No balance reads moles. Real problems hand you GRAMS, so the mole machine from chapter one runs first — $n = \dfrac{m}{M}$ — and only then does $q = n\,\Delta H$ collect its heat. Grams → moles → kilojoules: two small formulas, one chain, and the mole count is the coupling between them. The chain runs backwards too — a heat budget fixes the moles via $n = \dfrac{q}{\Delta H}$, and $m = n\,M$ dresses them in grams for the balance.

One trap gets a name here: the sign slip. An exothermic $\Delta H$ is negative, so q computes negative — heat leaving, exactly as it should. But when the ask says “heat released”, the answer is the MAGNITUDE: the word already spent the minus sign. Reporting −500 kJ released says the reaction absorbed it — the sign, spoken twice, flips the story.