For the balanced chemical equation: 2C2H6(g) + 7O2(g) → 4CO2(g) + 6H2O(g), what is the standard enthalpy change (ΔH°) for the reaction using the standard heats of formation?

• A. -1800 kJ/mol
• B. -1560 kJ/mol
• C. -1400 kJ/mol
• D. -1200 kJ/mol

Answer: (B)

Verified step by step guidance

1. Identify the balanced chemical equation: 2C₂H₆(g) + 7O₂(g) → 4CO₂(g) + 6H₂O(g). This equation shows the reactants and products involved in the reaction.
2. Understand that the standard enthalpy change (ΔH°) for the reaction can be calculated using the standard heats of formation (ΔH_f°) of the reactants and products. The formula is: ΔH° = ΣΔH_f°(products) - ΣΔH_f°(reactants).
3. Look up the standard heats of formation for each compound involved in the reaction. These values are typically found in tables in chemistry textbooks or reliable online resources. For example, ΔH_f° for CO₂(g) and H₂O(g) are commonly known values.
4. Calculate the total standard heat of formation for the products: 4CO₂(g) and 6H₂O(g). Use the formula: ΣΔH_f°(products) = 4 × ΔH_f°(CO₂) + 6 × ΔH_f°(H₂O).
5. Calculate the total standard heat of formation for the reactants: 2C₂H₆(g) and 7O₂(g). Use the formula: ΣΔH_f°(reactants) = 2 × ΔH_f°(C₂H₆) + 7 × ΔH_f°(O₂). Note that the standard heat of formation for O₂(g) is zero because it is in its elemental form.