Question

Which of the following reactions in the stratosphere cause an increase in temperature there? (a) \(\mathrm{O}(\mathrm{g})+\mathrm{O}_{2}(g) \longrightarrow \mathrm{O}_{3}{ }^{*}(\mathrm{~g})\) (b) \(\mathrm{O}_{3}^{*}(g)+\mathrm{M}(g) \longrightarrow \mathrm{O}_{3}(g)+\mathrm{M}^{*}(g)\) (c) \(\mathrm{O}_{2}(\mathrm{~g})+h \mathrm{w} \longrightarrow 2 \mathrm{O}(\mathrm{g})\) (d) \(\mathrm{O}(\mathrm{g})+\mathrm{N}_{2}(\mathrm{~g}) \longrightarrow \mathrm{NO}(\mathrm{g})+\mathrm{N}(\mathrm{g})\) (e) All of the above

Short answer

The short answer to the question is: (e) All of the above. Reactions (a), (b), and (d) involve the release of energy in the form of heat, which can increase the temperature of the stratosphere.

Step-by-step solution

Analyze each reaction

Identify the type and nature of each reaction, and if it would release or absorb energy. (a) O(g) + O2(g) → O3* (g) (b) O3*(g) + M(g) → O3(g) + M*(g) (c) O2(g) + hw → 2 O(g) (d) O(g) + N2(g) → NO(g) + N(g) (e) All of the above

Examine the formation of ozone

Reaction (a) involves the reaction of atomic oxygen (O) with molecular oxygen (O2) to produce ozone (O3). The * indicates that the ozone is in an excited state, which means the reaction has resulted in the release of energy stored in the excited ozone molecule.

Analyze the de-excitation of ozone

In reaction (b), the excited-state ozone (O3*) loses its excitation energy by transferring it to another molecule (M), forming ground-state ozone (O3) and an excited M molecule (M*). This energy transfer can increase the temperature of the stratosphere since the process releases energy in the form of heat.

Investigate the photodissociation of molecular oxygen

In reaction (c), molecular oxygen (O2) absorbs solar energy in the form of photons (hw) and dissociates into two atomic oxygen (O) species. In this reaction, energy is absorbed by O2 and not released, causing no direct increase in the stratospheric temperature.

Evaluate the reaction between atomic oxygen and molecular nitrogen

Reaction (d) consists of the reaction of atomic oxygen (O) with molecular nitrogen (N2), forming nitric oxide (NO) and atomic nitrogen (N). This reaction involves a bond formation in the NO molecule, which releases energy as heat, causing an increase in temperature.

Identify the correct option

Based on the analysis of reactions (a) to (d), reactions (a), (b), and (d) involve the release of energy in the form of heat, which can increase the temperature of the stratosphere. Hence, the correct option is (e) "All of the above", as it includes all the reactions that cause the increase in temperature in the stratosphere.

Key concepts

Ozone Formation Reaction

The formation of ozone in the stratosphere is a fascinating process with profound implications on atmospheric temperature. Ozone (O₃) is created when an oxygen atom (O) combines with molecular oxygen (O₂), often indicated in reactions as O(g) + O₂(g) → O₃. This reaction can occur in an excited state, denoted by an asterisk (O₃*), signifying that extra energy is stored within the ozone molecule.

This energy is what makes the ozone formation reaction impactful regarding temperature changes. When the excited ozone (O₃*) then converts to ground-state ozone (O₃), the excess energy is released. The dispersal of this energy in the form of heat increases the temperature of the surrounding stratospheric air, acting almost like a tiny furnace in our upper atmosphere. This process is a key component of the natural balance of atmospheric temperature and is essential for understanding Earth's radiation balance.

Excited State Molecules

When we speak of excited state molecules, we're referring to atoms or compounds that have absorbed energy and are, temporarily, in a higher energy state than their usual, or ground state. In the stratospheric temperature context, excited ozone molecules (O₃*) exemplify this concept quite well. These molecules possess excess vibrational, rotational, or electronic energy.

Interestingly, these molecules are like little packets of energy waiting to be released. When they return to their ground state, that stored energy is given off as heat, contributing to the warming of the stratosphere. Different reactions in the stratosphere, such as the de-excitation of O₃*, efficiently distribute the absorbed energy as heat, highlighting the significance of excited state molecules in atmospheric chemistry.

Photodissociation of Molecular Oxygen

Photodissociation is the process by which a chemical compound is broken down (dissociated) by photons, the elementary particles of light. Specifically, the photodissociation of molecular oxygen (O₂) plays a pivotal role in the stratospheric chemistry. The reaction is depicted as O₂(g) + hw → 2 O(g), representing the absorption of a photon by a molecular oxygen, which then splits into two separate oxygen atoms.

This process doesn't directly heat the stratosphere as it absorbs energy rather than releases it. However, the atomic oxygen produced is crucial for other reactions that do increase temperature, such as those leading to the formation of excited ozone. These reactions underscore the interconnected nature of stratospheric chemistry, where one reaction's products can fuel another, influencing the overall heat content of the atmosphere.

Chemical Reactions in the Stratosphere

Chemical reactions in the stratosphere are essential in understanding how different environmental processes affect Earth's climate. This high-altitude layer of the atmosphere is the site of complex interactions involving energy absorption, release, and the transformation of various gas species. Reactions like the creation of ozone and the production of nitric oxide (NO) from the reaction O(g) + N₂(g) are examples of exothermic processes where energy is emitted, contributing to stratospheric warming.

It's essential to examine each reaction to determine whether it will lead to a rise in temperature by assessing the energy changes involved. Reactions that release energy, particularly in the form of kinetic energy that translates to heat, play a part in raising the stratospheric temperature. Notably, these reactions are also influenced by factors such as solar radiation, season, and atmospheric composition, which can alter the rate and outcomes of the chemical processes taking place in this dynamic atmospheric layer.