Regular flights of supersonic aircraft in the stratosphere are of concern because such aircraft produce nitric oxide, NO, as a byproduct in the exhaust of their engines. Nitric oxide reacts with ozone, and it has been suggested that this could contribute to depletion of the ozone layer. The reaction \(\mathrm{NO}+\mathrm{O}_{3} \longrightarrow \mathrm{NO}_{2}+\mathrm{O}_{2}\) is first order with respect to both \(\mathrm{NO}\) and \(\mathrm{O}_{3}\) with a rate constant of \(2.20 \times 10^{7} \mathrm{L} / \mathrm{mol} / \mathrm{s}\). What is the instantaneous rate of disappearance of NO when \([\mathrm{NO}]=3.3 \times 10^{-6} \mathrm{M}\) and \(\left[\mathrm{O}_{3}\right]=5.9 \times 10^{-7} \mathrm{M} ?\)

Rate law expressions are critical in understanding how chemical reactions proceed. In a reaction, each reactant can affect the overall rate differently. The general form of a rate law is rate = k[A]^{m}[B]^{n}...
, where k is the rate constant, [A] and [B] are the concentrations of the reactants, and m and n are the orders of the reaction with respect to each reactant. These orders are typically determined experimentally. In the case of the reaction between nitric oxide (NO) and ozone (O3), the reaction is first-order in both reactants, which means that the rate of reaction is directly proportional to the concentration of each one of them separately.

Understanding the rate law is not just about plugging in numbers; it involves recognizing how a change in concentration affects the rate. If we double the concentration of NO, for example, the rate of the reaction will also double, assuming that the concentration of O3 remains constant. This relationship is incredibly useful when predicting how varying conditions can affect the speed of a chemical reaction.

First-order reactions are a type of chemical reaction where the reaction rate is directly proportional to the concentration of one of the reactants. In mathematical terms, this is expressed as rate = k[A], where A is the reactant, and k is the first-order rate constant.

For a reaction that is first order with respect to a substance such as NO, the disappearance of NO over time follows an exponential decay pattern. This means that in equal time intervals, equal fractions of NO will react, regardless of the initial concentration. Understanding first-order kinetics helps in predicting how concentrations will change over time and is particularly relevant in processes such as radioactive decay or, in our context, the interaction of pollutants with atmospheric compounds. The comprehension of first-order reactions assists in modeling environmental concerns like ozone depletion, as well as understanding the pharmacokinetics of drugs in the body.

Ozone depletion refers to the thinning of the Earth's ozone layer, which is located in the lower portion of the stratosphere and is responsible for absorbing most of the harmful ultraviolet (UV) radiation from the sun.

Human activities have contributed to the depletion of the ozone layer, notably through the release of chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and related halogenated substances. Additionally, the reaction mentioned in our exercise, where NO from aircraft exhaust reacts with O3, highlights another path for ozone destruction. Ozone depletion has far-reaching consequences, including increased UV radiation reaching the Earth's surface, which can lead to skin cancer and cataracts in humans and harm wildlife, particularly marine ecosystems.

Interaction with NO and Ozone Layer

Understanding the chemistry behind NO's interaction with ozone is essential for grasping the impact of human activities on the ozone layer. In the given reaction, NO reacts with ozone to form NO2 and oxygen. This reaction reduces the O3 concentration, contributing to ozone layer depletion. The rate at which NO reacts with O3 in the stratosphere can be determined by the first order rate law expression and has implications for modeling the impacts of various forms of pollution on atmospheric chemistry and the health of the ozone layer.