chemistry ch 18-22 chemistry in a sustainable world

• composition of clean air: 78% nitrogen, 21% oxygen, 0.96% noble gases mainly argon, water vapour and other gases, 0.04% carbon dioxide
• uses of gases: (1) nitrogen: boiling point (-196 °c) - considered as an inert gas as its triple bond is relatively strong and hard to break - reactions involving nitrogen as a reactant have relatively high activation energies
• uses of gases:

  (2) oxygen: boiling point (-183 °c)

  • essential for combustion
  • used to support patients with breathing difficulties
  • used as oxidiser in welding that joins pieces of metals together strongly
• uses of gases:

  (3) argon: boiling point (-186 °c)

  • provide inert environment for high temperature processes (e.g. in lightbulbs and thermal purification of copper and steel) - separation of liquid air: fractional distillation, since nitrogen has the lowest boiling point, it is boiled off and collected first
• air pollution is the introduction of unwanted and harmful chemicals into the atmosphere
• (air pollutants & harmful effects) 1. sulfur dioxide: colourless and pungent odour

  • cause: combustion of fossil fuels and volcanic eruptions 2. nitrogen oxide: NO- colourless and odourless, NO2- red brown, pungent smell
  • cause: vehicle combustion engines and lighting
  • effect: SO2 causes breathing difficulties in humans and animals, sulfur dioxide and nitrogen oxides react with oxygen to form acidic compounds which dissolves in rain water to form acid rain. --> it kills plants and aquatic life, corrodes building and structures made from limestone, marble and metal
• (air pollutants & harmful effects) 3. carbon monoxide: colourless and odourless, very toxic

  • cause: incomplete combustion of carbon-based fuels
  • effect: binds irreversibly with haemoglobin--> less oxygen transported around the body --> loss of consciousness and death
• (air pollutants & harmful effects) 4. methane: colourless and odourless, highly flammable

  • cause: anaerobic bacterial decay of organic substances and waste gases from cattle
  • effect: major greenhouse gas which causes global warming
• (air pollutants & harmful effects)

  5. unburnt hydrocarbons (CxHy): colourless and naturally odourless, may be pungent due to fuel additives

  • cause: vehicle combustion engines
  • effect: eye and respiratory tract irritation, reacts with nitrogen oxide in presence of sunlight to form smog (brown haze) --> smog produces ozone, SO2 and NO2
• (air pollutants & harmful effects) 6. ozone: pale blue gas, pungent odour

  • cause: lighting, reactions between oxygen and sunlight in upper atmosphere, reaction between unburnt hydrocarbons and nitrogen oxides in presence of sunlight in lower atmosphere
  • effect: eye and respiratory tract irritation, breathing difficulties, chest pains, headache, slows down photosynthesis --> damage crops
• acid rain:

  • leaches magnesium and calcium from the soil which hampers health and growth of trees
  • decreases the pH of soil, kills species
  • water acidification --> less biodiverse in water bodies
• (control of air pollution) 1. catalytic converters: installed midway in the exhaust system of a vehicle between the engine and the muffler

  (redox reactions)

  • carbon monoxide (2CO) + nitrogen monoxide (2NO) → carbon dioxide (2CO2) + nitrogen (N2)
  • carbon monoxide (2CO) + oxygen (O2) → carbon dioxide (2CO2)
  • nitrogen dioxide (2NO2) → nitrogen (N2) + oxygen (2O2)
  • octane (2C8H18) + oxygen (25O2) → carbon dioxide (16CO2) + water vapour (18H2O)
• (control of air pollution)

  2) flue gas desulfurisation: removes a significant proportion of SO2 from flue gas produced from waste incinerators

  • wet scrubbing (CaCO3 mixed with water to form slurry)
  • CaCO3 (s) + SO2 (g) → CaSO3 (s) + CO2 (g)
  • (calcium sulfite further oxidised to form calcium sulfate) 2CaSO3 (s) + O2 (g) → 2CaSO4 (s)
  • (calcium sulfate hydrated - known as gypsum) CaSO4 (s) + 2H2O (l) → 2CaSO4 . 2H2O (s)
• gypsum (hydrated calcium sulfate) is used to make drywall, fertilisers, plaster for sculptures and casts that stabilise fractured bones. It is essential in making tofu
• (control of air pollution)

  (3) low sulfur fuels: in vehicles

  • excess sulfur can be removed from fossil fuels by treating it with hydrogen gas producing hydrogen sulfide
• (control of air pollution)

  (4) liming

  • carbonate is added to soil and water bodies to remove excess acid from the acid rain
  • however, this process is expensive and effects are temporary
• the ozone layer: reduces the amount of UV radiation from the sun that reaches the Earth's surface.

  • it is found in the stratosphere
  • 3O2 (g) →(reversible reaction) ← 2O3 (g) (ozone molecules break up to reform oxygen when they absorb UV radiation)
• depletion of ozone layer:

  • chloroflurocarbons (CFCs): found in aerosol propellants and refrigerants. They interact with UV radiation to produce chlorine atoms which react with ozone
  • (1) CFCs → (UV) →chlorine atoms (2) chlorine atom + ozone molecules → chlorine oxide + oxygen (3) chlorine oxide + ozone molecules → chlorine atom + oxygen
  • chlorine atoms present at the start of the reaction is regenerated at the end of the 2nd reaction. thus, more O3 molecules are reacted with. (1 Cl atom can destroy many O3 molecules)
  • this can cause skin cancer rates to increase
• the carbon cycle describes a set of processes that regulates the amount of CO2 in the atmosphere

  • the balance between processes that produces CO2 (combustion and respiration) and the processes that removes CO2 (photosynthesis) regulates the amount of CO2 in the atmosphere
• global warming is the increase in the average temperature of the earth's surface due to increasing amounts of greenhouse gases in the atmosphere
• causes of the greenhouse effect:

  • some solar radiations reaches the atmosphere and passes through it (heat)
  • combustion of fossil fuels (releases greenhouse gases) → CO2 & CH4
  • deforestation
• (climate change and other consequences)

  1. change in rainfall patterns: leads to desertification of fertile land thus decreasing the amount of food produced globally
• (climate change and other consequences)

  2. frequent and severe heat wave : leads to high temperatures and possible heat injuries, destructive wildfire (could destroy ecosystems)
• (climate change and other consequences)

  3. tropical storms ( increase in frequency and intensity of extreme weathers): leading to property damage, lives lost, can permanently decrease the fertility of farmland near the coast due to saltwater deposition
• (climate change and other consequences)

  4. ocean warming and acidification:

  • coral reefs bleached, habitats lost
  • fish population depletion
  • acidified water dissolve the shells of crustaceans
• (climate change and other consequences)

  5. glacial retreat and melting of polar ice caps:

  • glacier-fed river levels would change
  • sea levels would rise, and permanently flood coastal areas
  • climate - stabilising oceans currents would be disrupted
• fossil fuels are from decayed plants and animals millions of years ago. they are mainly organic compounds containing hydrocarbons (carbon and hydrogen)
• combustion is an exothermic process where the thermal energy generated can be converted to other forms of energy
• (fossil fuels)

  1. natural gas: mainly methane

  • colourless and odourless
  • CH4 (g) + 2O2 (g) --> CO2 (g) + 2H2O (g)
  • cleanest form of fossil fuel
  • liquefied before being transported to consumers (it is safer) (gas - liquid reduce volume by 600 times)
  • an additive like tetrahydrothiophene (THT) has a pungent smell and added to natural gas to alert us in cases of a gas leak
• (fossil fuels)

  2. crude oil: petroleum

  • contain mixture of hydrocarbons
  • from drilling of underground reservoirs
  • different hydrocarbons in crude oil burns at different temperatures and are miscible
  • it is separated into useful fractions by fractional distillation
• (fossil fuels)

  natural gas and crude oil are considered non- renewable sources of energy. there are limited amounts of these sources and they cannot be replaced quickly enough to keep up with our rate of use.
• crude oil have hydrocarbons with 1 - 70 carbon atoms per molecules

  • more carbon atoms in each molecule: higher boiling point, more viscous (thick and sticky consistency)
  • less carbon atoms in each molecule: lower boiling points, less viscous and burns more easily
• (separation of crude oil)

  1. crude oil heated in furnace to 400°c
  2. vapour passed into fractionating column
  3. fraction with highest boiling point is collected last and condenses at high temps --> collected at bottom of column
  4. fractions with lowest boiling points condenses at lower temperatures thus, they rise up before they condense and are collected at the top
• (crude oil fractions)

  • petroleum (70°c)
  • naphthalene (120°c)
  • kerosene (170°c)
  • diesel (270°c)
  • lubricating oil
  • fuel oil
  • bitumen

  90% used as fuels: generate thermal energy and electricity to power household appliances, motor vehicles and industrial activities

  10% used as petrochemical feedstock: manufacture of plastic, detergent, medicine, fertilisers, pesticides, synthetic rubber (daily products)
• conversing crude oil --> due to limited supply

  1. take public transport, drive smaller cars consuming less fuel
  2. use solar energy, biofuels, nuclear energy (uranium) --> risk of harmful radiation from nuclear plants
  3. electric vehicles
• biofuels are alternative renewable energy source to crude oil and natural gas

  • ethanol obtained fermentation of sugar in sugarcane plants or corn --> regrown quickly (making it a renewable energy source)
• (sugarcane to bioethanol)

  sugarcane --(crushed)

  --> sugarcane bagasse --> alkali/acid treatment --> fermentation --> fractional distillation--> bioethanol & waste products
• • bioethanol is more environmentally sustainable as sugarcane absorbed CO2 when it grows during photosynthesis thus, offsetting the CO2 production when it is burnt
  • (chemical eqn): C2H5OH (l) + 3O2 (g) --> 2CO2 (g) + 3H2O (g)
  • many sugarcane plants needs to be planted (requires fertilisers from crude oil fractions)
  • the transportation of it for treatment requires burning of fossil fuels ---> more CO2 produced
  • amount of CO2 produced should be considered to produce biofuels at a low cost with less impact on the environment