National Year 11 Chemistry
Chapters: 5
1. 4.6 The rate and extent of chemical change
4.6.1 Rate of reaction · 4.6.2 Reversible reactions and dynamic equilibrium
- Rates of Reaction – The rate of a reaction is how fast reactants are used up or products are made. Rate = change in amount ÷ time. Particles must collide with at least the activation energy to react. More frequent, more energetic collisions mean a faster rate. Raising concentration (or gas pressure), temperature or surface area, or adding a catalyst, makes reactions faster. A catalyst gives a path with lower activation energy and is not used up.
- Chemical Equilibrium: Kc, Kp, Q and Gibbs Energy – In a closed container a reversible reaction goes both ways. After some time the forward and backward rates become equal, so amounts stop changing, but the reaction does not stop. This is dynamic equilibrium. At equilibrium the ratio of products to reactants (each raised to its coefficient) is a fixed number, the equilibrium constant K. Kc uses concentrations, Kp uses partial pressures, and Kp = Kc(RT)^Δn. Pure solids and liquids are left out of K. The reaction quotient Q tells the direction: Q < K goes forward, Q > K goes backward, Q = K is equilibrium. K and Gibbs energy are linked: ΔG = ΔG° + RT ln Q and ΔG° = −RT ln K.
2. 4.7 Organic chemistry
4.7.1 Carbon compounds as fuels and feedstock · 4.7.2 Reactions of alkenes and alcohols (Chemistry only) · 4.7.3 Synthetic and naturally occurring polymers (Chemistry only)
- Carbon and Its Compounds: Bonding, Hydrocarbons and Naming – Carbon has 4 outer electrons, so it shares electrons (covalent bonds) instead of gaining or losing them. Because it bonds to itself (catenation) and always makes 4 bonds (tetravalency), it forms millions of compounds: chains, branches and rings, saturated or unsaturated. Compounds with the same functional group form a homologous series that differs by –CH₂–, and IUPAC names are built from the number of carbons + a suffix or prefix for the functional group.
- Chemical Properties of Carbon Compounds, Ethanol and Ethanoic Acid – Carbon compounds burn in oxygen to give CO₂, water, heat and light (combustion); strong oxidising agents turn alcohols into acids (oxidation); unsaturated compounds add hydrogen with a nickel catalyst (addition); saturated compounds swap hydrogen for chlorine in sunlight (substitution). Ethanol reacts with sodium to give hydrogen and dehydrates to ethene; ethanoic acid is a weak acid that makes esters with alcohols and CO₂ with carbonates.
- Polymers – A polymer is a giant molecule made by joining many small molecules (monomers) into a long chain. In addition polymerisation, monomers with a C=C double bond open up and link with nothing lost (ethene → poly(ethene)). In condensation polymerisation, two kinds of monomer with reactive groups at both ends join and give off a small molecule such as water at every link (nylon, polyester). Nature makes polymers too: starch, cellulose, proteins, DNA, rubber. Separate chains give thermoplastics that melt and can be recycled; cross-linked chains give thermosets that never melt. Most plastics do not rot, so we must reduce, reuse and recycle them.
3. 4.8 Chemical analysis
4.8.1 Purity, formulations and chromatography · 4.8.2 Identification of common gases · 4.8.3 Identification of ions by chemical and spectroscopic means (Chemistry only)
- Mixtures and Their Separation – A mixture has two or more substances mixed without any fixed ratio, and each keeps its own properties. Homogeneous mixtures (solutions) look the same everywhere; heterogeneous ones do not. By particle size we get solutions (< 1 nm), colloids (1–1000 nm) and suspensions (> 1000 nm). Colloids scatter light (Tyndall effect). Concentration tells how much solute is in a solution. We separate mixtures by using a difference in their parts: evaporation, crystallisation, distillation, chromatography, sublimation, centrifugation and coagulation.
- Tests for Gases: How to Identify Hydrogen, Oxygen, Carbon Dioxide, Chlorine and Ammonia – Most gases have no colour, so we identify them with a simple test that gives a clear sign. Hydrogen: a lit splint gives a squeaky pop. Oxygen: a glowing splint relights. Carbon dioxide: limewater turns milky. Chlorine: damp blue litmus turns red, then white (bleached). Ammonia: damp red litmus turns blue. Water vapour turns white anhydrous copper(II) sulfate blue. Sulfur dioxide turns acidified potassium manganate(VII) from purple to colourless.
- Tests for Ions: Flame Tests, Hydroxide Precipitates, Anion Tests and Flame Emission Spectroscopy – An ionic compound is made of a positive metal ion and a negative ion. Each can be found with its own test. Flame tests show metal ions by colour: lithium crimson, sodium yellow, potassium lilac, calcium orange-red, copper green. Sodium hydroxide gives coloured hydroxide precipitates: Cu²⁺ blue, Fe²⁺ green, Fe³⁺ brown, Al³⁺, Ca²⁺ and Mg²⁺ white (only Al(OH)₃ dissolves in excess). Carbonates fizz with acid and the gas turns limewater milky. Halides with acidified silver nitrate: chloride white, bromide cream, iodide yellow. Sulfates with acidified barium chloride: white precipitate. Instruments such as flame emission spectroscopy are faster, more sensitive and can measure amounts.
4. 4.9 Chemistry of the atmosphere
4.9.1 The composition and evolution of the Earth's atmosphere · 4.9.2 Carbon dioxide and methane as greenhouse gases · 4.9.3 Common atmospheric pollutants and their sources
- The Composition and Evolution of Earth's Atmosphere – Today dry air is about 78% nitrogen, 21% oxygen and about 1% argon, with tiny amounts of carbon dioxide (about 0.04%) and other gases. Earth's early atmosphere came from volcanoes: mostly carbon dioxide and water vapour, with little or no oxygen. As Earth cooled, water vapour condensed into oceans and some CO2 dissolved. Algae and later plants made oxygen by photosynthesis. Carbon was locked away in sedimentary rocks such as limestone and in fossil fuels, so CO2 fell.
- Climate Change and the Greenhouse Effect – Climate is the average weather of a place over about 30 years. Greenhouse gases like carbon dioxide and methane trap some of the heat the Earth gives off. Humans have added a lot more of these gases by burning fossil fuels and cutting forests, so the Earth is warming. This causes melting ice, rising seas and more extreme weather. We can cut emissions (mitigation) and prepare for changes (adaptation).
- Pollution: Air, Water, Land and Noise – Pollution is the release of harmful substances or energy into air, water or land faster than nature can remove them. Main air pollutants are particulates, carbon monoxide, sulfur dioxide, nitrogen oxides and ozone; they cause acid rain and smog. Water pollution by nutrients, sewage and toxins causes eutrophication and biomagnification. We reduce pollution by cutting emissions at the source, cleaning waste before release, and the 3Rs.
5. 4.10 Using resources
4.10.1 Using the Earth's resources and obtaining potable water · 4.10.2 Life cycle assessment and recycling · 4.10.3 Using materials (Chemistry only) · 4.10.4 The Haber process and the use of NPK fertilisers (Chemistry only)
- Water Purification: From Dirty Water to Safe Drinking Water – Potable water is water that is safe to drink. It is not pure: it still has some dissolved salts, but only small amounts and no harmful germs. To make it, we choose a good source, let solids settle, filter it, and kill germs with chlorine, ozone or UV light. Where fresh water is short, sea water is desalinated by distillation or reverse osmosis. Waste water from homes and farms is treated before it goes back to rivers. Hard water has dissolved calcium and magnesium salts; it can be softened by boiling or ion exchange.
- Life Cycle Assessment and Recycling – A life cycle assessment (LCA) adds up the environmental impact of a product over its whole life: getting the raw materials, making it, using it and getting rid of it. LCAs let us compare products fairly. Reusing and recycling materials such as metals, glass and plastics cut the use of raw materials, energy and landfill.
- Corrosion, Its Prevention and Alloys – Corrosion is the slow eating away of a metal by air, moisture or chemicals around it. Iron rusts only when both air (oxygen) and water are present, forming hydrated iron oxide. It can be prevented by painting, oiling, galvanising, chrome plating, anodising or making alloys. An alloy is a uniform mixture of a metal with other metals or a non-metal; alloys are usually harder, stronger and more corrosion-resistant than the pure metal.
- The Haber Process and NPK Fertilisers – The Haber process makes ammonia from nitrogen (from air) and hydrogen (usually from natural gas): N₂ + 3H₂ ⇌ 2NH₃. The forward reaction is exothermic and reversible. A compromise of about 200 atm, about 450 °C and an iron catalyst gives a reasonable yield at a fast rate. Ammonia is cooled to a liquid and removed; unreacted gases are recycled. Ammonia is used to make nitrogen fertilisers such as ammonium nitrate. NPK fertilisers supply nitrogen, phosphorus and potassium to help crops grow.