to the touch. reactions like this release energy because a) the reaction requires activation energy. b) the reactants have less potential energy than the products. c) the reactants have more potential energy than the products. d) the mass of the products is greater than the mass of the reactants.