A mercury mirror forms inside a test tube by the thermal decomposition of mercury(II) oxide. 2 HgO(s) 2 Hg(l) + O2(g) Hrxn = 181.6 kJ (a) How much heat is needed to decompose 504 g of the oxide? kJ? (b) If 282 kJ of heat is absorbed, how many grams of mercury form? g?