Use the information provided to determine ΔH°_rxn for the following reaction: ΔH°_f (kJ/mol) CH₄(g) + 4 Cl₂(g) → CCl₄(g) + 4 HCl(g) ΔH°_rxn= ?
CH₄(g) -75
CCl₄(g) -96
HCl(g) -92

Question

Quizplus · Accepted Answer

Using Hess's Law, ΔH°S1U1B1rxnS1U1B0 can be calculated by subtracting the sum of the standard enthalpies of formation of the reactants from the sum of the standard enthalpies of formation of the products:

ΔH°S1U1B1rxnS1U1B0 = [ΔH°S1U1B1f(CClS1U1B14S1U1B0(g)) + 4ΔH°S1U1B1f(HCl(g))] - [ΔH°S1U1B1f(CHS1U1B14S1U1B0(g)) + 4ΔH°S1U1B1f(ClS1U1B12S1U1B0(g))]

Plugging in the given values:
ΔH°S1U1B1rxnS1U1B0 = [(-96 kJ/mol) + 4(-92 kJ/mol)] - [(-75 kJ/mol) + 4(0 kJ/mol)]
ΔH°S1U1B1rxnS1U1B0 = (-464 kJ/mol) - (-75 kJ/mol)
ΔH°S1U1B1rxnS1U1B0 = -389 kJ/mol

Therefore, the answer is choice A, with an explanation using Hess's Law.

Use the Information Provided to Determine ΔH°rxn for the Following

Use the Information Provided to Determine ΔH°_rxn for the Following