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) → Arxn - 287 kJ If 113 kJ of heat is absorbed, how many grams of Hg form? (Note: 102 g Hg).

a) 91.15 g Hg
b) 101.54 g Hg
c) 82.08 g Hg
d) 92.73 g Hg

Answer 1

To find the mass of Hg that forms, divide the heat absorbed by the enthalpy change of the reaction. Multiply the moles of Hg by the molar mass of Hg to find the mass of Hg formed.

Step-by-step explanation:

To determine the mass of Hg that forms, you first need to calculate the moles of HgO that decompose. From the balanced chemical equation, you can see that 2 moles of HgO produce 2 moles of Hg. To find the moles of Hg formed, divide the heat absorbed (113 kJ) by the enthalpy change of the reaction (-287 kJ/mol). This gives you the moles of Hg formed. Finally, multiply the moles of Hg by the molar mass of Hg (102 g/mol) to find the mass of Hg formed.

Step-by-step calculation:

1. Determine moles of HgO decomposed: 113 kJ / (-287 kJ/mol) = 0.3935 mol
2. Determine moles of Hg formed (1:1 ratio): 0.3935 mol
3. Calculate mass of Hg formed: 0.3935 mol × 102 g/mol = 40.05 g