Question

A mercury mirror forms inside a test tube as a result of the thermal decomposition of mercury(II) oxide: 2 HgO(s) → 2 Hg(l) + O2(g) ΔHrxn = 181.6

(a) How much heat is needed to decompose 571 g of the oxide?

(b) If 844 kJ of heat is absorbed, how many grams of Hg form? × 10 g Hg (Enter your answer in scientific notation.)

Answer 1

2 HgO(s) → 2 Hg(l) + O₂(g) ΔH_rxn = 181.6 kJ

2 moles of HgO decomposes to give 2 moles of Hg by taking 181.6 kJ energy

2x 216.6 (433.2 grams) of HgO decomposes to give 2 x 200.6 (401.2 grams) of Hg by taking 181.6 kJ energy

(a) Heat is needed to decompose 571 g of the oxide

   433.2 grams of HgO decomposes by taking 181.6 kJ energy

   571 grams of HgO decomposes by taking ---- ? energy = (571/433.2) x 181.6 = 239.37 kJ

(b) Amount of Hg formed when 844 kJ of heat is absorbed by HgO

181.6 kJ of heat absorbed to give 401.2 grams of Hg

   844 kJ of heat absorbed to give ----- ? grams of Hg = (844/181.6) x 401.2 = 1864.6 grams = 1.8646 x 10³ grams