Question

A mercury mirror forms inside a test tube by the thermal decomposition of mercury(II) oxide:

2HgO(s) => 2Hg(l) + O₂(g) ΔHrxn = 181.6 kJ

How much heat is needed to decompose 555 g of the oxide?

Answer 1

The amount of heat needed to decompose 555 g of mercury(II) oxide is approximately 232.7 kJ.

Step-by-step explanation:

The thermal decomposition reaction of mercury(II) oxide is represented by the equation: 2HgO(s) => 2Hg(l) + O₂(g).

The enthalpy change for this reaction, ΔHrxn, is 181.6 kJ.

To determine the amount of heat needed to decompose 555 g of mercury(II) oxide, we can use the equation:

1. Convert the mass of mercury(II) oxide to moles, using its molar mass of 216.59 g/mol. (555 g HgO) / (216.59 g/mol) = 2.562 mol HgO.
2. Since the reaction stoichiometry is 2 mol HgO to 1 mol O₂, we have 2.562 mol HgO * (1 mol O₂ / 2 mol HgO) = 1.281 mol O₂.
3. The amount of heat needed to decompose 1 mole of O₂ is 181.6 kJ, so the amount of heat needed to decompose 1.281 mol O₂ is 1.281 mol O₂ * 181.6 kJ/mol O₂ = 232.6776 kJ.

Therefore, the amount of heat needed to decompose 555 g of mercury(II) oxide is approximately 232.7 kJ.