Chemistry - SCH3U - Unit 6 - Gases and Atmospheric Chemistry

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