Thermochemical Stoichiometry

Question

1) The following thermochemical equation is for the reaction of bromine trifluoride(g) to form bromine(g) and fluorine(g).

2BrF₃(g) Br₂(g) + 3F₂(g)    H = 542 kJ

How many grams of BrF₃(g) would be made to react if 104 kJ of energy were provided?

2) The following thermochemical equation is for the reaction of hydrogen sulfide(g) with water(l) to form hydrogen(g) and sulfur dioxide(g).

H₂S(g) + 2H₂O(g)3H₂(g) + SO₂(g)    H = 207 kJ

When 8.11 grams of hydrogen sulfide(g) react with excess water(l), ____ kJ of energy are _________(evolved/absorbed).

Hint: An amount of energy is expressed as a positive number. The sign of ΔH in the thermochemical equation indicates whether the energy is absorbed or evolved.

Answer 1

1)

104kJ x 2 mol BrF₃ / 542 kJ x 137g BrF₃ / mol BrF₃ = 52.6g BrF₃

2)

8.11g H₂S x mol H₂S / 34.08g H₂S x 207kJ/mol H₂S = 49.3 kJ

Positve energy value means energy is absorbed.