Final answer:
The missing 0.5 grams in the chemical reaction could have been released as energy or in an uncollected form like gas or heat, according to the Law of Conservation of Mass.
Step-by-step explanation:
When mixing 5 grams of substance A with 3 grams of substance B and only 7.5 grams of a new substance is formed, with 0.5 grams seemingly missing, the Law of Conservation of Mass may suggest that the 'lost' mass was released into the environment as energy or in a form that was not collected, such as gas or heat.
This is a common occurrence in chemical reactions, especially when reactions are exothermic and involve combustion. An example is the combustion of isopropyl alcohol, where the missing mass corresponds to the oxygen atoms originally present in the reactants.