SACE Stage 2 Chemistry key terms

Rain, snow or fog that has become acidic because sulfur dioxide and nitrogen oxides from burning fossil fuels dissolve in water to form sulfuric and nitric acids, damaging soils, lakes and buildings.

A gas in the atmosphere, such as carbon dioxide, methane or water vapour, that absorbs infrared radiation emitted by Earth's surface and re-emits it, slowing the loss of heat to space and warming the planet.

An analytical technique that measures how much light of a specific wavelength a vaporised sample absorbs, allowing the concentration of a particular metal ion in a water or soil sample to be determined.

A graph plotted from measurements of standard solutions of known concentration, used to convert the instrument response for an unknown sample into a reliable concentration value.

A concentration unit meaning one part of a substance in one million parts of the mixture; for dilute aqueous solutions it is roughly equivalent to one milligram of solute per litre of solution.

A measure of the oxygen used by microorganisms as they break down organic matter in a water sample over a set period, indicating the level of organic pollution present.

The enrichment of a waterway with nutrients such as nitrates and phosphates, which triggers rapid algal growth; when the algae die, decomposition consumes dissolved oxygen and other organisms may suffocate.

The process in which a persistent substance that dissolves in fat, such as mercury or DDT, becomes more concentrated at each step of a food chain because it is not excreted or broken down.

A brownish haze that forms when sunlight reacts with nitrogen oxides and volatile organic compounds in the air, producing ozone and other irritant pollutants, especially over cities on still, sunny days.

The state of a closed system in which the forward and reverse reactions continue at equal rates, so the concentrations of reactants and products remain constant even though both reactions are still occurring.

When a change in conditions, such as temperature, pressure or concentration, is imposed on a system at equilibrium, the position of equilibrium shifts in the direction that partly opposes the change.

The ratio, at equilibrium and at a stated temperature, of the product of product concentrations to the product of reactant concentrations, each raised to the power of its coefficient in the balanced equation.

The model stating that a reaction occurs only when particles collide with enough combined kinetic energy and with suitable orientation, so increasing concentration, pressure, surface area or temperature usually speeds up reactions.

The minimum extra energy that colliding particles must have for a reaction to take place; it corresponds to the energy barrier between reactants and products on an energy profile diagram.

A substance that increases the rate of a reaction by providing an alternative pathway with lower activation energy, without being consumed overall or changing the position of equilibrium.

The mass of product actually obtained expressed as a percentage of the theoretical maximum mass calculated from the balanced equation, showing how efficiently the reaction was carried out.

The set of temperature, pressure and catalyst choices used in an industrial process that balances conflicting requirements, such as fast rate versus high yield, to give the most economic overall result.

A reaction that releases energy to its surroundings, usually as heat, because the products contain less chemical energy than the reactants; the temperature of the surroundings rises.

An atom or small cluster of atoms within a molecule that gives the compound its characteristic chemical properties and reactions, such as the hydroxyl group in alcohols or the carboxyl group in acids.

A family of organic compounds with the same functional group and general formula, in which successive members differ by one CH2 unit and show a gradual trend in physical properties.

One of two or more molecules that have the same molecular formula but different arrangements of atoms, giving different physical properties and often different chemical behaviour.

A reaction in which two molecules join to form a single product with no atoms lost; alkenes commonly undergo this when the double bond opens and two new single bonds form.

A reaction in which two molecules combine with the loss of a small molecule such as water or hydrogen chloride; it links monomers together to form polyesters, polyamides and peptides.

The breaking of a chemical bond by reaction with water, commonly used to split esters into an alcohol and a carboxylic acid, or proteins into amino acids.

The reversible reaction of a carboxylic acid with an alcohol, catalysed by acid, that produces an ester and water and is responsible for the pleasant smells of many fruits and flavourings.

The joining of many unsaturated monomer molecules, such as ethene, into a long chain polymer in which no other product is formed and the monomers are linked by single bonds.

An organic molecule containing both an amine group and a carboxyl group attached to the same carbon; about twenty different ones are joined in chains to build proteins.

The amide link formed when the carboxyl group of one amino acid reacts with the amine group of another, releasing water and creating the chain that forms the backbone of proteins.

A salt of a long-chain fatty acid whose molecules have a water-loving head and a fat-loving tail, allowing them to bridge oil and water and lift grease into water as tiny droplets.

The anaerobic breakdown of sugars by microorganisms or enzymes to produce ethanol and carbon dioxide, or lactic acid, used in brewing, winemaking and bread making.

A natural resource that is replenished by natural processes at a rate comparable to its use, such as solar energy, wind, biomass or fresh water, so it can be relied on in the long term.

A carbon-based fuel such as coal, petroleum or natural gas formed from the remains of ancient organisms over millions of years, which is burned for energy and is not replaced on a human timescale.

A fuel produced from recently living plant or animal material, for example ethanol from sugarcane or biodiesel from vegetable oil, which is considered renewable because the feedstock can be regrown.

The heat energy released when one mole of a substance is completely burned in excess oxygen under standard conditions, usually measured with a calibrated calorimeter and quoted in kilojoules per mole.

Burning that occurs when oxygen is limited, producing carbon monoxide, soot and sometimes unburned hydrocarbons instead of only carbon dioxide and water, wasting energy and creating toxic pollution.

A device that generates electrical energy by the controlled electrochemical reaction of a fuel, often hydrogen, with oxygen, producing water as the only product and operating continuously while fuel is supplied.

A structured method of estimating the total environmental impact of a product from extracting raw materials, through manufacture and use, to disposal or recycling, so alternatives can be compared fairly.

Using resources and running processes in ways that meet present needs without depleting stocks or damaging ecosystems so that future generations can meet their own needs.