Summary
Highlights
The rate of reaction measures how quickly reactants are consumed or products are formed. It can be calculated as the quantity of reactant used or product made divided by time. Units vary, but common ones include grams/second, cm³/second, or moles/second. Graphs illustrating amount of substance versus time show a steep curve for a high reaction rate and a shallow curve for a low rate. Experimental methods include measuring mass change using a balance and stopwatch (for gas production) or volume of gas produced using a gas syringe or inverted measuring cylinder. Mean rate of reaction between two points on a graph is calculated by (change in amount) / (change in time). The instantaneous rate at a specific point is found by drawing a tangent to the curve at that point and calculating its gradient (change in Y / change in X).
Five main factors influence reaction rate: temperature, pressure, concentration, surface area, and catalysts. All are explained using collision theory, which states that reactions occur only when particles collide with sufficient energy (activation energy). Increasing temperature increases particle energy, leading to more frequent and successful collisions. Increasing pressure (for gases) or concentration (for solutions) means particles are more crowded, increasing collision frequency. Increasing surface area exposes more reactant particles, also increasing collision frequency. Catalysts speed up reactions by providing an alternative reaction pathway with a lower activation energy, leading to more successful collisions, without being used up themselves. Catalysts do not affect the position of equilibrium.
Reversible reactions can proceed in both forward and backward directions. If a reaction is endothermic in one direction, it's exothermic in the reverse, with equal energy transfer. Equilibrium occurs when the forward and backward reactions happen at the same rate in a closed system. Le Chatelier's principle explains how changing conditions affect the position of equilibrium: the system adjusts to counteract the change. Increasing reactant concentration shifts equilibrium to the product side, and vice-versa. Increasing temperature shifts equilibrium in the endothermic direction, while decreasing temperature shifts it in the exothermic direction. Increasing pressure shifts equilibrium to the side with fewer gas moles, and vice versa. An example used is the Haber process for ammonia synthesis, which is an exothermic reaction with fewer moles of product gas.
Crude oil is a finite resource, a mixture of hydrocarbons. A hydrocarbon consists only of carbon and hydrogen. Alkanes and alkenes are homologous series. Homologous series share a general formula, successive compounds differ by CH₂, have similar chemical properties, and gradual changes in physical properties. Alkanes have the general formula CnH2n+2, and the first four are methane, ethane, propane, and butane (ending in -ane). Alkenes have a carbon-carbon double bond, general formula CnH2n, and are unsaturated. The first four are ethene, propene, butene, and pentene (ending in -ene). Alkenes are more reactive than alkanes; they decolorize bromine water (orange to colorless), a key test. Alkenes undergo addition reactions (with hydrogen, water, halogens) where the double bond breaks to form single bonds with added atoms.
Crude oil is separated into fractions by fractional distillation. Crude oil is heated in a furnace, vaporized, and enters a fractionating column. The column is hotter at the bottom and cooler at the top. Vapors rise, cool, and condense at different temperatures according to their boiling points; lower boiling point fractions collect higher up. Properties of hydrocarbons change with size: as molecules get larger, boiling points and viscosity increase, but flammability decreases. Cracking is used to break down long, less useful hydrocarbons into smaller, more valuable alkanes (for fuel) and alkenes (for polymers/chemicals). Methods include catalytic cracking (vapors over hot catalyst) and steam cracking (hydrocarbons with steam at high temperatures).
Alcohols contain the -OH functional group. The first four are methanol, ethanol, propanol, and butanol (ending in -anol). Uses include chemical feedstock, fuel, and solvents. Alcohols undergo complete combustion (alcohol + oxygen → CO₂ + H₂O) and react with sodium to produce hydrogen gas. They can also be oxidized by an oxidizing agent (e.g., potassium dichromate) to form carboxylic acids and water. Shorter alcohols are more soluble in water. Ethanol can be made by fermentation of glucose using yeast under anaerobic conditions at 25-35°C. Carboxylic acids contain the -COOH functional group. The first four are methanoic, ethanoic, propanoic, and butanoic acid (ending in -oic acid). They are weak acids (partially ionize in water) and react like other acids with metals, bases, and carbonates. They also react with alcohols to form esters and water (esterification). Esters, like ethyl ethanoate (from ethanol and ethanoic acid), are used as solvents, flavorings, and perfumes, characterized by a fruity smell.
Alkenes form addition polymers, where many small monomer molecules (e.g., ethene) join to form a large polymer (e.g., polyethene) without losing any atoms. The double bond in the monomer opens up to form a single bond in the polymer repeat unit. Condensation polymers are formed from monomers with two different functional groups (e.g., diols and dicarboxylic acids), losing a small molecule like water during polymerization. This forms new bonds, such as ester bonds in polyesters. Polypeptides (proteins) are condensation polymers formed from amino acids (which have both amine and carboxylic acid functional groups). DNA is a large biological polymer made of nucleotide monomers arranged in a double helix, carrying genetic instructions. Starch and cellulose are biological polymers made from sugar monomers, storing energy and providing structure in plants, respectively.
A pure substance is a single element or compound not mixed with others; it has a sharp, defined melting point. Impure substances melt over a range of temperatures. A formulation is a mixture designed for a specific purpose (e.g., fuels, paints, medicines), with components in carefully measured quantities. Chromatography separates mixtures and identifies substances by their movement through a stationary phase (e.g., paper) by a mobile phase (solvent). RF value = (distance moved by substance) / (distance moved by solvent). Pure compounds yield a single spot. Specific tests for gases include: hydrogen (lit splint, squeaky pop), oxygen (glowing splint, relights), carbon dioxide (bubble through limewater, turns milky/cloudy), and chlorine (damp blue litmus paper, bleaches white).
Flame tests identify metal ions in solids: lithium (crimson), sodium (yellow), potassium (lilac), calcium (orange-red), copper (green). Mixtures can mask colors. For metal ions in solution, the sodium hydroxide test uses the color of the precipitate formed: aluminium (white, redissolves in excess NaOH), calcium (white), magnesium (white), copper(II) (blue), iron(II) (green), iron(III) (brown). Carbonate ions are detected by adding dilute acid, producing CO₂ (test with limewater). Halide ions (Cl⁻, Br⁻, I⁻) are tested by adding nitric acid, then silver nitrate. Chloride gives a white precipitate (AgCl), bromide a cream (AgBr), and iodide a yellow (AgI). Sulfate ions are tested by adding barium chloride solution and dilute hydrochloric acid, forming a white precipitate (BaSO₄). Instrumental methods like flame emission spectroscopy are more accurate, sensitive, and rapid than chemical tests. They identify metal ions and their concentrations by analyzing the light emitted when a sample is burned in a flame.
The Earth's atmosphere has been stable for 200 million years (80% nitrogen, 20% oxygen, small amounts of other gases). The early atmosphere (first billion years) was formed from volcanic activity, mainly CO₂, with little to no O₂, and some methane and ammonia. Water vapor condensed to form oceans, where CO₂ dissolved, reducing atmospheric CO₂. Plants and algae evolved, producing O₂ via photosynthesis, leading to increased O₂ levels and further CO₂ reduction. Formation of sedimentary rocks and fossil fuels also reduced atmospheric CO₂. Greenhouse gases (CO₂, methane, water vapor) trap infrared radiation, warming the Earth. Human activities (burning fossil fuels, deforestation, cattle farming, rice farming) increase these gases. Evidence suggests human activity is causing climate change, though factors like model oversimplification, bias, and measurement uncertainties exist. Global warming refers to recent human-induced climate warming, correlated with CO₂ concentration. Effects include melting glaciers, droughts, rising sea levels, and habitat loss. A carbon footprint measures total greenhouse gas emissions.
Combustion of fuels (containing carbon, hydrogen, sulfur) releases pollutants like CO₂, water vapor, carbon monoxide, sulfur dioxide, and nitrogen oxides. Complete combustion (excess oxygen) of hydrocarbons produces CO₂ and água. Incomplete combustion (limited oxygen) produces carbon monoxide (toxic, colorless, odorless) and/or soot (particulate carbon, worsens asthma, causes global dimming). Sulfur impurities in fuels lead to sulfur dioxide (SO₂), which further oxidizes to sulfur trioxide (SO₃). SO₃ dissolves in rainwater to form acid rain (sulfuric acid), harming aquatic life and corroding buildings/statues made of limestone. Car engines' high temperatures and pressures cause nitrogen and oxygen from the air to react, forming nitrogen oxides (NOx), which cause photochemical smog and respiratory problems like asthma.
Humans rely on Earth's resources for food, shelter, transport, warmth, and materials. Finite resources (e.g., fossil fuels) will eventually run out. Sustainable development meets current needs without compromising future generations' ability to meet their own. Obtaining raw materials (metals, glass, ceramics, plastics) by mining and quarrying is energy-intensive and environmentally damaging. Recycling and reusing materials (e.g., glass, metals) reduces resource depletion and environmental impact. Glass can be crushed and melted, or reused. Metals are melted and reformed. Corrosion is the gradual weakening of a metal due to oxidation, like rusting (iron/steel reacting with oxygen and water to form hydrated iron (III) oxide). Rusting can be prevented by barrier methods (painting, oil, plastic, electroplating) or sacrificial protection (contact with a more reactive metal like zinc, which corrodes instead). Aluminium forms a protective oxide layer.
Most metals in everyday use are alloys, mixtures designed for specific properties. Examples include brass (copper + zinc, corrosion-resistant, malleable), bronze (copper + tin, corrosion-resistant), and gold alloys (gold + silver/copper/zinc, stronger than pure gold, shiny). Steel is an iron alloy with carbon and other elements. High carbon steel (1-2% carbon) is strong and brittle (cutting tools). Low carbon steel (<1% carbon) is easy to shape and soft (car bodies). Stainless steel (iron + chromium + nickel) is hard and corrosion-resistant (cutlery). Aluminium alloys are typically low density (aircraft parts). Ceramics include clay ceramics (bricks, pottery - shaped wet clay heated in a furnace, brittle, hard, corrosion-resistant) and glass ceramics. Soda-lime glass (sand, sodium carbonate, limestone) is used for everyday items. Borosilicate glass (sand + boron trioxide) has a higher melting point and is used for labware and ovenware.
Low-density polyethene (LDPE) is made by addition polymerization of ethene under high pressure with oxygen, forming branched polymer chains that don't pack closely, resulting in flexibility and unreactivity (plastic bags). High-density polyethene (HDPE) is made under lower temperature (50°C) with a catalyst, forming straight chains that pack closely, making it strong, flexible, and shatter-resistant (pipes, bottles). Thermosoftening polymers have no cross-links between chains and melt when heated. Thermosetting polymers have strong covalent cross-links, preventing them from melting when heated. Composites consist of a main material (matrix) and reinforcing fibers/fragments (e.g., plywood, concrete).
The Haber process synthesizes ammonia (N₂ + 3H₂ ⇌ 2NH₃) using nitrogen from the air and hydrogen from natural gas. Industrial conditions are 450°C and 200 atmospheres pressure, with an iron catalyst. Ammonia is cooled and condensed, then removed, and unreacted gases are recycled. These conditions are a compromise: low temperatures favor high ammonia yield (exothermic reaction) but slow the rate; high pressures favor high yield (fewer moles product) and increase rate, but are dangerous and costly. The catalyst increases reaction rate without affecting yield. Fertilizers like potassium chloride and potassium sulfate can be used directly from mining as they contain soluble ions. Phosphate rock is insoluble, so it needs processing: reacting with nitric acid (makes calcium nitrate & phosphoric acid), sulfuric acid (makes single superphosphate), or phosphoric acid (makes triple superphosphate). These products are then often neutralized by ammonia to make usable fertilizers.
Industrial production of NPK (nitrogen, phosphorus, potassium) fertilizers is a continuous, large-scale, automated process with high production speed, using raw materials. Laboratory methods are batch processes, small-scale, labor-intensive, slow, and use purchased reactants. For example, ammonium sulfate (ammonia + sulfuric acid) can be made in the lab via titration (since reactants are soluble) or industrially as a continuous process using raw materials for both ammonia and sulfuric acid. A lab experiment for ammonium sulfate involves titrating dilute sulfuric acid with dilute ammonia using an indicator, then evaporating the solution to crystallize the salt.