Multiple Choice
Given the bond energies: Br-Br = 192 kJ/mol, C≡C = 839 kJ/mol, C-Br = 276 kJ/mol, estimate ΔH°rxn for the reaction 2 Br2(l) + C2H2(g) → C2H2Br4(l). What is the ΔH°rxn?
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11. Bonding & Molecular Structure
Bond Energy
Multiple Choice
Use the bond energies to determine the approximate enthalpy change for the following reaction: H2(g) + 1/2 O2(g) → H2O(g). Given the bond energies: H-H = 436 kJ/mol, O=O = 498 kJ/mol, and O-H = 463 kJ/mol.
A
-146 kJ/mol
B
-184 kJ/mol
C
-326 kJ/mol
D
-242 kJ/mol
Verified step by step guidance1
Identify the bonds broken and formed in the reaction. In the reaction H2(g) + 1/2 O2(g) → H2O(g), the bonds broken are one H-H bond and half of an O=O bond. The bonds formed are two O-H bonds in H2O.
Calculate the energy required to break the bonds in the reactants. Use the bond energies provided: breaking one H-H bond requires 436 kJ/mol, and breaking half of an O=O bond requires 0.5 × 498 kJ/mol.
Calculate the energy released when new bonds are formed in the products. Forming two O-H bonds releases 2 × 463 kJ/mol.
Determine the enthalpy change of the reaction using the formula: ΔH = (energy required to break bonds) - (energy released from forming bonds).
Substitute the calculated values into the formula to find the approximate enthalpy change for the reaction.
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