Y12 Chemistry Definitions

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Relative isotopic mass
The mass of an isotope relative to 1/12th the mass of carbon-12.
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Relative atomic mass Ar
The weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of carbon-12.
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First ionisation energy
The energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions.
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Enthalpy change of combustion ΔcH
The enthalpy change that takes place when one mole of a substance reacts completely with oxygen
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Enthalpy change of formation ΔfH
The enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states
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Enthalpy change of neutralisation ΔneutH
The enthalpy change that accompanies the reaction of an acid by a base to form one mole of H2O(l)
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Standard conditions
A pressure of 100 kPa, 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 state
The physical state of a substance under standard conditions of 100 kPa and a stated temperature (usually 298 K).
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Standard enthalpy change of combustion ΔcH Θ
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 ΔfH Θ
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 neutralisation ΔnuetH Θ
The enthalpy change that accompanies the reaction of an acid by a base to form one mole of H2O(l), under standard conditions, with all reactants and products in their standard states.
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Homologous series
A series of organic compounds with the same functional group but with each successive member differing by CH2.
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Electrophile
An electron pair acceptor
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Nucleophile
An electron pair donor
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Isotopes
Atoms of the same element with different numbers of neutrons and different masses.
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Relative molecular mass Mr
The weighted mean mass of a molecule of a compound compared with one-twelfth of the mass of an atom of carbon-12.
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Relative formula mass
The weighted mean mass of the formula unit of a compound compared with one-twelfth of the mass of an atom of carbon-12.
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Mole
The amount of any substance containing as many elementary particles as there are carbon atoms in exactly 12 g of the carbon-12 isotope, that is, 6.02 × 10^23 particles
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Molar mass M
The mass per mole of a substance, in units of g mol–1.
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Molar gas volume Vm
The volume per mole of gas molecules at a stated temperature and pressure
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Empirical Formula
The formula that shows the simplest whole-number ratio of atoms of each element present in a compound.
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Molecular Formula
A formula that shows the number and type of atoms of each element present in a molecule.
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Anhydrous
Containing no water molecules.
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Hydrated
A crystalline compound containing water molecules.
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Water of crystallisation
Water molecules that are bonded into a crystalline structure of a compound.
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Atom economy
(Sum of molar masses of desired products)/(sum of molar masses of all products)
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Percentage yield
Actual mass/Theoretical mass x 100%
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Strong acid
An acid that dissociates completely in solution.
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Weak acid
An acid that dissociates only partially in solution.
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Neutralisation
A chemical reaction in which an acid and a base react together to produce a salt.
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Oxidation
Loss of electrons or an increase in oxidation number
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Reduction
Gain of electrons or a decrease in oxidation number.
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Atomic orbital
A region around the nucleus that can hold up to two electrons, with opposite spins.
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Ionic bond
The strong electrostatic attraction between positive and negative ions
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Covalent bond
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.
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Metallic bond
The electrostatic attraction between positive metal ions and delocalised electrons.
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Average bond enthalpy
The average enthalpy change that takes place when breaking by homolytic fission 1 mol of a given type of bond in the molecules of a gaseous species.
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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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Induced dipole-dipole interactions
Attractive forces between induced dipoles in different molecules – also called London Forces.
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Permanent dipole-dipole interactions
An attractive force between permanent dipoles in neighbouring polar molecules.
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Hydrogen bond
A strong dipole-dipole attraction between an electron-deficient hydrogen atom of –NH, –OH or HF on one molecule and a lone pair of electrons on a highly electronegative atom containing N, O or F on a different molecule.
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Oxidising agent
A reagent that oxidises (takes electrons from) another species
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Reducing agent
A reagent that reduces (adds electrons to) another species
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Disproportionation
A redox reaction in which the same element is both oxidised and reduced.
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Endothermic reaction
A reaction in which the enthalpy of the products is greater than the enthalpy of the reactants, resulting in heat being taken in from the surroundings (ΔH is positive).
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Exothermic reaction
A reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings (ΔH is negative).
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Activation energy
The minimum energy required to start a reaction by the breaking of bonds.
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Catalyst
A substance that increases the rate of a chemical reaction without being used up in the process; a catalyst provide an alternative route for the reaction with lower activation energy.
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Homogenous 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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Heterogenous 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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Dynamic equilibrium
The equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction and concentrations do not change.
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Le Chatelier’s principle
When a system in dynamic equilibrium is subjected to a external change, the system readjusts itself to minimise the effect of the change and to restore equilibrium.
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General formula
The simplest algebraic formula for a member of a homologous series
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Displayed formula
A formula showing the relative positioning of all the atoms in a molecule and the bonds between them.
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Structural formula
A formula showing the minimal detail for the arrangement of atoms in a molecule.
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Skeletal formula
A simplified organic formula, with hydrogen atoms removed from alkyl chains, leaving just a carbon skeleton and associated functional groups.
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Functional groups
The part of the organic molecule responsible for its chemical reactions.
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Alkyl group
A side chain formed by removing a hydrogen atom removed from an alkane parent chain, for example, CH3, C2H5; any alkyl group is often shown as R.
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Alicyclic
Containing carbon atoms joined together in a ring that is not aromatic.
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Aliphatic
Containing carbon atoms joined together in straight or branched chains.
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Aromatic
A compound containing a benzene ring.
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Saturated
Containing carbon-carbon single bonds only.
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Unsaturated
Containing a multiple carbon-carbon bond.
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Structural isomers
Molecules with the same molecular formula but with different structural formulae.
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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 (positive ion) and an anion (negative ion).
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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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Radical
A species with an unpaired electron.
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Curly arrow
Movement of an electron pair
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Alkanes
The hydrocarbon homologous series with single carbon-to-carbon bonds and the general formula: CnH2n+2.
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Alkenes
The hydrocarbon homologous series with at one double carbon-to-carbon bonds and the general formula: CnH2n.
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Stereoisomers
Compounds with the same structural formula but with a different arrangement of the atoms in space.
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E/Z isomerism
A type of stereoisomerism in which different groups attached to each carbon of a C=C double bond may be arranged differently in space because of the restricted rotation of the C=C bond.
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Cis-trans isomerism
A special type of E/Z isomerism in which there are two non-hydrogen groups and two hydrogen atoms around the C=C double bond: the cis isomer (Z isomer) has H atoms on each carbon on the same side; the trans isomer (E isomer) has H atoms on each carbo
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Primary alcohol
OH group on a carbon atom at the end of a chain.
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Secondary alcohol
OH group on a carbon atom which is bonded to two other carbon atoms.
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Tertiary alcohol
OH group on a carbon atom which is bonded to three other carbon atoms.
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Rate of reaction
The rate at which the concentration of a reactant, or product, changes
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Card 2

Front

The weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of carbon-12.

Back

Relative atomic mass Ar

Card 3

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The energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions.

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Preview of the back of card 3

Card 4

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The enthalpy change that takes place when one mole of a substance reacts completely with oxygen

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Card 5

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The enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states

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