BGCSE Chemistry 0570 flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Diffusion

The net movement of particles from a region of higher concentration to a region of lower concentration, caused by random motion; it is faster at higher temperature and for lighter particles.

Brownian motion

The random, jerky movement of small particles such as smoke grains suspended in a fluid, caused by unbalanced collisions with faster-moving fluid particles; it provides evidence for particle motion.

Melting point

The constant temperature at which a solid changes to a liquid; during melting, energy supplied breaks the lattice rather than raising the temperature.

Kinetic theory of gases

A model in which gas particles move rapidly and randomly, colliding with each other and with container walls; these collisions create pressure that rises with temperature and falls with volume.

Mass number

The total number of protons and neutrons in the nucleus of an atom; the number of neutrons is found by subtracting the atomic number from the mass number.

Isotopes

Atoms of the same element with the same number of protons but different numbers of neutrons; they have identical chemical properties but different masses and physical behaviour.

Ionic bonding

Electrostatic attraction between oppositely charged ions formed when a metal transfers electrons to a non-metal; the ions form a giant lattice with high melting point.

Covalent bond

A bond formed when two non-metal atoms share one or more pairs of electrons; simple molecular substances have weak intermolecular forces and low melting points.

Mole

The amount of substance containing 6.02 x 10^23 particles; the mass of one mole in grams equals the relative atomic or molecular mass.

Empirical formula

The simplest whole-number ratio of atoms of each element in a compound, found by dividing each element's mass or percentage by its relative atomic mass.

Neutralisation

The reaction between an acid and a base producing a salt and water; in terms of ions, hydrogen ions and hydroxide ions combine to form water.

Collision theory

The idea that a reaction occurs only when particles collide with at least the activation energy and correct orientation; raising temperature, concentration or surface area increases successful collisions.

Electrolysis

The breakdown of an ionic compound by passing electricity through it when molten or in aqueous solution; cations go to the cathode and anions to the anode.

Oxidation

The loss of electrons by a substance, or the gain of oxygen; an oxidising agent accepts electrons and is itself reduced during the reaction.

Exothermic reaction

A reaction that releases energy to the surroundings, usually shown by a temperature rise; the energy released in bond making exceeds that needed for bond breaking.

Le Chatelier's principle

When a system at equilibrium is disturbed by a change in temperature, pressure or concentration, the position of equilibrium shifts to oppose that change.

Reactivity series

A list of metals in order of decreasing reactivity; metals above carbon are extracted by electrolysis, while those below carbon are reduced with carbon.

Alloy

A mixture of a metal with other elements; the different-sized atoms prevent layers sliding over each other, making the alloy harder and stronger than the pure metal.

Alkene

An unsaturated hydrocarbon containing a carbon-carbon double bond with general formula CnH2n; it decolourises bromine water, distinguishing it from an alkane.

Cracking

The breakdown of long-chain hydrocarbons into shorter, more useful alkanes and alkenes by heating with a catalyst; it produces alkenes for making polymers.

Greenhouse gases

Gases such as carbon dioxide and methane that absorb infrared radiation emitted by the Earth and re-emit it, contributing to warming of the atmosphere.

Acid rain

Rain made acidic by sulfur dioxide and nitrogen oxides released from burning fossil fuels; it damages buildings, soils, lakes and plants.

Burette

A long graduated tube with a tap used to deliver accurate, variable volumes of liquid, typically in a titration; readings are taken from the bottom of the meniscus.

Rf value

In chromatography, the distance moved by a spot divided by the distance moved by the solvent front; it is constant for a substance under fixed conditions.

Relative atomic mass

The weighted mean mass of the atoms of an element compared with one-twelfth of the mass of a carbon-12 atom, taking isotope abundances into account.

Giant covalent structure

A network of atoms joined by covalent bonds throughout the substance, as in diamond and silicon dioxide, giving very high melting points and great hardness.

Molar gas volume

The volume occupied by one mole of any gas, about 24 dm3 at room temperature and pressure; moles of gas equal volume in dm3 divided by 24.

Catalyst

A substance that increases the rate of a reaction by providing an alternative pathway with lower activation energy, and is chemically unchanged at the end.

Electroplating

Coating an object with metal by electrolysis, using the object as the cathode, the plating metal as the anode and a solution of the plating metal's salt as electrolyte.

Activation energy

The minimum energy that colliding particles must possess for a reaction to occur; a catalyst lowers it, allowing more collisions to be successful.

Blast furnace

A furnace in which iron is extracted from haematite by reduction with carbon monoxide, using coke, limestone and hot air, producing impure molten iron.

Fractional distillation

Separation of liquids with different boiling points by repeated vaporisation and condensation in a fractionating column; used to refine crude oil into fractions.

Water of crystallisation

Water chemically combined in a hydrated salt in a fixed ratio; it is removed by heating, and the mass lost gives the ratio of water to anhydrous salt.