CCEA- Chemistry- AS2 Terms

empirical formula

a formula which shows the simplest whole number ratio of atoms of each element in a commpound

molecular formula

a formula which shows the actual number of atoms of each element in a molecule

molar gas volume

the volume of one mole of gas under specified conditions of temperature and pressure

percentage yield

actual yield/theoretical yield x 100

atom economy

mass of desired product/total mass of products x 100

homologous series

compounds which have the same general formula, similar chemical properties, show a gradation in physical properties and successive members differ by a CH2 unit

functional group

reactive group within a compound

structural isomers

molecules which have the same molecular formula but a different structural formula

geometric isomers

molecules with the same structural formula, but different arrangement of atoms due to the presence of one or more C=C bond

saturated hydrocarbon

contains no C=C or C triple bond C bond.

hydrocarbon

contains hydrogen and carbon only

substitution

replacing one atom or group with a different atom or group

homolytic fission

bond breaking in which one of the shared electrons goes to each atom

heterolytic fission

bond breaking in which both electrons in the shared pair go to a single atom

radical

a particle with an unpaired electron

unsaturated hydrocarbon

contains at least one C=C or C triple bond C bond.

sigma bond

a covalent bond caused by linear overlap of atomic orbitals

pi bond

a covalent bond formed by the sideways overlap of p orbitals

bond length

the distance between the nuclei of two covalently bonded atoms

polymerisation

joining together of many small molecules to form a large molecule

monomers

many small molecules which join together to form a polymer

polymer

a large molecule formed when monomers join together

primary halogenoalkane

a halogenoalkane which has one carbon atom directly bonded to the carbon atom that is bonded to the halogen. (exceptions are halomethanes)

secondary halogenoalkane

a halogenoalkane which has 2 carbon atoms directly bonded to the carbon atom that is bonded to the halogen

tertiary halogenoalkane

a halogenoalkane which has 3 carbon atoms directly bonded to the carbon atom that is bonded to the halogen

reflux

repeated boiling and condensation of a (reaction) mixture

hydrolysis

breaking up molecules by reaction with water

nucleophile

an ion or molecule, with a lone pair of electrons, that attacks regions of low electron density

elimination

a reaction in which a small molecule is removed from a large molecule

electrophile

an ion or molecule that attacks regions of high electron density

hydrogenation

addition of hydrogen molecule across a C=C

primary carbocation

a carbocation which has one carbon atom directly bonded to the positively charged carbon

secondary carbocation

a carbocation which has two carbon atoms directly bonded to the positively charged carbon

tertiary carbocation

a carbocation which has three carbon atoms directly bonded to the positively charged carbon

miscibility

liquids which mix in all proportions ie. form a single layer

primary alcohol

an alcohol which has one carbon atom directly bonded to the carbon atom that is bonded to the -OH group. (Exception is methanol)

secondary alcohol

an alcohol which has two carbon atoms directly bonded to the carbon atom that is bonded to the -OH group

tertiary alcohol

an alcohol which has three carbon atoms directly bonded to the carbon atom that is bonded to the -OH group

ground state

a molecular vibration which is in the lowest possible energy state

wavenumber

the reciprocal of the wavelength and it is measured in cm-1

endothermic

a reaction in which the enthalpy of the products is greater than the enthalpy of the reactants

exothermic

a reaction in which the enthalpy of the products is less than the enthalpy of the reactants

standard conditions

298K and 100kPa

standard enthalpy change

change in heat energy at constant pressure, measured in standard conditions

standard enthalpy of combustion

the enthalpy change when one mole of a substance is completely burnt in oxygen under standard conditions

standard enthalpy of formation

the enthalpy change when one mole of a compound is formed from its elements under standard conditions

standard enthalpy of neutralisation

the enthalpy change when one mole of water is produced in a neutralisation reaction under standard conditions

conservation of energy

energy cannot be created or destroyed but it can change from one form to another

hess's law

the enthalpy change for a reaction is independent of the route taken, provided the initial and final conditions are the same

average bond enthalpy

the energy required to break one mole of a given bond averaged over many compounds

reaction rate

the change of the concentration (amount) of a reactant or product with respect to time

catalyst

a substance which increases the rate of reaction but does not get used up.

activation energy

the minimum amount of energy required for a reaction to occur

reversible

a reaction which goes in both the forward and backward directions

dynamic equilibria

rate of forward reaction is equal to the rate of the backward reaction

equilibrium

a reversible reaction in which the amount of each reactant/product remains constant

homogenous

a reaction in which all the reactants and products are in the same physical state

heterogenous equilibria

a reaction in which all the reactants and products are not in the same state

heterogenous catalyst

the catalyst is in a different phase from the reactants

s-block element

an element which has an atom with highest energy/outer electron in an s-shell orbital

solubility

the maximum mass of solute that will dissolve in 100g of solvent at a stated temperature

Kc

Kc = [C]c[D]d

[A]a[B]b

aA + bB --> cC + dD