According to Le Chatelier's Principle, how does changing temperature or pressure shift the equilibrium: N2(g) + 3H2(g) ⇌ 2NH3(g) (ΔH = -92 kJ/mol)?

The forward reaction is exothermic and reduces gas moles from 4 moles to 2 moles. Decreasing temperature shifts equilibrium to the right (exothermic direction) to increase ammonia yield. Increasing pressure shifts equilibrium to the right (side with fewer moles of gas) to increase ammonia yield.

State the four standard GCSE laboratory tests for Hydrogen, Oxygen, Carbon Dioxide, and Chlorine gases.

Hydrogen (H2): lighted splint gives a 'squeaky pop'. Oxygen (O2): relights a glowing splint. Carbon dioxide (CO2): bubbling through limewater (aqueous calcium hydroxide, Ca(OH)2) turns it cloudy/milky (forming insoluble CaCO3 precipitate). Chlorine (Cl2): bleaches damp blue litmus paper red then white.

What are the main stages of sewage and wastewater treatment?

1) Screening and grit removal (removes large debris/plastics); 2) Sedimentation in settlement tanks separates sewage into heavy organic sludge (at the bottom) and liquid effluent (on top); 3) Aerobic biological treatment of effluent by aerobic bacteria; 4) Anaerobic digestion of solid sludge by bacteria (producing methane biogas and fertiliser).

Use Collision Theory to explain why increasing concentration (or gas pressure) or surface area of a solid increases reaction rate.

Increasing concentration/pressure packs more particles into a given volume (and crushing a solid into a powder exposes more surface particles). This increases the frequency of collisions (more collisions per unit time), which increases the rate of reaction.

What are the four stages evaluated in a Life Cycle Assessment (LCA) of a product?

1) Extracting and processing raw materials; 2) Manufacturing and packaging; 3) Use and operation during the product's lifetime; 4) Disposal at the end of its useful life (landfill, incineration, or recycling), including transport and energy consumption at every stage.

What are the sources and environmental/health effects of SO2, NOx, CO, and particulates from burning fuels?

Sulfur dioxide (SO2, from sulfur impurities in coal/oil) and Nitrogen oxides (NOx, from N2 + O2 reacting in hot car engines) dissolve in rainwater to cause acid rain and respiratory problems. Carbon monoxide (CO, incomplete combustion) is a toxic gas. Particulates (soot/unburnt hydrocarbons) cause global dimming and lung disease.

What are the naturally occurring polymers formed from glucose, amino acids, and nucleotides?

Glucose monomers polymerise to form starch and cellulose (polysaccharides). Amino acid monomers (containing -NH2 amine and -COOH carboxylic acid groups) polymerise via peptide links to form polypeptides/proteins. Nucleotide monomers polymerise to form DNA (two polymer chains in a double helix).

In paper chromatography, what are the mobile and stationary phases, and how do you calculate the Rf value?

Stationary phase: the chromatography paper (cellulose fibres/trapped water). Mobile phase: the solvent (water or ethanol) that moves up the paper. Rf = Distance moved by substance spot (from pencil baseline) ÷ Distance moved by solvent front (always < 1, no units).

What are the flame test colours for Lithium (Li⁺), Sodium (Na⁺), Potassium (K⁺), Calcium (Ca²⁺), and Copper (Cu²⁺) ions (Triple Science)?

Lithium (Li⁺): Crimson red. Sodium (Na⁺): Yellow. Potassium (K⁺): Lilac. Calcium (Ca²⁺): Orange-red (brick red). Copper (Cu²⁺): Green (blue-green).

How do you distinguish between a pure substance and an impure mixture using melting/boiling points, and what is a formulation?

In chemistry, a pure substance is a single element or compound that melts and boils at a sharp, specific temperature, whereas an impure mixture melts/boils over a range of temperatures (lower melting point, higher boiling point). A formulation is a mixture designed in exact measured proportions so that each component contributes a specific property (e.g., paints, fuels, medicines, alloys).

Describe the two methods for the GCSE Rates of Reaction Required Practical (Sodium thiosulfate + HCl and Magnesium + HCl).

1) Disappearing cross (turbidity): react sodium thiosulfate with HCl in a conical flask over a black cross and time how long it takes for the yellow sulfur precipitate to obscure the cross at different concentrations. 2) Gas collection: react Mg ribbon with HCl and measure the volume of H2 gas collected in a gas syringe (or inverted measuring cylinder) every 10 seconds.

Contrast thermosoftening polymers and thermosetting polymers in terms of intermolecular cross-links and behaviour when heated (Triple Science).

Thermosoftening polymers consist of tangled polymer chains with weak intermolecular forces and NO covalent cross-links between chains, so they soften and melt when heated and can be remoulded. Thermosetting polymers have strong covalent cross-links between polymer chains, so they do not melt when heated and retain their rigid shape.

How does a catalyst increase the rate of a chemical reaction without being used up?

A catalyst provides an alternative reaction pathway with a lower activation energy (Ea). Therefore, a greater proportion of colliding particles have sufficient energy (E ≥ Ea) to react successfully upon collision.

Compare the two industrial methods of manufacturing ethanol: fermentation of glucose vs hydration of ethene.

Fermentation: Glucose → Ethanol + CO2 using yeast enzymes at ~30°C in anaerobic conditions (renewable sugar cane feedstock, batch process, produces dilute aqueous ethanol requiring fractional distillation). Hydration of ethene: Ethene + Steam → Ethanol (non-renewable crude oil feedstock, continuous fast process, 100% atom economy, pure product).

Use Collision Theory to explain why increasing temperature dramatically increases the rate of a chemical reaction.

1) Particles gain kinetic energy and move faster, colliding more frequently (more collisions per second); 2) A much higher proportion of colliding particles have energy greater than or equal to the activation energy (E ≥ Ea), resulting in a higher frequency of successful collisions.

What is cracking of long-chain hydrocarbons, what are the two industrial methods, and why is cracking economically essential?

Cracking is the thermal decomposition of long-chain saturated alkanes into shorter-chain alkanes (high-demand fuels like petrol) and unsaturated alkenes (starting materials for polymers/plastics). Catalytic cracking: ~550°C with a zeolite (aluminium oxide/silicon dioxide) catalyst. Steam cracking: ~800°C mixed with steam and no catalyst.

What is the general formula of alkenes, why are they described as unsaturated, and what is the chemical test for an alkene?

Alkenes have general formula CnH2n and contain a C=C double covalent bond (unsaturated because they contain two fewer hydrogen atoms than the corresponding alkane). Test: shake with orange bromine water (Br2(aq)); an alkene decolourises bromine water from orange-brown to colourless via an addition reaction.

Why does iron rust, how do sacrificial protection and galvanising prevent rusting, and what are common alloys (brass, bronze, steels)?

Rusting (hydrated iron(III) oxide) requires BOTH oxygen and water. Galvanising coats iron in zinc, which acts as a physical barrier AND provides sacrificial protection because zinc is more reactive than iron and oxidises (loses electrons) preferentially. Bronze = Cu + Sn; Brass = Cu + Zn; Stainless steel = Fe + Cr + Ni (resists corrosion).

Explain step-by-step how fractional distillation separates crude oil into fractions and how hydrocarbon properties change with chain length.

1) Crude oil is heated and vaporised before entering a fractionating column that is hot at the bottom and cool at the top; 2) Vapours rise and condense at different heights when they reach a tray at or below their boiling point. Longer-chain hydrocarbons have stronger intermolecular forces, meaning higher boiling points, higher viscosity (thicker), and lower flammability.

What are the approximate percentages of gases in Earth's modern atmosphere, and how did it evolve from the early volcanic atmosphere?

Modern atmosphere: ~78% Nitrogen (N2), ~21% Oxygen (O2), ~0.9% Argon, ~0.04% Carbon dioxide (CO2). Early volcanic atmosphere was mostly CO2 and water vapour: water vapour condensed to form oceans; CO2 dissolved in oceans to form carbonate precipitates/sedimentary limestone; photosynthetic algae and plants evolved (~2.7 billion years ago), absorbing CO2 and releasing O2.

State the chemical tests and positive results for Carbonate (CO3²⁻), Sulfate (SO4²⁻), and Halide (Cl⁻, Br⁻, I⁻) anions.

Carbonates: add dilute acid → effervescence of CO2 gas that turns limewater cloudy. Sulfates: add dilute HCl followed by barium chloride solution (BaCl2) → white precipitate of barium sulfate (BaSO4). Halides: add dilute nitric acid (HNO3) followed by silver nitrate solution (AgNO3) → Cl⁻ gives white precipitate (AgCl), Br⁻ gives cream precipitate (AgBr), I⁻ gives yellow precipitate (AgI).

What are the compromise conditions used in the industrial Haber Process (N2 + 3H2 ⇌ 2NH3) and why are they chosen?

Temperature: 450°C (a compromise—low enough to give a reasonable equilibrium yield of NH3 since the forward reaction is exothermic, but high enough for a fast rate of reaction). Pressure: 200 atmospheres (high enough to favour the forward reaction with fewer gas moles, without making containment pipes dangerously expensive). Catalyst: Iron (speeds up rate of attainment of equilibrium without changing yield).

How do alkenes react with hydrogen (H2), steam (H2O), and halogens (Br2/Cl2) in addition reactions (Triple Science)?

The C=C double bond opens up to form a single C-C bond: 1) Hydrogenation (+ H2 with a nickel catalyst at 150°C) produces an alkane; 2) Hydration (+ steam at 300°C, 60–70 atm with a phosphoric acid catalyst) produces an alcohol (e.g., ethene + steam ⇌ ethanol); 3) Halogenation (+ Br2) produces a dihaloalkane (e.g., 1,2-dibromoethane).

What is crude oil, what is the general formula of alkanes, and what are the first four alkanes?

Crude oil is a finite mixture of hydrocarbons (compounds containing hydrogen and carbon atoms only), mostly homologous alkanes with general formula CnH2n+2. The first four alkanes are Methane (CH4), Ethane (C2H6), Propane (C3H8), and Butane (C4H10).

How is fresh water (groundwater/rivers) treated to make potable water, and how is seawater desalinated?

Freshwater treatment: 1) Filtration through wire mesh screens and sand/gravel beds to remove insoluble solids; 2) Sterilisation using chlorine gas, ozone, or UV light to kill harmful microbes. Desalination of salty seawater: Distillation (boiling and condensing) or Reverse Osmosis (forcing water through membranes under high pressure)—both require large amounts of energy.

State the two equations for mean rate of reaction and how to find the instantaneous rate at time t from a curve.

Mean rate = Quantity of reactant used ÷ Time taken, OR Quantity of product formed ÷ Time taken (in g/s, cm³/s, or mol/s). To find the instantaneous rate at a specific time t on a curved graph, draw a tangent to the curve at time t and calculate its gradient (change in y ÷ change in x).

Compare complete and incomplete combustion of hydrocarbons and explain why carbon monoxide (CO) is toxic.

Complete combustion (plentiful O2): Hydrocarbon + Oxygen → Carbon dioxide + Water (releases maximum energy). Incomplete combustion (limited O2): produces Carbon monoxide (CO) and/or soot particulates (C) + Water. CO is a colourless, odourless toxic gas that binds irreversibly to haemoglobin in red blood cells, reducing oxygen transport.

Explain the physical mechanism of the Greenhouse Effect in terms of short-wavelength and long-wavelength radiation.

1) Short-wavelength (ultraviolet and visible) radiation from the Sun passes unabsorbed through the Earth's atmosphere; 2) The Earth's surface absorbs this radiation, warms up, and re-emits it as longer-wavelength infrared (thermal) radiation; 3) Greenhouse gases (CO2, CH4, H2O vapour) absorb and re-radiate this long-wavelength infrared radiation back towards Earth, trapping heat.

What precipitates form when sodium hydroxide solution (NaOH(aq)) is added to solutions containing Cu²⁺, Fe²⁺, Fe³⁺, Al³⁺, Ca²⁺, and Mg²⁺ ions?

Cu²⁺: Blue precipitate of Cu(OH)2. Fe²⁺: Green precipitate of Fe(OH)2. Fe³⁺: Brown (rust-coloured) precipitate of Fe(OH)3. Al³⁺, Ca²⁺, and Mg²⁺ all form white precipitates, but ONLY the Al(OH)3 precipitate redissolves in excess NaOH solution to form a colourless solution.

What is dynamic equilibrium in a reversible reaction in a closed system?

Dynamic equilibrium is reached in a closed system (where no reactants or products can escape) when the rate of the forward reaction equals the rate of the reverse reaction, so the concentrations of reactants and products remain constant.

Compare addition polymerisation and condensation polymerisation (Triple Science).

Addition polymerisation: unsaturated alkene monomers (with C=C bonds) join together to form a long saturated polymer chain as the only product (100% atom economy, e.g., ethene → poly(ethene)). Condensation polymerisation: monomers with two functional groups (e.g., a diol + a dicarboxylic acid) react to form a polyester and eliminate a small molecule such as water (H2O).

How do phytomining and bioleaching extract copper from low-grade copper ores?

Phytomining: plants are grown on low-grade ore soil, absorb copper ions through their roots, and are harvested and burned to produce ash rich in copper compounds. Bioleaching: bacteria feed on low-grade ores to produce an acidic leachate solution containing copper ions. In both methods, pure copper is extracted from the solution by displacement with scrap iron or by electrolysis.

GCSE Chemistry Paper 2: Rates of Reaction, Equilibrium, Organic Chemistry, Chemical Analysis & Atmosphere

High-yield GCSE/IGCSE Chemistry Paper 2: collision theory, Le Chatelier's principle, Haber process compromises, fractional distillation of crude oil, alkanes/alkenes/polymers, gas/flame/ion tests, greenhouse effect, and potable water treatment.

Level: intermediate
Languages: en → en
Cards: 32
Markdown: GCSE Chemistry Paper 2: Rates of Reaction, Equilibrium, Organic Chemistry, Chemical Analysis & Atmosphere (.md)

Flashcards (32)

#	Front (Term / Question)	Back (Definition / Answer)
1	According to Le Chatelier's Principle, how does changing temperature or pressure shift the equilibrium: N2(g) + 3H2(g) ⇌ 2NH3(g) (ΔH = -92 kJ/mol)?	The forward reaction is exothermic and reduces gas moles from 4 moles to 2 moles. Decreasing temperature shifts equilibrium to the right (exothermic direction) to increase ammonia yield. Increasing pressure shifts equilibrium to the right (side with fewer moles of gas) to increase ammonia yield.
2	State the four standard GCSE laboratory tests for Hydrogen, Oxygen, Carbon Dioxide, and Chlorine gases.	Hydrogen (H2): lighted splint gives a 'squeaky pop'. Oxygen (O2): relights a glowing splint. Carbon dioxide (CO2): bubbling through limewater (aqueous calcium hydroxide, Ca(OH)2) turns it cloudy/milky (forming insoluble CaCO3 precipitate). Chlorine (Cl2): bleaches damp blue litmus paper red then white.
3	What are the main stages of sewage and wastewater treatment?	1) Screening and grit removal (removes large debris/plastics); 2) Sedimentation in settlement tanks separates sewage into heavy organic sludge (at the bottom) and liquid effluent (on top); 3) Aerobic biological treatment of effluent by aerobic bacteria; 4) Anaerobic digestion of solid sludge by bacteria (producing methane biogas and fertiliser).
4	Use Collision Theory to explain why increasing concentration (or gas pressure) or surface area of a solid increases reaction rate.	Increasing concentration/pressure packs more particles into a given volume (and crushing a solid into a powder exposes more surface particles). This increases the frequency of collisions (more collisions per unit time), which increases the rate of reaction.
5	What are the four stages evaluated in a Life Cycle Assessment (LCA) of a product?	1) Extracting and processing raw materials; 2) Manufacturing and packaging; 3) Use and operation during the product's lifetime; 4) Disposal at the end of its useful life (landfill, incineration, or recycling), including transport and energy consumption at every stage.
6	What are the sources and environmental/health effects of SO2, NOx, CO, and particulates from burning fuels?	Sulfur dioxide (SO2, from sulfur impurities in coal/oil) and Nitrogen oxides (NOx, from N2 + O2 reacting in hot car engines) dissolve in rainwater to cause acid rain and respiratory problems. Carbon monoxide (CO, incomplete combustion) is a toxic gas. Particulates (soot/unburnt hydrocarbons) cause global dimming and lung disease.
7	What are the naturally occurring polymers formed from glucose, amino acids, and nucleotides?	Glucose monomers polymerise to form starch and cellulose (polysaccharides). Amino acid monomers (containing -NH2 amine and -COOH carboxylic acid groups) polymerise via peptide links to form polypeptides/proteins. Nucleotide monomers polymerise to form DNA (two polymer chains in a double helix).
8	In paper chromatography, what are the mobile and stationary phases, and how do you calculate the Rf value?	Stationary phase: the chromatography paper (cellulose fibres/trapped water). Mobile phase: the solvent (water or ethanol) that moves up the paper. Rf = Distance moved by substance spot (from pencil baseline) ÷ Distance moved by solvent front (always < 1, no units).
9	What are the flame test colours for Lithium (Li⁺), Sodium (Na⁺), Potassium (K⁺), Calcium (Ca²⁺), and Copper (Cu²⁺) ions (Triple Science)?	Lithium (Li⁺): Crimson red. Sodium (Na⁺): Yellow. Potassium (K⁺): Lilac. Calcium (Ca²⁺): Orange-red (brick red). Copper (Cu²⁺): Green (blue-green).
10	How do you distinguish between a pure substance and an impure mixture using melting/boiling points, and what is a formulation?	In chemistry, a pure substance is a single element or compound that melts and boils at a sharp, specific temperature, whereas an impure mixture melts/boils over a range of temperatures (lower melting point, higher boiling point). A formulation is a mixture designed in exact measured proportions so that each component contributes a specific property (e.g., paints, fuels, medicines, alloys).
11	Describe the two methods for the GCSE Rates of Reaction Required Practical (Sodium thiosulfate + HCl and Magnesium + HCl).	1) Disappearing cross (turbidity): react sodium thiosulfate with HCl in a conical flask over a black cross and time how long it takes for the yellow sulfur precipitate to obscure the cross at different concentrations. 2) Gas collection: react Mg ribbon with HCl and measure the volume of H2 gas collected in a gas syringe (or inverted measuring cylinder) every 10 seconds.
12	Contrast thermosoftening polymers and thermosetting polymers in terms of intermolecular cross-links and behaviour when heated (Triple Science).	Thermosoftening polymers consist of tangled polymer chains with weak intermolecular forces and NO covalent cross-links between chains, so they soften and melt when heated and can be remoulded. Thermosetting polymers have strong covalent cross-links between polymer chains, so they do not melt when heated and retain their rigid shape.
13	How does a catalyst increase the rate of a chemical reaction without being used up?	A catalyst provides an alternative reaction pathway with a lower activation energy (Ea). Therefore, a greater proportion of colliding particles have sufficient energy (E ≥ Ea) to react successfully upon collision.
14	Compare the two industrial methods of manufacturing ethanol: fermentation of glucose vs hydration of ethene.	Fermentation: Glucose → Ethanol + CO2 using yeast enzymes at ~30°C in anaerobic conditions (renewable sugar cane feedstock, batch process, produces dilute aqueous ethanol requiring fractional distillation). Hydration of ethene: Ethene + Steam → Ethanol (non-renewable crude oil feedstock, continuous fast process, 100% atom economy, pure product).
15	Use Collision Theory to explain why increasing temperature dramatically increases the rate of a chemical reaction.	1) Particles gain kinetic energy and move faster, colliding more frequently (more collisions per second); 2) A much higher proportion of colliding particles have energy greater than or equal to the activation energy (E ≥ Ea), resulting in a higher frequency of successful collisions.
16	What is cracking of long-chain hydrocarbons, what are the two industrial methods, and why is cracking economically essential?	Cracking is the thermal decomposition of long-chain saturated alkanes into shorter-chain alkanes (high-demand fuels like petrol) and unsaturated alkenes (starting materials for polymers/plastics). Catalytic cracking: ~550°C with a zeolite (aluminium oxide/silicon dioxide) catalyst. Steam cracking: ~800°C mixed with steam and no catalyst.
17	What is the general formula of alkenes, why are they described as unsaturated, and what is the chemical test for an alkene?	Alkenes have general formula CnH2n and contain a C=C double covalent bond (unsaturated because they contain two fewer hydrogen atoms than the corresponding alkane). Test: shake with orange bromine water (Br2(aq)); an alkene decolourises bromine water from orange-brown to colourless via an addition reaction.
18	Why does iron rust, how do sacrificial protection and galvanising prevent rusting, and what are common alloys (brass, bronze, steels)?	Rusting (hydrated iron(III) oxide) requires BOTH oxygen and water. Galvanising coats iron in zinc, which acts as a physical barrier AND provides sacrificial protection because zinc is more reactive than iron and oxidises (loses electrons) preferentially. Bronze = Cu + Sn; Brass = Cu + Zn; Stainless steel = Fe + Cr + Ni (resists corrosion).
19	Explain step-by-step how fractional distillation separates crude oil into fractions and how hydrocarbon properties change with chain length.	1) Crude oil is heated and vaporised before entering a fractionating column that is hot at the bottom and cool at the top; 2) Vapours rise and condense at different heights when they reach a tray at or below their boiling point. Longer-chain hydrocarbons have stronger intermolecular forces, meaning higher boiling points, higher viscosity (thicker), and lower flammability.
20	What are the approximate percentages of gases in Earth's modern atmosphere, and how did it evolve from the early volcanic atmosphere?	Modern atmosphere: ~78% Nitrogen (N2), ~21% Oxygen (O2), ~0.9% Argon, ~0.04% Carbon dioxide (CO2). Early volcanic atmosphere was mostly CO2 and water vapour: water vapour condensed to form oceans; CO2 dissolved in oceans to form carbonate precipitates/sedimentary limestone; photosynthetic algae and plants evolved (~2.7 billion years ago), absorbing CO2 and releasing O2.
21	State the chemical tests and positive results for Carbonate (CO3²⁻), Sulfate (SO4²⁻), and Halide (Cl⁻, Br⁻, I⁻) anions.	Carbonates: add dilute acid → effervescence of CO2 gas that turns limewater cloudy. Sulfates: add dilute HCl followed by barium chloride solution (BaCl2) → white precipitate of barium sulfate (BaSO4). Halides: add dilute nitric acid (HNO3) followed by silver nitrate solution (AgNO3) → Cl⁻ gives white precipitate (AgCl), Br⁻ gives cream precipitate (AgBr), I⁻ gives yellow precipitate (AgI).
22	What are the compromise conditions used in the industrial Haber Process (N2 + 3H2 ⇌ 2NH3) and why are they chosen?	Temperature: 450°C (a compromise—low enough to give a reasonable equilibrium yield of NH3 since the forward reaction is exothermic, but high enough for a fast rate of reaction). Pressure: 200 atmospheres (high enough to favour the forward reaction with fewer gas moles, without making containment pipes dangerously expensive). Catalyst: Iron (speeds up rate of attainment of equilibrium without changing yield).
23	How do alkenes react with hydrogen (H2), steam (H2O), and halogens (Br2/Cl2) in addition reactions (Triple Science)?	The C=C double bond opens up to form a single C-C bond: 1) Hydrogenation (+ H2 with a nickel catalyst at 150°C) produces an alkane; 2) Hydration (+ steam at 300°C, 60–70 atm with a phosphoric acid catalyst) produces an alcohol (e.g., ethene + steam ⇌ ethanol); 3) Halogenation (+ Br2) produces a dihaloalkane (e.g., 1,2-dibromoethane).
24	What is crude oil, what is the general formula of alkanes, and what are the first four alkanes?	Crude oil is a finite mixture of hydrocarbons (compounds containing hydrogen and carbon atoms only), mostly homologous alkanes with general formula CnH2n+2. The first four alkanes are Methane (CH4), Ethane (C2H6), Propane (C3H8), and Butane (C4H10).
25	How is fresh water (groundwater/rivers) treated to make potable water, and how is seawater desalinated?	Freshwater treatment: 1) Filtration through wire mesh screens and sand/gravel beds to remove insoluble solids; 2) Sterilisation using chlorine gas, ozone, or UV light to kill harmful microbes. Desalination of salty seawater: Distillation (boiling and condensing) or Reverse Osmosis (forcing water through membranes under high pressure)—both require large amounts of energy.
26	State the two equations for mean rate of reaction and how to find the instantaneous rate at time t from a curve.	Mean rate = Quantity of reactant used ÷ Time taken, OR Quantity of product formed ÷ Time taken (in g/s, cm³/s, or mol/s). To find the instantaneous rate at a specific time t on a curved graph, draw a tangent to the curve at time t and calculate its gradient (change in y ÷ change in x).
27	Compare complete and incomplete combustion of hydrocarbons and explain why carbon monoxide (CO) is toxic.	Complete combustion (plentiful O2): Hydrocarbon + Oxygen → Carbon dioxide + Water (releases maximum energy). Incomplete combustion (limited O2): produces Carbon monoxide (CO) and/or soot particulates (C) + Water. CO is a colourless, odourless toxic gas that binds irreversibly to haemoglobin in red blood cells, reducing oxygen transport.
28	Explain the physical mechanism of the Greenhouse Effect in terms of short-wavelength and long-wavelength radiation.	1) Short-wavelength (ultraviolet and visible) radiation from the Sun passes unabsorbed through the Earth's atmosphere; 2) The Earth's surface absorbs this radiation, warms up, and re-emits it as longer-wavelength infrared (thermal) radiation; 3) Greenhouse gases (CO2, CH4, H2O vapour) absorb and re-radiate this long-wavelength infrared radiation back towards Earth, trapping heat.
29	What precipitates form when sodium hydroxide solution (NaOH(aq)) is added to solutions containing Cu²⁺, Fe²⁺, Fe³⁺, Al³⁺, Ca²⁺, and Mg²⁺ ions?	Cu²⁺: Blue precipitate of Cu(OH)2. Fe²⁺: Green precipitate of Fe(OH)2. Fe³⁺: Brown (rust-coloured) precipitate of Fe(OH)3. Al³⁺, Ca²⁺, and Mg²⁺ all form white precipitates, but ONLY the Al(OH)3 precipitate redissolves in excess NaOH solution to form a colourless solution.
30	What is dynamic equilibrium in a reversible reaction in a closed system?	Dynamic equilibrium is reached in a closed system (where no reactants or products can escape) when the rate of the forward reaction equals the rate of the reverse reaction, so the concentrations of reactants and products remain constant.
31	Compare addition polymerisation and condensation polymerisation (Triple Science).	Addition polymerisation: unsaturated alkene monomers (with C=C bonds) join together to form a long saturated polymer chain as the only product (100% atom economy, e.g., ethene → poly(ethene)). Condensation polymerisation: monomers with two functional groups (e.g., a diol + a dicarboxylic acid) react to form a polyester and eliminate a small molecule such as water (H2O).
32	How do phytomining and bioleaching extract copper from low-grade copper ores?	Phytomining: plants are grown on low-grade ore soil, absorb copper ions through their roots, and are harvested and burned to produce ash rich in copper compounds. Bioleaching: bacteria feed on low-grade ores to produce an acidic leachate solution containing copper ions. In both methods, pure copper is extracted from the solution by displacement with scrap iron or by electrolysis.