Two compounds exist apart and are stable. They have a certain "chemical potential" or potential energy. When two compounds are combined and the products, the assumed products for this reaction to be at a lower chemical potential, this would indicate that the reaction is exothermic since the potential energy of the products lie lower that that of the reactants.
An analogy for a covalent bond to form it has to more stable and at lower chemical potential than the bonds that are being broken.
If you were on top of the Empire State building and looked over the edge (assuming fear of heights or vertigo) you would feel quite uneasy at this height or potential energy. Now place yourself at the bottom of the same building and look down, not as far to fall, you fell more at ease, more stable; and you would have less potential energy to work with since all you can do is fall to the ground ( several ft.) The reaction analogy is that you felt unstable, high potential energy; you walked to the bottom and felt more stable with less potential energy.
An analogy for a covalent bond to form it has to more stable and at lower chemical potential than the bonds that are being broken.
If you were on top of the Empire State building and looked over the edge (assuming fear of heights or vertigo) you would feel quite uneasy at this height or potential energy. Now place yourself at the bottom of the same building and look down, not as far to fall, you fell more at ease, more stable; and you would have less potential energy to work with since all you can do is fall to the ground ( several ft.) The reaction analogy is that you felt unstable, high potential energy; you walked to the bottom and felt more stable with less potential energy.