Use bond energies to calculate ? H rxn for the reaction. 2H2( g )+O2( g )?2H2O(

Question

Use bond energies to calculate ?Hrxn for the reaction.

2H2(g)+O2(g)?2H2O(g)

Note: The answer is NOT 442 kJ or 442kJ/mol

It gave me this hint when I got the answer wrong: The bond energies of H?H, O=O, and H?O are provided in the introduction. To determine the enthalpy of this reaction, sum all of the bond energies for the reactants (accounting for stoichiometric ratios as is), and subtract the bond energies for the product. Note how many bonds are in each molecule.

HW 11 CH 9 (9.7-9.9 For More Practice 9.11 with feedback Resources previous l 14 of 29 l next For More Practice 9.11 with feedback Part A Average Bond Energies Use bond energies to calculate AH for the reaction Bond Energy Bond 2H2(g) O2 (g) 2H2O(g) (kJ/mol) Express your answer as an integer and include the appropriate units 436 498 464 You may want to reference (D ages 365 370 Section 9.10 while completing this problem. AHL Submit My Answers Give Up incorrect; Try Again; 3 attempts remaining Provide Feedback Continue

Explanation / Answer

reactant has:
2 H-H bond
1 O=O bond

product has:
4 O-H bond

H = BE (product) - BE (reactant)
= 2*BE (H-H) + 1*BE (O=O) - 4*BE (O-H)
= 2*(436) + 1*(498) - 4*(464)
= -486 KJ/mol

Answer: -486 KJ/mol

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