Definitions AS2 Flashcards
Empirical Formula
A formula which shows the simplest whole number ratio of atoms of each element in a compound.
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 e.g. 24dm3 at 20°C and one atmosphere pressure.
Percentage yield
Shows how much product was actually made compared with the amount of product that was expected.
Theoretical yield.
The maximum mass of product expected from the reaction, using reacting masses.
Actual yield.
The mass of the product that is actually obtained from the real chemical reaction.
Homologous Series
Compounds with the same general formula
Similar chemical properties
Shows a gradation in physical properties
Successive members differ by CH2 unit
Functional group
Reactive group within a compound
Structural Isomers
Molecules which have the same molecular formula but different structural formula.
Geometric isomers/stereoisomers
Molecules with the same structural formula, but different arrangement of atoms due to the presence of one or more carbon double bonds.
Saturated hydrocarbon
Contains no double carbon bonds.
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 a shared pair go to a single atom.
Radical
A particle with an unshared electron.
Sigma bond
A covalent bond formed by the 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.
Hydrogenation
Addition of a hydrogen molecule across a carbon double bond
Electrophile
An ion or molecule that attacks regions of high electron density.
Primary carbocation
A carbocation which has a 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.
Polymerisation
Joining together of many small molecules to form a large molecule.
Monomers
Many small molecules that join together to form a polymer.
Polymer
A large molecule when many small monomers join together.
Primary/secondary/tertiary halogenoalkane
A halogenoalkane which has one/two/three carbon atom directly bonded to the carbon atom that is bonded to the halogen.
Reflux
Repeated boiling and condensing of a mixture.
Hydrolysis
Breaking up molecules with reaction of 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 larger molecule.
Miscibility
Liquids that mix in all proportions i.e. form a single layer.
Primary/secondary/tertiary alcohol
An alcohol which has one/two/three carbon atom(s) 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.
Addition polymerisation
Joining together of many small monomer molecules to form a large molecule with no loss of any part of molecule.
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 that of the reactants.
Exothermic
A reaction in which the enthalpy of the products is less that the enthalpy of reactants.
Standard conditions.
298K and 100kPa
Standard enthalpy change.
Change in heat energy at constant pressure, measured at 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.
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 of a reactant or product with respect to time.
Catalyst
A substance with increases the rate of a chemical reaction but doesn’t 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
Rate of forward reaction is equal to the rate of 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
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-subshell (orbital)
Solubility
The maximum mass of solute that will dissolve in 100g of solvent at a stated temperature.
