Topscore 2 Chem #50 and #53

[clubwestpua]

50./
This question is about calculating bond energies of the reaction below.

2H2 + O2 --> 2 H2O

Bond Energy = Broken - Formed
It takes positive energy to break bonds, but when bonds form, energy is released, so I assumed that O-H bond energies must be converted to negative values. But the answer did not change signs for bond formation. Why??


53.

O3 <-- --> O2 + O (Fast)
O3 + O <-- --> 2 O2 (slow)

Why is it that the rate law is
Rate = k[O3][O]?

Isn't O an intermediate so it doesn't count??? Or am I just confused??

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[clubwestpua]

50.

Bonds broken - bonds formed equation already accounts for the exothermic bond formation with the minus sign

53.

The slow step is the rate of the reaction. Since O3 + O <-- --> 2 O2 (slow) is not a mechanism and is one elementary reaction then you can use the coefficients to form the rate law.

Thank you!!!