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Multiple Choice
Use the bond energies to estimate the enthalpy of reaction for the combustion of 5 moles of acetylene:
A
-1074 kJ
B
2685 kJ
C
-2685 kJ
D
-430 kJ
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1
Identify the bonds broken in the reactants: In 2 moles of C2H2, there are 2 C≡C bonds and 4 C-H bonds. In 5 moles of O2, there are 5 O=O bonds.
Calculate the total energy required to break these bonds using the bond energies: (2 moles of C≡C * 839 kJ/mol) + (4 moles of C-H * 413 kJ/mol) + (5 moles of O=O * 498 kJ/mol).
Identify the bonds formed in the products: In 4 moles of CO2, there are 8 C=O bonds. In 2 moles of H2O, there are 4 O-H bonds.
Calculate the total energy released by forming these bonds using the bond energies: (8 moles of C=O * 745 kJ/mol) + (4 moles of O-H * 467 kJ/mol).
Estimate the enthalpy change of the reaction by subtracting the total energy of bonds formed from the total energy of bonds broken: ΔH = (Energy of bonds broken) - (Energy of bonds formed).