Question

Calculate the DH°rxn for the decomposition of calcium carbonate to calcium oxide and carbon dioxide. DH°f [CaCO3(s)] = –1206.9 kJ/mol; DH°f [CaO(s)] = –635.1 kJ/mol; DH°f [CO2(g)] = –393.5 kJ/mol CaCO3(s) --> CaO(s) + CO2(g)

Answer 1

Answer:

ΔHrxn for this reaction is  178.3 kJ/mol

Explanation:

Step 1: Data given

ΔH°f [CaCO3(s)] = –1206.9 kJ/mol

ΔH°f [CaO(s)] = –635.1 kJ/mol

ΔH°f [CO2(g)] = –393.5 kJ/mol

Step 2: The balance equation

CaCO3(s) --> CaO(s) + CO2(g)

Step 3: Calculate ΔHrxn

ΔHrxn = The sum of ΔHf of the products - ΔHf of the reactants

ΔHrxn = ((-393.5 kJ/mol) + (-635.1 kj/mol)) - (-1206.9 kJ/mol)

ΔHrxn = 178.3 kJ/mol

ΔHrxn for this reaction is  178.3 kJ/mol

Answer 2

Answer:

ΔHrxn = 178.3 kJ/mol

Explanation:

Using Hess's law, you can obtain ΔHrxn from ΔHf of products and reactants, thus:

Hess's law:

ΔHrxn = ∑nΔHf products - ∑nΔHf reactants

Where n are moles of reaction

Thus, from the reaction:

CaCO₃(s) → CaO(s) + CO₂(g)

ΔHrxn = ΔHf CaO(s) + ΔHf CO₂(g) - ΔHf CaCO₃(s)

ΔHrxn = -635.1kJ/mol + (-393.5kJ/mol) - (-1206.9kJ/mol)

ΔHrxn = 178.3 kJ/mol