Exam 2 Review PDF

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The second portion reviewed on in my Summer 1 Chemistry Class. ...

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Exam 2 Review – Chapters 2 & 3 (CHEM 1305, Summer I 2019)

 Chapter 2 o Layers of the Atmosphere  Troposphere (0-11km)  Layer closest to the Earth  Contains 75% of the atmosphere  Stratosphere (11-48km)  Contains the ozone layer at an altitude of 15-35km  Mesosphere (48-95km)  Thermosphere (90-550km)  Exosphere (>550km) o Average Ozone Concentration Troposphere Stratosphere

20-100ppb ~12000ppb

o Balancing Chemical Reactions/Equations  Step 1: Look for elements that appear in only one reactant & only one product!  Balance them first!  Step 2: If free, uncombined elements appear on either side of chemical equation:  Balance them last!  NEVER ALTER FORMULAS (change subscripts)  Only adjust coefficients to balance the equation o Hydrocarbons (HC)  A compound containing only hydrogen and carbon  Examples: CH4 (Methane), C3H8 (Propane), C8H18 (Octane) o Types of Combustion  Complete Combustion  Reacts Oxygen with an HC to produce CO2 and H2O o Occurs with enough O2 present o Complete Combustion of Octane Chemical Equation  2C8H18 + 25O2 -> 16CO2 + 18H2O  Incomplete Combustion  Reacts O2 with an HC to produce CO and H2O o Occurs with insufficient O2 present o Incomplete Combustion of Octane

 2C8H18 + 17O2 -> 16CO + 18H2O o Gasoline  A complex mixture of HCs & other organic compounds  Car exhaust is a major source of CO  Since 1980, the average atmospheric pressure of CO in the US has gone down 60%  Why? o Cars have been improved to promote better fuel-oxygen mixtures  More complete combustion o All cars manufactured since mid-1970s have catalytic converters o Catalytic Converters  Functions of Catalytic Converters  Lowers CO emissions o Converts CO -> CO2  Lowers NOx emissions o Converts NOx -> N2 + O2 o Average CO Concentration  35ppm  35 Molecules of CO/1 x 106 molecules air  Average breath of Air  1.34 x 1022 molecules air/500 mL  Number of CO molecules allowed in one breath  4.7 x 1017 molecules CO/breath o Production and accumulation of atmospheric ozone  Ozone is a secondary pollutant  I.E. Lightning  Produced from chemical reactions involving other pollutants  Starts with a photochemical reaction o 1- NO2 -sunlight-> NO + O o 2- O + O2 -> O3 (ozone)  O3 is a major component of photochemical smog  High levels of O3 are common in cities o Indoor air  Volatile Organic Compounds (VOCs)  Organic compounds that evaporate rapidly  More of a problem with indoor atmospheres  Some VOCs are pollutants and accumulate indoors  Examples of VOCs: o Nicotine o Benzene

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o Formaldehyde o Ammonia o Acetone o Butanal  Sources of VOCs: o Smoking/Vaping o Cleaning Products o Painting o Wood Burning Stoves/Fireplaces o Candles o Air Fresheners o Nail Polish o Moth Balls  Chemically unreactive pollutants are more dangerous than reactive pollutants because they linger in the air longer Radon  Naturally occurring indoor pollutant  Colorless/Odorless/Tasteless  Formed from the radioactive decay of uranium o Uranium is found in small amounts in most rocks (~4ppm) o Many construction materials (rock & minerals) contain uranium  Bricks  Concrete/Cement  Stone/Tile  Cinderblock  Granite  Marble  Problem with Radon o Radioactive and a Noble Gas  Poses biggest health risk in basements o When Rn decays it forms other radioactive elements that are solids  Stick to dust and lung tissue if inhaled o Rn is the second-leading cause of Lung Cancer worldwide behind tobacco smoke

 Chapter 3 o Electromagnetic spectrum

o Photons  Particles of light composed only of energy that has no mass o E = hc/l  h= Planck’s Constant  c= Speed of Light (constant) 3.00 x 108 m/s  E increases/decreases as l decreases/increases o Biological effects of UV radiation  Green plants absorb red light/photons to carry out photosynthesis

o Factors Affecting UV Exposure and Skin Damage  1- Latitude: UV Exposure increases at lower latitudes because sun rays travel through less atmosphere and are very filtered.  2- Altitude: UV Exposure increases at higher altitudes because atmosphere has less chance to absorb incoming UV.  3- Stratospheric Ozone: Decreases in stratosphere ozone increases UV exposure.  4- Tanning Beds- Increase UV Exposure. o Valence Electrons  Outermost electrons involved in chemical bonding o Covalent Bonds  Involve the sharing of electrons between atoms o Lewis Structures

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1- 1 pair of electrons – single bond 2- 2 pairs of electrons – double bond 3- 3 pairs of electrons – triple bond The Octet Rule  Noble Gases contain 8 VE o Exception: He only contains 2 VE  All nonmetals like to have 8 valence electrons around them like the noble gases o Exception: H only likes 2 electrons like He  Lewis structures of molecules must contain an octet of electrons around each atom o Exception: H only needs 2 electrons Equation: SP = ½(ER-VE)  SP= Number of shared pairs  ER= Number of electrons required to equal 8 o (# of atoms other than H) (8e-) +(# H atoms) (2e-)  VE= Number of Valence Electrons available from each group – sum from group numbers The following atoms prefer the corresponding number of shared pairs of electrons in molecules:  (See notebook) Rules for Drawing Lewis Structures  1- Solve Equation: SP=1/2(ER-VE)  2- Choose reasonable geometry o Least electronegative element is usually central atom (EXCEPT H) o H only forms ONE BOND  3- Connect all atoms with single bonds o Add double or triple bonds to satisfy the number of shared pairs if necessary o Add lone pairs of atoms electrons to complete each atom’s octet- EXCEPT FOR H.  LEWIS STRUCTURES MUST SHOW ALL VALENCE E-S!...