A2 Chemistry Definitions

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Acid-base pair
A pair of two species that transform into each other by gain or loss of a proton
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Activation energy
The minimum energy required to start a reaction by breaking of bonds
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Adsorption
The process that occurs when a gas, liquid or solute is held to the surface of a solid or, more rarely a, a liquid
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Alicyclic hydrocarbon
A hydrocarbon with carbon atoms joined together in a ring structure
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Aliphatic hydrocarbon
A hydrocarbon with carbon atoms joined together in straight or branched chains
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Alkali
A type of base that dissolves to form hydroxide ions
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Anion
A negatively charged ion
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Average bond enthalpy
The average enthalpy change that takes place when breaking by homiletic fission 1 mol of a given type of bond in the molecules of a gaseous species
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Biodegradable substance
A substance that is broken down naturally in the environment by other living organisms
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Biodegradable polymer
A polymer that breaks down completely into carbon dioxide and water
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Boltzmann distribution
A diagram showing the distribution of energies of the molecules at a particular temperature
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Bond dissociation enthalpy
The enthalpy change that takes place when breaking by homiletic fission 1 mol of a given bond in the molecules of a gaseous species
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Bronsted-Lowry acid
A species that is a proton donor
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Bronsted-Lowry base
A species that is a proton acceptor
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Buffer solution
A system that minimises pH changes on addition of small amounts of an acid or a base
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Carbanion
An organic ion in which a carbon atom has a negative charge
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Carbocation
An organic ion in which a carbon atom has a positive charge
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Catalyst
A substance that increases the rate of a chemical reaction without being used up in the process
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Chemical shift
A scale that compares the frequency of an NMR absorption with the frequency of the reference peak of TMS at δ = 0 ppm
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Chiral carbon
A carbon atom attached to four different atoms or groups of atoms
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Chromatogram
A visible record showing the result of separation of the compounds of a mixture by chromatography
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Complex ion
A transition metal ion bonded to one or more ligands by coordinate bonds
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Conjugate acid
A species formed when a proton is added to a base
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Conjugate base
A species formed when a proton is added to an acid
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Coordinate bond
A shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only
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Coordination number
The total number of coordinate bonds formed between the central metal ion and any ligands
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Degradable polymer
A polymer that breaks down into smaller fragments when exposed to light, heat or moisture
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Dehydration
An elimination reaction in which water is removed from a saturated molecule to make an unsaturated molecule
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Displacement reaction
A reaction in which a more reactive element displaces a less reactive element from an aqueous solution of its ions
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(First) electron affinity
The enthalpy change required to add one electron to each atom in mole of gaseous 1 ions to form one mole of gaseous 1- ions
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(Second) electron affinity
The enthalpy change required to add one electron to each ion on one mole of gaseous 1- ions to form one mole of gaseous 2- ions
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Electronegativity
A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond
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Electrophile
An atom which is attracted to an electron-rich centre or atom, where it accepts a pair of electrons to form a new covalent bond
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Elimination reaction
The removal of a molecule from a saturated molecule to make an unsaturated molecule
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Enantiomers
Stereoisomers that are non-superimposable mirror images of each other (optical isomers)
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End point
The point in a titration at which there are equal concentrations of the weak acid and conjugate base forms of the indicators. The colour at the end point is midway between the colours of the acid and conjugate base forms
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(Standard) enthalpy change of atomisation
The enthalpy change that takes place when one mole go gaseous atoms forms from the elements in its standard state
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(Standard) enthalpy change of combustion
The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, all reactants and products being in their standard states
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(Standard) enthalpy change of formation
The enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states under standard conditions
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(Standard) enthalpy change of hydration
The energy change that takes place when one mole of isolates gaseous ions is dissolved in water, forming one mole of aqueous ions, under standard conditions
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(Standard) enthalpy change of neutralisation
The energy change that accompanies the neutralisation of an aqueous acid by an aqueous base to form one mole of water, under standard condtions
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(Standard) enthalpy change of solution
The enthalpy change that takes place when one mole of a compound is completely dissolved in water under standard conditions
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Enthalpy cycle
A diagram showing alternative routes between reactants and products that allows the indirect determination of an enthalpy change from other known enthalpy changes using Hess's law
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Enthalpy profile diagram
A diagram for a reaction to compare the enthalpy of the reactants with th enthalpy of the products
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Enthalpy, H
The heat that is stored in a chemical system
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Entropy, S
The quantitative measure of the degree of disorder in a system
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(Standard) entropy change of a reaction
The entropy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states
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Equivalence point
The point in a titration at which the volume of one solution has reacted exactly with the volume of the second solution
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Free energy change, ΔG
The balance between enthalpy, entropy and temperature for a process: ΔG = ΔH – TΔS. A process can take place spontaneously when ΔG < 0
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Half-life
The time taken for the concentration of a reactant to reduce by half
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Hess’s Law
A reaction in which the catalyst has a different physical state from the reactants; frequently reactants are gases whilst the catalyst is a solid
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Heterogeneous catalysis
A reaction in which the catalyst has a different physical state from the reactants; frequently reactants are gases whilst the catalyst is a solid
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Heterogeneous equilibrium
An equilibrium in which the species making up the reactants and products are in different physical states
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Heterolytic fission
The breaking of a covalent bond with both of the bonded electrons going to each atom, forming a cation (+ ion) and an anion (– ion)
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High-density lipoprotein (HDL)
A type of lipoprotein that can remove cholesterol from the arteries and transport it back to the liver for excretion or re-utilisation
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Homogeneous catalysis
A reaction in which the catalyst and reactants are in the same physical state, which is most frequently the aqueous or gaseous state
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Homogeneous equilibrium
An equilibrium in which all the species making up the reactants and products are in the same physical state
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Homolytic fission
The breaking of a covalent bond with one of the bonded electrons going to each atom, forming two radicals
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Hydrated
A crystalline compound containing water molecules
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Initial rate of reaction
The change in concentration of a reactant or product per unit time at the start of the reaction: t = 0
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Intermediate
A species formed in one step and used up in a subsequent step and so never seen as either a reactant or a product
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Intermolecular force
An attractive force between neighbouring molecules. Intermolecular forces can be van der Waals’ forces, dipole–dipole forces or hydrogen bonding
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(First) ionisation energy
The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions
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(Second) ionisation energy
The energy required to remove one electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions
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Isoelectric point
The point at which an amino acid has no overall charge
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Isotopes
Atoms of the same element with different numbers of neutrons and different masses
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Lattice enthalpy
The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions
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Le Chatelier’s Principle
When a system in dynamic equilibrium is subjected to a change, the system readjusts itself to minimise the effect of the change and to restore equilibrium
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Ligand
A molecule or ion that can donate a pair of electrons to a transition metal ion
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Ligand substitution
A reaction in which one ligand in a complex ion is replaced by another ligand
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Limiting reagent
The substance in a chemical reaction that runs out first
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Low-density lipoprotein (LDL)
A type of lipoprotein responsible for carrying cholesterol and triglycerides from the liver to the tissues
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Mobile phase
The phase that moves in chromatography
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Molecular ion, M+
The positive ion formed in mass spectrometry when a molecule loses an electron
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Neutralisation
A chemical reaction in which an acid and a base react together to produce a salt and water
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Nucleophile
An atom (or group of atoms) which is attracted to an electron-deficient centre or atom, where it donates a pair of electrons to form a new covalent bond
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Optical isomers
Stereoisomers that are non-superimposable mirror images of each other; also called ‘enantiomers’
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Order
The power to which the concentration of the reactant is raised in the rate equation
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Overall order
The sum of the individual orders: m + n
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Peptide
A compound containing amino acids linked by peptide bonds. Often the number of amino acids is indicated by the prefix, di-, tri-, tetra-: dipeptide = 2 amino acids tripeptide = 3 amino acids tetrapeptide = 4 amino acids
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pH
pH = –log[H+(aq)] [H+(aq)] = 10–pH
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Pharmacological activity
The beneficial or adverse effects of a drug on living matter
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Phase
A physically distinctive form of a substance, such as the solid, liquid and gaseous states of ordinary matter
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Rate constant, k
The constant that links the rate of reaction with the concentrations of the reactants raised to the powers of their orders in the rate equation
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Rate equation
For a reaction: A + B → C, the rate equation is given by: rate = k[A]m[B]n. m is the order of reaction with respect to A. n is the order of reaction with respect to B. (m + n = overall order)
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Rate of reaction
The change in concentration of a reactant or a product in a given time
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Rate-determining step
The slowest step in a multi-step reaction
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Retention time
The time for a component to pass from the column inlet to the detector
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Spin–spin coupling
The interaction between spin states of non-equivalent nuclei that results in a group of peaks in an NMR spectrum
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Stability constant, Kstab
The equilibrium constant for an equilibrium existing between a transition metal ion surrounded by water ligands and the complex formed when the same ion has undergone a ligand substitution reaction
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Standard conditions
A pressure of 100 kPa (1 atmosphere), a stated temperature, usually 298 K (25 °C) and a concentration of 1 mol dm–3 (for reactions with aqueous solutions)
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Standard electrode potential
The e.m.f. of a half-cell compared with a standard hydrogen half-cell, measured at 298 K with solution concentrations of 1 mol dm–3 and a gas pressure of 101 kPa (1 atmosphere)
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Stationary phase
The phase that does not move in chromatography
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Strong acid
An acid that completely dissociates in solution
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Transition element
A d-block element which forms an ion with an incomplete d sub-shell
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Weak acid
An acid that partially dissociates in solution
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Zwitterion
A dipolar ionic form of an amino acid that is formed by the donation of a hydrogen ion from the carboxyl group to the amino group. As both charges are present there is no overall charge
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Other cards in this set

Card 2

Front

The minimum energy required to start a reaction by breaking of bonds

Back

Activation energy

Card 3

Front

The process that occurs when a gas, liquid or solute is held to the surface of a solid or, more rarely a, a liquid

Back

Preview of the back of card 3

Card 4

Front

A hydrocarbon with carbon atoms joined together in a ring structure

Back

Preview of the back of card 4

Card 5

Front

A hydrocarbon with carbon atoms joined together in straight or branched chains

Back

Preview of the back of card 5
View more cards

Comments

normanp

card 8, homolytic fission

sophiehurst12345

Card 51 which is Hess's Law should be "the total enthalpy change of a reaction is always the same, no matter which route is taken"

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