A table with 2 columns and 3 rows. Column 1 is labeled Reaction Equation with entries Reaction 1: Upper M g (s) + 2 Upper H Upper C l (a q) right arrow Upper M g Upper C l Subscript 2 (a q) + Upper H Subscript 2 Baseline (g); Reaction 2: Upper M g (s) + 2 Upper H Upper C l (a q) right arrow Upper M g Upper C l Subscript 2 Baseline (a q) + Upper H Subscript 2 Baseline Upper O (l); Reaction 3: Upper H Subscript 2 Baseline (g) + one half Upper O Subscript 2 Baseline (g) right arrow Upper H Subscript 2 Baseline Upper O (l). Column 2 is labeled delta H in kilojoules per mol with entries negative 450, negative 81, negative 286.Reaction(s) released heat. Reaction released the most heat per mole of reactant.