CHEM 051 Exam 1

Environmental spheres

Lithosphere: solid earth
Hydrosphere: water
Biosphere: all life
Atmosphere: gases/air

Pollutants

Chemicals that have an adverse environmental or ecological impact

Atmosphere

troposphere (where we live, 75% mass) → stratosphere → (ozone layer) mesosphere → thermosphere → exosphere

temp fluctuations, lower pressure = air is thinner, colder temp

How are chemicals classified

1) phase of matter (how tightly matter is packed together — solid, liquid, gas)
2) composition (what are they made of? — element, compound, mixture)

Mixture

Matter that does not have constant properties and composition

Heterogenous mixture

Mixture that is not uniform throughout (ex: trail mix)

Homogenous mixture

Mixture that is uniform throughout (ex: coffee, air)

Pure substance

Matter that has constant properties and composition / can write a singular chemical formula for it

Element

Pure substance that cannot be simplified chemically (ex: silver (Ag), diamonds/graphite (C))

Compound

Pure substance that can be simplified chemically (ex: table salt (NaCl), water (H₂O))

Groups

Columns on the periodic table, contain elements with similar properties

Periods

Rows on the periodic table, chemical properties evolve systematically

Molecular compounds

compounds composed of 2 or more nonmetals (such as CO₂ or CO)

Naming molecular compounds

1) name each element in chemical formula (element further to the left on periodic table goes first)
2) modify suffix of second element to end in “-ide”
3) use prefixes to indicate ratio based on formula (not mono for first element if 1)
ex: CO₂ = carbon dioxide

Molecular compound prefixes

1	mono-	6	hexa-
2	di-	7	hepta-
3	tri-	8	octa-
4	tetra-	9	nona-
5	penta-	10	deca-

Classifying air pollutants

1) source: anthropogenic or natural, primary (directly emitted) or secondary (formed in atmospheric chemical reactions)

2) composition: what molecules are there, in what proportions, etc

Clean Air Act 1970

Requires EPA to set National Ambient Air Quality Standards for 6 pollutants “The Dangerous Few” (NAAQS) (carbon monoxide, sulfur dioxide, lead, ozone, nitrogen oxides, particulate matter)

Carbon monoxide

(CO)

• binds to hemoglobin more strongly than oxygen

• source: combustion byproduct

Sulfur dioxide

(SO₂)

• dissolves in lungs to form an acid, causes acid rain

• source: fossil fuel combustion, volcanoes

Lead

(Pb)

• systemic toxicant

• source: waste incineration, mining, (a long time ago, gasoline)

Ozone

(O₃)

• reduces lung function

• source: chemical reactions

Nitrogen oxides

(NO_x)

• class of chemicals

• dissolves in lungs to form an acid

• source: combustion byproduct, especially cars

Particulate matter

• solids or liquids trapped in the air

• lung irritant

• classified by size, not chemical composition

• wide range of sources

Risk assessment

Different levels and time scales set for regulation based upon the various toxicity and level of exposure for each air pollutant.

hazard/risk = toxicity x exposure

Toxicity: intrinsic health hazard of substance
Exposure: amount of substance encountered

Chemical reactions

A process by which one or more substances are converted to another. Atoms are never created or destroyed, total mass must be conserved.

Reactant → product

Combustion Reactions

Very formulaic

hydrocarbon + oxygen → carbon dioxide + water

also releases energy as heat and light

Hydrocarbon

Chemical compound made of just hydrogen and carbon (sometimes oxygen), named by # of carbon atoms in structure. Includes many fuels (gas, oil, natural gas)

Hydrocarbon prefixes

1	meth-	6	hex-
2	eth-	7	hept-
3	prop-	8	oct-
4	but-	9	non-
5	pent-	10	dec-

Saturated hydrocarbon

Carbon always makes 4 bonds, all 4 bonds from C area made to H or another C (Cn H2n + 2) Have “-ane” suffix (ex: methane CH₄)

Balancing combustion reactions

1. write chemical reaction

2. balance carbon atoms

3. balance hydrogen atoms

4. balance oxygen atoms

5. double check and make sure all coefficients are whole numbers

What atom goes in middle of depictions / is central atom

The least electronegative atom is always the central atom (but never hydrogen). Flourine (F) is most electronegative so furthest from F are least on periodic table, Francium (Fr) is least

Complete combustion

if oxygen is ample, safer reaction: C_x H_y (l) + O₂ (g) → CO₂ (g) + H₂O (g)

Incomplete combustion

favored in low O₂ conditions, pollutant byproducts, less safe

Gasoline combustion

Complete: 2 C₈H₁₈ (l) + 25 O₂ (g) → 16 CO₂ (g) + 18 H₂O (g)

Incomplete: 2 C₈H₁₈ (l) + 17 O₂ (g) → 16 CO (g) + 18 H₂O (g)

CO₂ is less toxic than CO so complete combustion is safer

Additives

allow us to preferentially choose the safer reaction by adding in oxygen in forms other than O₂ (oxygenizing) ex: MTBE

Impurities

some other chemical in fuel that is not intentionally added, give rise to other pollutants (ex: sulfur is an especially pervasive impurity in coal, also combusts when fuel burns reacts with O₂ to form SO₂ ), we refine fuels to reduce impurities so they burn cleaner

Catalytic converters

work to remove NO_x from gas-powered car emissions, plate made of expensive metals (rhodium, platinum, palladium), use surface chemistry through surface of metals to drive pollutant-removing reactions

Air

Collection of gases mixed together in various proportions throughout the atmosphere “mixture”

pure substances in air: nitrogen, oxygen, argon, carbon dioxide, water

Composition of air

78% nitrogen (N₂), 21% oxygen (O₂), 1% other gases

Parts per million

Measurement for trace substances, % = parts per hundred

ppm = 1/1,000,000

Coal burning smog

historical smog / london smog

2 SO₂ (g) + O₂ (g) → 2 SO₃ (l)

sulfuric acid gives rise to aerosols - generates particulate matter which causes smog

SO₃ (l) + H₂O (l) → H₂SO₄ (l)

Aerosols / particulate matter

generated by sulfuric acid, particulate matter scatters light instead of transmitting light, creates a hazy look and is harmful to breathe in, cause smog

Photochemical smog

• LA smog — primary emissions VOCs, geography of basin traps pollution, temperature inversion

needs sunlight to produce, brown haze

when VOCs are present ozone builds up

NO₂ + sunlight → NO + O

O + O₂ → O₃

O₃ + NO → NO₂ + O₂

hydroxyl radical

unpaired electron, very reactant, unstable

C₈H₁₈ + . OH

peroxy radical

diverts NO from usual course of action (removing O₃) and generates NO₂ leading to more ozone, can continue to react over and over creating more hydrocarbons, ozone buildup

C₈H₁₈ + . OH → H₂O + . C₈H₁₇ — octyl radical

. C₈H₁₇ + O₂ → . C₈H₁₇O₂ — peroxy radical

. C₈H₁₇O₂ + NO → . C₈H₁₇O + NO₂

diurnal variation

air pollution varies throughout the day, worst 1-5pm, sun has been up + cars rush hour

Stratospheric ozone

protects earth from solar radiation, acts as a blanket from the sun, “bad down here, good up there”

Wavelength

λ lambda, the distance between peaks in a wave reported in units of length (m)

inversely proportional to energy

Frequency

v nu, how many waves pass a fixed point in a certain amount of time (1/s or s^-1 Hertz (Hz) inverse second)

Relationship between wavelength and frequency

λv = c

Inversely proportional

long λ = lower v, short λ = higher v

c

speed of light

c = 3.00 × 10⁸ m/s

Photons

particles of light

quantum

groups of photons / packets of energy

energy

E photon = hv

E— energy of one photon in joules

Planck’s constant

h = 6.63 × 10^-34 J x s

Spectrum of electromagnetic radiation

type	gamma	x-ray	ultraviolet	infrared	terahertz	microwave	broadcast wireless	radio
λ	10-3	10-1	10	103	105	107	109	1011
v	1020	1018	1016	1014	1012	1010	108	106

microwave radiation

causes rotation of molecules, low energy and light

infrared radiation

makes bonds in molecules vibrate

ultraviolet radiation

breaks bonds in molecules (ex O₃, NO₂), high energy

three types: UV-A not as harmful in short term, UV-B bad with exposure over time, UV-C causes rapid harm — ozone layer blocks some UV (5% A, 95% B, 100% C)

Chapman cycle

null cycle of production and destruction of ozone in the stratosphere, keeps at stable level

O₂ + hv (λ < 280 nm) → O + O — production

O + O₂ + M → O₃ + M (M is placeholder for a third body maybe N or O)

O₃ + hv (λ < 320nm) → O + O₂ — destruction

O + O₃ → 2 O₂

The ozone hole

Thinning of ozone layer, especially over antarctica, human activity can introduce contaminants to the stratosphere

catalytic destruction of ozone by nitrogen oxides, repeating cycle

NO + O₃ → NO₂ + O₂

NO₂ + O → NO + O₂

net: O + O₃ → 2 O₂

catalytic destruction of ozone by chlorine radicals

Chlorine radicals

come from CFCs and other stuff, aerosols and refrigerants

CFC + hv → . Cl

. Cl + O₃ → . ClO + O₂

. ClO + O → . Cl + O₂

net: O + O₃ → 2 O₂

CFC replacements

HCFCs, HFCs, HFOs, PFAS

Atomic structure

Nucleus: center part of atom, contains most mass
Protons: +1
Neutrons: neutral (inside nucleus)

Electrons (outside of nucleus) -1

Elemental properties

All atoms of one element have same # of protons in nucleus

• # of protons = atomic number (z)

• # of protons + # of neutrons = mass number (A)

• for a neutral atom → # of electrons = # of protons

Isotopes

atoms with the same # of protons but different # of neutrons

valence electrons

electrons on outermost shell (each group has same #)

Electrons

dictate where things are located on the periodic table, most stable in pairs

lone pairs

electron pairs localized on an atom (not shared)

bonding pairs

electron pairs found in the space between atoms (shared), can be double or triple and become harder to break and more stable

octet rule

atoms strive towards 8 valence e-

lewis structures

visual depictions of where valence e- are around an atom

lewis structures of molecules

1. sum up all valence electrons (for all atoms present in molecule)

2. connect atoms with bonds (1 bond = 2 electrons)

3. distribute remaining electrons

resonance

more than one lewis structure can be equally valid for a molecule (ex: ozone), actual struture is an average of the resonant structures

electron domains

places where electrons can be on the central atom

keeling curve

CO₂ levels rising over time, seasonal variations

Greenhouse effect

of incoming solar radiation, some absorbed by clouds + atmosphere, some reflected, 48% absorbed by earths surface, some reflected

of absorbed, some goes back into space as infrared radiation, gases in atmosphere absorb this trapping heat

Greenhouse gases

Molecules are a GHG if they absorb IR

VSEPR

(valence shell electron pair repulsion theory)

model for 3D structure of molecule, count domains around central atom (each lone pair or bonding area)

# electron domains	shape	angle
2	linear	180
3	trigonal planar	120
4	tetrahedral	109.5
5	trigonal bipyramidal	90 and 120
6	octahedral	90

what makes a molecule absorb IR light?

The distribution of charge (electrons) in the molecule must change as the molecule vibrates

Asses:

1. draw lewis structure

2. use VSEPR to think in 3D

3. think about what would happen if bonds stretch/bend
   → asymmetric stretching, bending

Dipoles

Arrow that shows how electrons are shared in a molecule

Carbon cycle

Carbon gets stuck in and stays in lithosphere, hydrosphere, and biosphere (progressively shorter residence time), moves in and out of atmosphere

Reservoirs

places where carbon is stored for a long time (all spheres except atmosphere)

Source

Process that moves carbon from reservoir into accessible form (some sphere → atmosphere)

Sink

Process that stores carbon in a reservoir (atmosphere → some sphere)

Pre-industrial carbon cycle

lithosphere → atmosphere = volcanoes

atmosphere → lithosphere = rock weathering + carbonate burial

biosphere → atmosphere = respiration, decomposition

atmosphere → biosphere = photosynthesis

hydrosphere → atmosphere = off-gasing of CO₂ from ocean

atmosphere → hydrosphere = CO₂ dissolving in ocean

all cancels out — no buildup of carbon in any one sphere

Post-industrial carbon cycle

• ocean uptake (atmosphere → hydrosphere)

• land use change / deforestation (biosphere → atmosphere)

• fossil fuel combustion (lithosphere → atmosphere)

• enhanced photosynthesis / land uptake (atmosphere → biosphere)

Future changes

• permafrost thaw, melting releases gases and allows decomp (hydro/bio → atmosphere)

• more soil respiration (litho/bio → atmosphere)

• reduced ocean uptake of CO₂ (decreases sink, harder to dissolve with warmer temp)

• wildfire increases (bio→ atmosphere)

Mole

(mol), small measurement for atoms, 1 mole of anything = 6.02 × 10²³ of those things / Avogadro’s Number

Avogadro’s Number

(N_A) # of things in a mole, = 6.02 × 10²³

Molar mass

unique relationship between moles and mass for every substance, shown on periodic table at bottom of each element

Global Warming Potential

(GWP) the warming induced by 1 kg of a gas compared to 1 kg of CO₂

1. how many different wavelengths of IR does gas absorb? → higher total # of atoms in molecule = more ways to vibrate = more λs absorbed

2. how strongly does the gas absorb IR? → higher # of electronegative atoms = stronger absorption (F)

3. how long does gas last in atmosphere? → short lifetimes = C=C (carbon double bonds) or H atoms

Aerosol Direct Effect

incoming sunlight is reflected or absorbed by particulates/aerosols:

light scattering — occurs if particle is light colored = cooling

absorption — occurs if particle is dark colored = warming

sulfate-centered droplets scatter more light

Aerosol Indirect Effect

particles help clouds form, make clouds more stable/last longer, and make clouds whiter and more reflective = overall net cooling

Positive feedback

speeds up warming (self-reinforced)

increasing temps = less snow/ice = less light reflected out to space = more light absorbed by darker land = higher temps

increased temp = ice melts = methane in permafrost released = higher temps

Negative feedback

slows down warming

increasing temps = more water vapor = more cloud formation = more light reflected back out to space = cooling