Chemistry - SCH3U - Unit 6 - Gases and Atmospheric Chemistry - Note

Part 1: KMT, Atmosphere, Air quality

States matter

  • Solid

    • Defined shape and volume

    • Virtually incompressible

    • Does not flow easily

    • Strong force attraction between entities

  • Liquid

    • Take shape of container but has definite volume

    • Slightly compressible

    • Flows readily

    • Medium force of attraction between entities

  • Gas

    • Take shape and volume of container

    • Highly compressible

    • Flows readily

    • Low force of attraction between entities

Kinetic molecular theory

  • Robert Brown 1773 - 1858

    • Examine pollen speck suspend water and found pollen move at random

    • Brownian motion

      • Random movement of microscopic particle suspended in liquid/gas

  • Kinetic molecular theory

    • Develop from scientific interpretation of Brown observation

    • Entities in solid, liquid, gas are in constant motion

      • As move they collide other object in path

      • Kinetic = come from greek work kinema (mean constant motion)

      • Kinetic energy = energy of moving object

How entities move

  • Transitional motion

    • Movement of entity along linear path

    • Liquid and gas

  • Rotational motion

    • Spinning of entity in place

    • Liquid and gas

    • Very limited in solid

  • Vibrational motion

    • Back and forth vibration of entity

    • Solid and liquid and gas

Kinetic energy and temperature

  • When substances warmed entities move more rapidly

    • Fast entity move = more kinetic energy

  • Temperature = measure of average kinetic energy of entity in substance

    • Thermometer work from entity of substance collide with thermometer so energy transfer liquid in thermometer cause expand

  • As more energy transfer in solid it vibrate faster

    • Eventually attractive force broken which allow entity flow past

      • Change state solid to liquid

  • Warming liquid increase kinetic energy of entity

    • Eventually attractive force completely overcome

      • Liquid boil and change state to gas

Atmosphere

  • Atmosphere = thin blanket moisture and gas that protect Earth from outer space environment

    • Mostly concentrated first 100km of Earth surface

    • Stabalize surface temperature which make Earth habitable

    • Most dense surface Earth

      • Molecule in air pushed together by atmosphere above

        • Atmosphere less dense with higher altitude

Atmosphere layer

  • Troposphere

    • Closest Earth surface

    • Warmest near Earth surface

      • Temperature decrease with altitude

    • Solar energy absorb by Earth transfered to air molecule as thermal energy

    • Air movement determine weather

  • Stratosphere

    • Dry region with higher then normal concentration ozone

      • Ozone has ability trap ultraviolet radiation of sun

        • Trapped energy release gas molecule with increase kinetic energy

    • Temperature increase with altitude

    • Due to increase of kinetic energy

  • Mesosphere

    • Extend 50km - 85km

    • Low gas concentration

    • Contain little ozon

    • Temperature decrease with altitude

  • Thermosphere/ionosphere

    • Extend beyond 85km

    • Gas molecule absorb solar radiation to become ionized

      • Will emit visible radiation (auroras)

      • Warms thermosphere

    • Auroras particularily over polar region

      • Also called aurora borealis, northern lights, aurora austrialis, southern lights

Composition of atmosphere

  • Troposphere and stratosphere have biggest influence

  • Nitrogen (N_2 )

    • Most abundant gas in atmosphere

    • Important all biological system

    • Cycle Earth through nitrogen cycle

      • Nitrogen fixing bacteria convert nitrogen gas into soluble nitrate

        • Soluble nitrate = form plant can easily absorb through roots

      • Nitrogen release back atmosphere from body decay plant and animal and waster

  • Oxygen (O_2 ) and ozone (O_3 )

    • Make up 21% of atmosphere

    • Required for cellular respiration

    • Most ozone in atmosphere concentrate in statosphere

    • Ozone absorb UV light effectively making it radiation shielf

      • Prevent excessive UV read Earth surface

    • Ozone also found troposphere where it is air pollutant and key ingredient in smog

  • Other gases

    • Argon, water vapour, carbon dioxide make majority remain gas in atmosphere

    • Argon = colourless, odourless, chemically inert

    • Water vapour = 1% - 3% in atmosphere

      • Over 99% of all water vapour in troposphere in water cycle

    • Carbon dioxide only 0.036% of lower atmosphere

      • But essential for life on Earth

      • Returned to atmosphere by living organism

        • From waster product of cellular respiration

Greenhouse effect and climate change

  • Atmosphere help keep Earth surface warm by trap thermal energy from ground

  • Without atmosphere Earth average temperature = -18°C

  • With atmosphere Earth average temperature = 15°C and rising

  • How atmosphere keep Earth warm

    • Atmosphere is transpart to higher energy radiation of sun

    • Much of radiation absorb by Earth suface and transform thermal energy

    • Warm object on Earth surface give off energy as lower energy infrared (IR) radiation

  • Greenhouse gas (GHG) = gas in atmosphere that trap infrared radiation

    • Trapped IR contribute greenhouse effect

    • Most important GHG

      • Carbon dioxide, methane, water vapour

    • Less significant GHG

      • Nitrous oxide, fluorinated gas

    • Specific frequencies of IR cause greenhouse gas to vibrate

      • As vibrates reradiates energy

        • Some sent back Earth surfact which warms ground

    • Greenhouse effect = process of trap infrared radiation within atmosphere

  • Concnetrations of greenhouse gass fluctuation over time

    • Higher concentration correspond period high global temperature

      • Volcanic emmision, continental drift, change in solar energy, change in ocean circulation, large meteor strike

  • Human activity over last 200 year cause significant increase GHG in atmosphere

  • Climate change cause

    • Change water level

    • Dsitrupt ecosystem

    • Less sea ice and degration of permafrost

Reducing GHG emissions

  • Enforce emission standard fir vehicle

  • Provide fund to farmer and business to invest environmentally friendly practices

  • Recycling and reusing

  • Driving less, public transportation, car pooling

  • Insulating, cauking, weather stripping

  • Carbon sequestration = remove carbon dioxide from atmosphere and store it

    • Biological sequestration

      • Plants used to naturally sequece/remove carbon dioxide

    • Geological sequestration

      • Capture and store carbon dioxide in grand deposit

      • Has cost

        • May leak

          • Negatively affect environment

        • Expensive

F.K. Hore

  • Born Englad 1919

  • Wrote and spoke extensively to raise awarness to issue relate climate change

  • Won many award for effort

Air quality

  • Smog = complex mixture air pollutant mostly from human activity

  • Photochemical smog

    • Experienced in many city

    • Contain ground levelo ozone, gases, fine particles

    • Produce by reaction of vehicle and factory emission with sunlight

    • Prefix “photo“ = light

    • Appear as brown haze

  • Exposure smog cause eye and heart iritation, aggravate pre-exist repiratory issue

  • Particulate matter, gases, volatile organic compound contribute poor air quality

Particulate matter

  • Particulate matter = mixture solid and liquid particle in atmsosphere

  • Size can range few molecule to visible dust particle

  • Almost all combustion reaction produce some aprticulate matter

  • Can damage respiratory system

  • Reduce visibility and threaten air travel

Pollutant gases

  • Sulfur dioxide (SO_2 )

    • Clear, colourless gas with strong choking odor

    • Most of this gas produce by combustion of fossil fuel with sulfur impurity

    • Contribute to acid precipitation

    • Can cause respritory irritation, stimulate mucus production, loud wheeze, short of breath

    • People with preexisting respiratory issues are especially susceptible

  • Nitrogen oxides (NO, No_2 , N_2O_4 )

    • Brownish smog result nitrogen dioxide

    • Other nitrogen oxide

      • Nitrogen monoxide

      • Dinitrogen tetroxide

    • Most nitrogen oxide emission result of vehicle use fossil fuel

    • Contribute toa cide precipitation

  • Carbon monoxide (CO)

    • Colourless, odourless, gas that toxic high concentration

    • Incomplete combustion produce carbon monoxide and pure carbon

    • Concentration carbon monoxide higher 25ppm can affect long term health

  • Volatile organic compound (VOC)

    • Solid or liquid carbon-contain compound that vaporize readily

    • Many naturally occur

    • Eg

      • Gasoline vapour, pine tree odour, aerosol spray, paint, air freshener, dry clean clothes, wood perservative, clean solvent

    • Symptom VOC exposer

      • eye iritation, head ache, rash

      • Depress central nervous system, cause cancer

  • Ozone

    • Powerful bleach

      • Very corrosive

    • Produce from reaction of nitrogen oxide and VOC in sunlight

    • Equations

      • Fuel burn in air at high temperature

        • N_2 (g) + O_2 (g) → 2NO (g)

      • Colourless nitrogen monoxide form reddish brown pollutant nitrogen dioxide

        • 2NO (g)(colourless) + O_2 → 2NO_2 (g)(reddish brown)

      • Nitrogen dioxide react UV radiation

        • NO_2 (g) → (UV) NO (g) + O (g)

      • Oxygen by self to reactive so react with oxygen compound to form ozone

        • O (g) + O_2 (g) → O_3  

    • VOC not directy involve form ozone

      • But help form nitrogen dioxide which form ozone

    • Concentration ozone peak when sunlight most intense

Air quality health index

  • Environemtn Canada develop Air Quality Helath Index (AQHI)

    • Based on health risk for level of common air pollutant

      • Ozone, particulate matter, nitrogen dioxide

    • Caterogy

      • 1-3

        • Low risk

      • 4-6

        • Moderate risk

      • 7-10

        • High risk

      • 10+

        • Very high risk

Part 2: Pressure, Boyle's Law, Charles' Law, Gay-Lussac's Law, & Combined Gas Law - Note

Pressure

  • Pressure = force per unit area

  • Physical property of gas

  • Equation

    • P = F/A

    • Pressure = force/area

  • Smaller area higher pressure

  • Larger area lower pressure

  • SI unit for pressure is pascal

    • 1 Pa = 1 N/m²

      • 1 pascal = 1 newton/meter squared

Atmospheric pressure

  • Atmospheric pressure

    • Force per unit area exerted by air on all object

      • Commonly report use kilopascal (kPa)

  • Standard pressure

    • Pressure exert by air base 1m² at sea level equal to 101.325 kPa

  • Standard temperature and pressure (STP)

    • Gases at temperature 0°C and pressure 101.325 kPa

  • Standard ambient temperature and pressure (SATP)

    • Gases at temperature 25°C and pressure 100 kPa

    • Since 0°C not convenient temperature conduct laboratory investigation

      • SATP more convenient then STP since more closely represent condition of laboratory

Evangelista Torricelli (1608-1674)

  • First person devise method measure atmospheric pressure

  • Problem

    • Pump in Tuscany cannot raise water more 10m when use suction pump

  • Solution

    • Use mercury (denser then water) to investigate

    • Fill long glass tube with mercury, invert (upside down), submerge into dish filled with mercury

  • Observations

    • Mercury in tube pull down from gravity

    • Did not completly drain from air, pressure push mercury in tube

    • Vaccum form top of tube

      • Vaccum exert no downward pressure on mercury inside tube

    • Mercury level in tube change day to day from change in air pressure

  • Result

    • Device called barometer

    • At one time standard pressure define as 760 mm Hg or 760 Torr

      • Torr in honour Torricelli

SI and non SI units of pressure

  • Pascal (Pa)

    • 1 Pa = 1 N/m²

  • Kilopascal (kPa)

    • 1kPa = 1000 Pa

  • Millimetre mercury (mm Hg)

    • 760 mm HG = atm = 101.325 kPa

    • Used to measure blood pressure

  • Torr (Torr)

    • 1 Torr = 1mm Hg

  • Atmosphere (atm)

    • 1 atm = 101.325 kPa (exactly)

  • Pounds per square inch (psi)

    • 1 psi = 6895 Pa

    • Used to measure tire pressure

Atmospheric pressure and altitude

  • Density gas in atmosphere change with altitude

    • Density decrease as altitude increase

      • Lower gas density mean less collision per unit area and lower pressure

    • Density increase as altitude decrease

      • Higher gas density mean more collision per unit area and higher pressure

      • Atmospheric pressure most dense at sea level

  • Ear hurt from quick change altitude

    • Cause by change atmospheric pressure from quick change altitude

    • Middle ear

      • Air filled chamber that isolated from outside air by eardrum

      • Connected to eustachian tube

    • When gain altitude

      • Atmospheric pressure decrease

      • With less pressure on eardrum volume gas in middle ear increase which push eardrum out

      • Cause uncomfortable feeling of fullness in ear

    • Relief

      • Make eustachian tube open up allowing air flow middle ear to throat

        • Qualize pressure of air in middle ear to atmospheric pressure

      • Chew gum, yawn, swallow

  • Railway tank air designed withstand pressure higher inside then outside

    • If pressure inside tank lower then outside atmospheric pressure crush tank

High altitude training

  • Endurance athlete train high altitude at attempt improve performance

  • Generally go elevation above 2000 m where air pressure 77-80 kPa

    • Still 21% oxygen in air but all atmospheric gas lower density

      • Lower density mean each breath contain less oxygen then sea level

  • After 3-4 week body compensate lower oxygen level

    • Make more red blood cell to carry oxygen and produce more enzyme to utilize oxygen

  • After return lower altitude feel energize and increase ability use oxygen

  • Disapointing performance result cannot train as rigorously while adjust higher altitude and lower oxygen level

  • Some athlete live high altitude and train low

    • Obtain physiological advantage of higher altitude but still train intensively

Celsius scale/centrigrade scale

  • Develop by Swedish scientist Anders Celsius in 1742

    • Devise by enclose tube pure liquid, such as mercury

    • Record height liquid when place ice water

      • This height called 100 degree

    • Record height liquid when placed boiling water

      • This height called 0 degree

    • Divided distance 0-100 degree exactly 100 division

  • Scale later reversed for more practical unit measure

  • Centigrade = divide into 100 degree

Absolute value and temperture scale

  • Lord kelvin first notice value every gas equal zero at -273.15°C

  • Absolute value = lowest possible temperature

    • -273.15°C

  • Kelvin temperature scale set absolute value to 0 of new scale

  • Unit symbol k

Charles law

  • How popcorn

    • Popcorn non porous shell and small quantity water trap inside

    • When kernal heated water becomes gas (water vapour)

    • Water vapour explains in kernal eventually burst

  • Jacque Charles (1746-1823)

    • French scientist

  • Volume gas increase as temperature increase

    • Graph straight line volume against temperature

  • As gas cooled eventually condense to liquid

    • Cannot measure temperature for gas in this state

  • Law state volume of gas proportional to temperature in kevins

    • If pressure and amount gas constant

  • Equation

    • V = aT

      • a = constant

      • T = absolute temperature (in kevins)

    • V/T = a

    • V_1 / T_1 = V_2 / T_2

      • Ratio same

  • At molecular level

    • As temperature increase kinetic energy of gas entity increase

    • Higher kinetic energy entity move more quickly and more collision between entities

    • Number of collision between entities and wall of container increase

      • Make container expand and increase volume of gas

  • Jacque Charles = balloon enthusiast

    • Experiment hydrogen gas hot air balloon

    • Generate hydrogen by react large quantity acid and iron

    • 1783 one balloon travel Paris to outskirt city in 45m

      • Local resident attack and destroy

How breathing work

  • When inhale diaphragm contract and rib cage expand

  • Allow more volume for lung and create lower pressure

  • Air move area low pressure into lung

  • When exhale diaphragm expand and rib cage contract

  • Decrease volume for lung and create higher pressure

Boyles law

  • Robert Boyle

    • British scientist

  • Law state as volume gas decrease the pressure of gas increases proportionally

    • If temperature and amount gas constant

  • Graph volume vs pressure = curve

  • Graph volume vs 1/pressure = straight line

  • Contain inverse property

  • Equation

    • PV = h

      • P = pressure

      • V = volume

      • k = constant

    • P_1 V_1 = P_2 V_2

Gay-Lussacs law

  • Law state pressure of gas increase proportionally as temperature increase

  • Equation

    • PT = k

    • P_1 / T_1 = P_2 / T_2

Combined gas law

  • Charles law equation

    • V/T = constant (n and P controlled)

  • Boyles law equation

    • PV = constant (n and T controlled)

  • Gay-Lussacs law equation

    • P/T = constant (n and V controlled)

  • Combined gas law equation

    • PV/T = constant

  • Describes relationship between volume, temperature, pressure any fixed gas

    • Constant as long as amount gas constant