Speaking in generalities yes, but TECHNICALLY stuff that contains more energy is heavier too. But given that most enthalpies are in the kJ/mole range and most

Speaking in generalities yes, but TECHNICALLY stuff that contains more energy is heavier too. But given that most enthalpies are in the kJ/mole range and most moles of things are pretty heavy relative to 9e18 (the speed of light squared) that you might as well round it out and say "no mass is created or destroyed in an ordinary chemical reaction"