Stratospheric Chemistry: The Ozone Layer
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Questions and Answers

What type of reactions are much slower in the atmosphere?

Endothermic reactions

What is the activation energy required for the reaction to be slow at stratospheric temperatures?

At least equal to 69 kJ mol^-1

What is the energy change (ΔH) for the reaction OH + HF -> H2O + F?

ΔH > 0

What is the energy difference for O* compared to ground-state atomic oxygen?

<p>190 kJ mol^-1</p> Signup and view all the answers

What is the energy difference for the abstraction from water of a hydrogen atom by ground-state atomic oxygen?

<p>69 kJ mol^-1</p> Signup and view all the answers

What type of reaction is the reaction of O* with H2O to give the same products?

<p>Exothermic</p> Signup and view all the answers

What is the ozone layer and why is it important?

<p>The ozone layer is a region of the atmosphere that filters out harmful ultraviolet (UV) rays from sunlight. It is important because it protects humans and other life forms from UV radiation.</p> Signup and view all the answers

What environmental crisis occurred in the mid-1980s related to the ozone layer?

<p>A large 'hole' in the ozone layer over Antarctica appeared, representing a major environmental crisis.</p> Signup and view all the answers

Why is the ozone hole a threat to life on Earth?

<p>Any substantial reduction in the amount of ozone would threaten life as we know it by allowing harmful UV rays to reach the surface and cause damage.</p> Signup and view all the answers

When does the ozone hole over Antarctica typically appear?

<p>The ozone hole over Antarctica typically appears each spring.</p> Signup and view all the answers

What is the significance of the large hole that occurred in the ozone layer in 2006?

<p>One of the largest holes in history occurred in 2006, highlighting the ongoing environmental challenge.</p> Signup and view all the answers

Why is it important to understand the natural chemistry of the ozone layer?

<p>Understanding the natural chemistry of the ozone layer is important to comprehend the processes at work in the ozone hole and the evolution of the hole.</p> Signup and view all the answers

What role do NO molecules play in the destruction of ozone?

<p>Extracting an oxygen atom from ozone and forming nitrogen dioxide</p> Signup and view all the answers

What is the overall reaction involved in the destruction of ozone by NO molecules?

<p>O3 -&gt; 2 O2</p> Signup and view all the answers

What is the rate law for the gas-phase reaction between nitric oxide and ozone?

<p>rate = k [NO] [O3]</p> Signup and view all the answers

What is the value of the rate constant, k, for the reaction between nitric oxide and ozone at an atmospheric temperature of about 50°C?

<p>6.5 x 10^-15 molecules^-1 cm3 sec^-1</p> Signup and view all the answers

How do NO molecules contribute to the formation of nitrogen dioxide in the reaction with ozone?

<p>By extracting an oxygen atom from ozone</p> Signup and view all the answers

Explain the significance of the reaction between nitric oxide and ozone in terms of atmospheric chemistry.

<p>This reaction contributes to the destruction of ozone, impacting the ozone layer and atmospheric composition.</p> Signup and view all the answers

What is the overall reaction of Mechanism II involving ozone molecules?

<p>2 O3 --&gt; 3 O2</p> Signup and view all the answers

What is the significance of a species shown in square brackets in chemistry?

<p>It indicates a species with a transient existence.</p> Signup and view all the answers

What must either X or X be in Mechanism II?

<p>A chlorine atom</p> Signup and view all the answers

What happens to the catalysts X and X in Mechanism II after the reaction steps?

<p>They are ultimately regenerated</p> Signup and view all the answers

What is the role of UV light in the production and destruction of ozone?

<p>UV light is essential for the production of ozone from oxygen</p> Signup and view all the answers

What is the main cause of ozone loss in the lower stratosphere?

<p>Mechanism II</p> Signup and view all the answers

What are the three gases that constitute most of the Earth's atmosphere?

<p>Nitrogen, Oxygen, Argon</p> Signup and view all the answers

What is the range of altitudes that constitutes the troposphere?

<p>0-12 km</p> Signup and view all the answers

What is the range of altitudes that constitutes the stratosphere?

<p>12-50 km</p> Signup and view all the answers

What is the primary atmospheric gas responsible for filtering sunlight in the 120-220 nm region?

<p>Ozone</p> Signup and view all the answers

What is the wavelength range for visible light? Does ultraviolet light have shorter or longer wavelengths than visible light?

<p>Visible light ranges from 400-700 nm. Ultraviolet light has shorter wavelengths than visible light.</p> Signup and view all the answers

Write the equation for the chemical reaction by which ozone is formed in the stratosphere. What are the sources for the different forms of oxygen used as reactants?

<p>O2 + O -&gt; O3; Molecular oxygen (O2) and atomic oxygen (O) are the sources for the reactants.</p> Signup and view all the answers

What are the equations relating photon energy E to light's frequency ν and wavelength λ?

<p>E = hν = hc/λ</p> Signup and view all the answers

What are the two reactions that contribute most significantly to ozone destruction in the stratosphere, aside from catalyzed reactions?

<p>O3 + O -&gt; 2O2; O3 + UV light -&gt; O2 + O</p> Signup and view all the answers

What is meant by the term 'excited state' as applied to an atom or molecule? How is an excited state symbolized?

<p>An 'excited state' is a state in which an atom or molecule has absorbed energy and moved to a higher energy level. It is symbolized by an asterisk (*) next to the chemical symbol.</p> Signup and view all the answers

Explain why the phrase 'ozone layer' is a misnomer.

<p>The ozone layer is not a distinct layer but a region with varying concentrations of ozone. It is not a separate, well-defined layer.</p> Signup and view all the answers

Define the term 'free radical' and provide two examples relevant to stratospheric chemistry.

<p>A free radical is a highly reactive species with an unpaired electron. Examples in stratospheric chemistry include hydroxyl radical (OH•) and nitric oxide (NO).</p> Signup and view all the answers

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