L7 - Gas phase chemistry Flashcards
(29 cards)
What are the primary components of dry air and their approximate percentages?
Nitrogen (78%), Oxygen (21%), Argon (0.934%), and Carbon Dioxide (0.04%)
How much water vapor is present in the atmosphere?
Between 0–3%, depending on temperature and location.
What units are used to express gas concentrations in the atmosphere?
Molecules per cubic centimeter (molecules cm⁻³)
What is Avogadro’s number, and how is it used in gas calculations?
Avogadro’s number is
6.02×10 ^23, used to convert moles to molecules
What is the ideal gas law and its significance in atmospheric chemistry?
P=nRT, which helps determine the number of molecules in a given volume under specific conditions
What is the molecular density of air at standard temperature and pressure (STP)?
2.7×10 ^19 molecules cm⁻³.
What does 1 ppm represent in gas concentration?
One molecule of gas per million molecules of air
How is 1 ppb different from 1 ppm?
1 ppb represents one molecule per billion (10⁹) molecules of air
What are unimolecular reactions?
Reactions involving the decomposition or rearrangement of a single molecule (e.g.,
A→B+C)
What are bimolecular reactions?
Reactions involving two reactants (e.g.,
A+B→C+D)
What are trimolecular reactions?
Reactions involving three reactants, often association reactions (e.g.,
A+B+M→AB+M)
What is the rate of reaction for a simple bimolecular reaction?
Rate=k[A][B], where
k is the rate coefficient
What are the units of the rate coefficient for a first-order reaction?
s ^-1
What are the units of the rate coefficient for a second-order reaction?
molecules
−1cm ^3 s ^−1
What are the units of the rate coefficient for a third-order reaction?
molecules ^−2cm ^6 ^−1
How is the chemical lifetime of a reactant defined?
The time it takes for a reactant to fall to
1/e of its original concentration
What is the equation for the chemical lifetime of a first-order reaction?
T=1/k A
How is the chemical lifetime of a second-order reaction calculated?
T=1/(k AB[B])
How is the chemical lifetime of a third-order reaction calculated?
T=1/(k ABM [B][M])
What is photochemistry?
The study of chemical reactions initiated by sunlight
What is photolysis?
The decomposition of molecules by the action of light.
Write the general equation for a photolysis reaction
A+hν→products
What is the rate equation for photolysis?
d[A]/dt=−J[A], where
J is the photolysis rate coefficient
What happens when NO₂ absorbs light with a wavelength less than 424 nm?
It photolyzes to form NO and O (NO2 + hν→NO+O)
