regions of the atmopshere and activation enegry and collion theory
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What are the two broad divisions of the atmosphere in the lecture
The lower atmosphere and the upper atmosphere.
What does the lower atmosphere include
The troposphere and stratosphere.
Approximately how high does the lower atmosphere extend
To approximately 50 km.
What does the upper atmosphere include
The mesosphere, thermosphere, and exosphere.
How are atmospheric regions differentiated
By their temperature profiles.
What are the four main atmospheric layers
Troposphere, stratosphere, mesosphere, and thermosphere, followed by the exosphere.
What is the troposphere
The lowest atmospheric layer, extending from Earth's surface to approximately 10–15 km.
How does temperature change with altitude in the troposphere
Temperature decreases with altitude.
What is the approximate temperature gradient in the troposphere
Approximately 1°C decrease per 100 m.
Why does temperature decrease with altitude in the troposphere
Expansion cooling occurs as air rises into regions of lower pressure.
What is expansion cooling
Cooling that occurs when a gas expands as its surrounding pressure decreases.
What type of vertical mixing occurs in the troposphere
Strong and rapid vertical mixing.
Why does the troposphere experience strong vertical mixing
Warm air rises while cooler air sinks.
What is the stratosphere
The atmospheric layer above the troposphere, extending to approximately 45–55 km.
What are the lower and upper boundaries of the stratosphere
The tropopause and stratopause.
How does temperature change with altitude in the stratosphere
Temperature increases with altitude.
Why does temperature increase with altitude in the stratosphere
Heat is released during ozone formation.
What is the temperature inversion in the stratosphere
The increase in temperature with increasing altitude.
How does vertical mixing occur in the stratosphere
Mixing is relatively slow and inefficient.
Why is vertical mixing slow in the stratosphere
The temperature inversion limits the movement of air between different altitudes.
What is the mesosphere
The atmospheric layer above the stratosphere, extending approximately from 50–85 km.
How does temperature change with altitude in the mesosphere
Temperature decreases with altitude.
What is the mesopause
The boundary between the mesosphere and thermosphere.
What is the coldest point in the atmosphere
The mesopause.
How does vertical mixing occur in the mesosphere
Vertical mixing is relatively fast.
What is the thermosphere
The atmospheric region above the mesosphere.
How does temperature change with altitude in the thermosphere
Temperature increases with altitude.
Why does temperature increase in the thermosphere
Oxygen and nitrogen absorb short-wavelength radiation.
What is the exosphere
The outermost region of Earth's atmosphere, located above approximately 400 km.
What happens to gas molecules in the exosphere
Some molecules have enough energy to escape Earth's gravitational pull.
What are atmospheric transition zones
Boundaries between atmospheric layers where the temperature gradient is approximately zero.
What is the tropopause
The boundary between the troposphere and stratosphere.
What is the stratopause
The boundary between the stratosphere and mesosphere.
What is the mesopause
The boundary between the mesosphere and thermosphere.
What is the thermopause
The boundary between the thermosphere and exosphere.
What does dT/dH = 0 represent
A point where temperature does not change with altitude, marking a transition between atmospheric layers.
What is the temperature trend through the atmospheric layers
Temperature decreases in the troposphere, increases in the stratosphere, decreases in the mesosphere, and increases in the thermosphere.
What is collision theory
The idea that atoms, molecules, or ions must collide for a chemical reaction to occur.
What determines whether a collision produces a reaction
The particles must collide with sufficient energy and suitable orientation.
How does temperature affect reaction rates according to collision theory
Increasing temperature increases the number of collisions with sufficient energy to react.
How does concentration affect reaction rates
Increasing reactant concentration generally increases the frequency of collisions.
What is activation energy (Ea)
The minimum energy required for colliding reactants to form products.
Why is activation energy required
Existing bonds must be broken or rearranged before new bonds can form.
What happens when reactants collide with insufficient energy
They do not overcome the activation energy barrier and generally do not react.
What happens when reactants collide with sufficient energy
They can overcome the activation energy barrier and form products.
What is an example reaction used to illustrate bond rearrangement in the lecture
Cl + NOCl → Cl₂ + NO.
What happens during a chemical reaction at the molecular level
Bonds in reactants are broken and new bonds form to produce products.
What is a reaction mechanism
A series of elementary reactions that describe how an overall chemical reaction occurs.
What is an elementary reaction
A single reaction step that cannot be broken down into simpler reaction steps.
What is an overall reaction
The net chemical reaction obtained by adding the elementary steps together.
What is an intermediate
A chemical species produced in one reaction step and consumed in a later step.
What happens to intermediates when elementary reactions are added together
They cancel because they are produced and then consumed.
What must the sum of elementary steps equal
The overall chemical reaction.
What is the rate-determining step
The slowest elementary step in a reaction mechanism.
Why is the rate-determining step important
It limits the overall reaction rate.
What must a valid reaction mechanism agree with
The stoichiometry of the overall reaction and the experimentally determined rate law.