Question

Joseph Priestly prepared oxygen in 1774 by heating red mercury(II) oxide with sunlight focused through a lens. How much heat is required to decompose exactly 1 mole of red HgO(s) to Hg(l) and O2(g) under standard conditions?

a) 90.9 kJ
b) 135 kJ
c) 180 kJ
d) 257 kJ

Answer 1

The heat required to decompose 1 mole of red mercury(II) oxide into liquid mercury and oxygen gas under standard conditions is 257 kJ.

Step-by-step explanation:

The decomposition of red mercury(II) oxide (HgO) to form liquid mercury (Hg) and oxygen gas (O2) requires a certain amount of heat.

To calculate the heat required, we need to use the standard enthalpy of formation values for each species involved.

The balanced equation for the reaction is 2HgO(s) -> 2Hg(l) + O2(g). The standard enthalpy change of this reaction is 257 kJ/mol, which means that 257 kJ of heat is required to decompose exactly 1 mole of red HgO(s) under standard conditions.