6. At elevated temperatures, NO2 undergoes decomposition in the gas phase, forming NO and O2 as repr — Kinetics, Lewis Structures, VSEPR Theory Chemistry Question
Problem Context
6. At elevated temperatures, NO2 undergoes decomposition in the gas phase, forming NO and O2 as represented by the following equation.
2 NO2 → 2 NO + O2
A scientist measures the change in [NO2] over the first 100. s of the reaction at 546°C. The scientist uses the data collected from the experiment to generate the following two graphs.
Based on these data, the scientist makes the claim that the rate law for the reaction is rate = k[NO2]^2.
(a) Explain how the graphs indicate that the reaction is second order with respect to NO2.
Model Answer
The plot of 1/[NO₂] versus time is the most linear, indicating that
the reaction is second order with respect to NO₂ [1, 2].
(b) At a certain point in the reaction, the rate of disappearance of NO2 is determined to be 6.52 × 10^-7 M/s. Determine the rate of appearance, in M/s, of O2 at this same point in the reaction.
Model Answer
6.52 × 10⁻⁷ *M*/s × (1 mol O₂ / 2 mol NO₂) = 3.26 × 10⁻⁷ *M*/s [2].
(c) NO2 is a molecule that contains an odd number of electrons and can be oxidized to form the NO2+ ion. In NO2, the unpaired electron is presumed to be localized on the nitrogen atom, as shown in the Lewis diagram in the box on the left.
(i) In the box on the right, complete the Lewis diagram for NO2+. Be sure to show all bonding and nonbonding electrons.
Model Answer
[ :O=N=O: ]⁺
*(Note: The expected Lewis diagram shows a central N atom double-bonded to two O
atoms. Each O atom has two lone pairs of electrons. The entire molecule is
enclosed in brackets with a + sign outside to indicate the positive charge)* [1,
2].
(ii) A student makes the claim that the bond angles in NO2 and NO2+ are different from each other. Do you agree or disagree with the student’s claim? Justify your answer.
Model Answer
Accept one of the following valid justifications:
* Agree. The angle of NO₂⁺ is different from the angle in NO₂ because there
would no longer be a nonbonding electron on the central atom in NO₂, and the O
atoms would spread farther apart, forming a linear structure with a 180° bond
angle [2, 3].
* Agree. The hybridization of N in NO₂ is *sp²*, which would result in a bond
angle of approximately 120°. The hybridization of N in NO₂⁺ is *sp*, which would
result in a bond angle of 180° [2, 3].
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