Answer the following questions about ozone. — Kinetics Chemistry Question
Problem Context
Answer the following questions about ozone.
Model Answer
1 point is earned for a diagram that includes all 18 valence electrons and obeys the octet rule.
1 point is earned for showing correct application of resonance.
Model Answer
The ozone molecule has a bent shape.
1 point is earned for the shape based on student's Lewis diagram.
Model Answer
ΔH° = Σ (bond enthalpies)_reactants - Σ (bond enthalpies)_products
Four equivalent bonds are broken in two O3 molecules. Three oxygen-oxygen double bonds are formed in three O2 molecules.
Let x = the bond enthalpy in ozone, therefore
4x - 3(498 kJ/mol) = -285 kJ/mol_rxn
4x - 1494 = -285
4x = 1209
x = 302 kJ/mol
1 point is earned for the correct determination of the number of bonds broken in the reactants and the number of bonds formed in the products.
1 point is earned for the calculation of the energy of the bonds in O3 consistent with bond counting, the bond energy of O2, and the ΔH°_rxn.
Model Answer
(i) Half-life = 0.010 s
1 point is earned for the correct answer.
(ii) t_1/2 = 0.693 / k1 ⇒ k1 = 0.693 / t_1/2 = 0.693 / 0.010 s = 69 s^-1
1 point is earned for the correct value.
1 point is earned for the correct unit.
(iii) The data are consistent with rate = k2 [O3][HSO3^-] because [HSO3^-] remains essentially constant during the experiment. ([HSO3^-] can be contained in the rate constant k1.)
1 point is earned for a correct explanation.
(iv) Repeat the experiment with a different initial concentration of HSO3^-. (If the change in the rate of the reaction is directly proportional to the change in [HSO3^-], then the reaction is first order with respect to HSO3^-.)
1 point is earned for describing a valid experiment.