4.1-4.3: Nitrogen Oxides, Ozone, and Gasoline: Flashcards
controlling factor (in chemistry of atmosphere/earth’s crust)
reactivity of oxygen
oxygen is avid for…
electrons (e-)
oxygen has the __ electronegativity
2nd highest
- (behind fluorine)
(oxygen) + (most elements) =
stable oxides
in Earth’s Crust = oxygen + _____ = oxides
Fe, Al, M, Ca, C, Si
in the ocean = oxygen + _____ = oxide
hydrogen
in the atmosphere = oxygen + ___ = oxides
CO2 and SO2
CO2 and SO2 oxides ( and nitrogen oxides) are…
highly volatile
Trends in atmospheric oxides are based on…
standard enthalpies & free energies of formation
Standard enthalpy
heat released/absorbed under standard conditions when compound is formed
exothermic
(-) = heat released
most molecules are…
exothermic
endothermic
(+) = heat absorbed
NO, NO2, O3 are all ___ molecules so…
endothermic
- free energy = (+)
standard conditions
- T = 25°C
- P = 1 atm
free energy is almost always __ and favors ___
(-) –> favors product formation at equilibrium
Free energy change =
ΔG = -RTln(Keq)
Keq =
equilibrium constant = ([products]^(# of molecules in reaction) ) /([reactants]^(# of molecules in reaction))
R =
gas constant = 0.008314 kJ K-1
T =
absolute temp = °K
Reaction ↑ heat =
favors product formation
- Equilibrium = shifted right
Standard thermodynamic equation for free energy =
ΔG = ΔH – TΔS
↓ temp =
reverse reaction (spontaneously)
Outside combustion zone, NO =
unstable = decomposition slows down
how are rates of reaction affected by temp?
↑ temp = ↑ rate of reaction
ΔG =
Δ in standard free energy of a reaction
hygroscopic
absorbed in rain-drops and rained into atmosphere
hygroscopic effect on NOx
Removes NOx molecules from atmosphere
Activation energy
kinetic barrier reaction must be overcome by energy input
Activation energy and free energy = dependent on ____
chemical and mechanism
gas-phase reactions are slow bc…
they require a higher activation energy
example of a mechanism for reaction
breaking reactant bonds, increasing temperature
Free radicals
involved in mechanisms for reactions (ex: HO⦁)
Hydroxyl radicals (HO⦁)
mechanism for atmospheric oxidation
How does the free energy of a reaction differ from the enthalpy of a reaction?
- Free energy- total energy available for thermodynamic work (enthalpy + entropy)
- Enthalpy- total energy of system that can be converted to heat
What does it mean when a free energy change is positive or negative?
(-) = releases energy ≠ energy input
- spontaneous
(+) = requires energy = energy input
- non-spontaneous
What is the relationship between the free energy change of a reaction and its equilibrium constant?
= inverse relationship
- ΔG = (+) –> Keq = (-)
- ΔG = (-) –> Keq = (+)
Reaction @ equilibrium: free energy =
0
What are the natural and anthropogenic sources of NO in the atmosphere?
- Natural: volcanoes, oceans, biological decay, lightning, microbial sources
- Anthropogenic: fossil fuel combustion, biomass burning, oxidation of ammonia
(-) enthalpy =
exothermic = heat released
(+) enthalpy =
endothermic = heat absorbed
