Question

. Calculate ∆H°rxn for each of the following:

(a) 2H2S(g) + 3O2(g) → 2SO2(g) + 2H2O (g)

(b) CH4(g) + CI2(g) → CCI4(l) + HCl(g) [unbalanced

Answer 1

(a) 2H₂S(g) + 3O₂(g) → 2SO₂(g) + 2H₂O (g)

Use the following equation to determine the standard heat of reaction

$∆H°_{rxn} = \sum m ∆H^°_f (products) - \sum n ∆H^°_f (reactants)$

m and n are the number of moles of products and reactants, respectively.

$∆H^°_f$ is the standard heat of formation.

$∆H^°_{rxn} = [2 \;mol \times (-296.8 \;kJ/mol) + 2 \;mol \times (-241.8 \;kJ/mol)] – [2 \;mol \times (-20.2 \;kJ/mol) + 3\; mol \times 0] \\ = [-593.6 \;kJ -483.6 \;kJ] -[-40.4 \;kJ] \\ = -1036.8 \;kJ$

(b) Balanced equation:

CH₄(g) + 4Cl₂(g) → CCl₄(l) + 4HCl(g)

$∆H^°_{rxn} = [1 \;mol \times (-139 \;kJ/mol) + 4 \times (-92.3 \;kJ/mol)] – [1 \;mol \times (-74.9\;kJ/mol) + 4 \;mol \times 0] \\ = [-139\; kJ -369.2 \;kJ] -[-74.9 \;kJ] \\ = -433 \;kJ$