definitions

• entropy

  the degree of disorder within a system
• free energy

  the total amount of energy available to do work
• standard enthalpy of formation

  the enthalpy change when one mole of a substance is removed from its elements in their standard states
• standard state

  the most stable state of a substance under standard conditions
• standard conditions

  refer to a pressure of one atmosphere and a temperature of 298 K
• first law of thermodynamics

  energy cannot be created or destroyed - it can only be transferred or transformed
• second law of thermodynamics

  the total entropy of a reaction and it's surroundings always increases for a spontaneous change - for a reaction to be feasible, entropy change must be positive
• third law of thermodynamics

  the entropy of a perfect crystal at 0 K is zero
• atomic orbital

  a region of space around the nucleus of an atom where there is a high probability, around 90%, of finding an electron
• buffer solution

  a solution in which the pH remains approximately constant when small amounts of acid or base are added
• acid

  a proton donor
• base

  a proton acceptor
• agonist

  a drug which mimics or enhances the body's natural response
• antagonist

  a drug which blocks the body's natural response
• amphoteric

  a substance that can act as both an acid and a base
• aufbau principle

  electrons fill orbitals in order of increasing energy, they occupy lowest energy orbitals first before filling orbitals of higher energy
• aromatic compounds

  compounds that contain a planar ring of conjugated bonds with a delocalized electron system
• carbocation

  an ion with a positively charged carbon atom
• chiral

  a central carbon atom with 4 different atoms or groups bonded to it
• closed system

  theres no exchange of matter or energy with its surroundings
• conjugate acid

  the species left when a base accepts a proton
• conjugate base

  the species left when an acid donates a proton
• conjugated system

  a system in which alternating single and double bonds occur, allowing for the delocalization of electrons across adjacent atoms in the molecule
• co-ordination number

  the number of bonds a transition metal ion forms with surrounding ligands
• dative bond

  a covalent bond where both electrons have come from one of the elements involved in the bond
• degenerate

  in equal energy
• dynamic equilibrium

  when the rate of the forward and reverse reaction is equal, and the concentration of reactants and products are constant
• electromagnetic spectrum

  the range of frequencies or wavelengths of electromagnetic radiation
• electrophile

  an electron deficient molecule that seek to gain electrons, usually positively charged
• nucleophile

  electron rich species that seek to donate a pair of electrons, usually negatively charged
• enantiomers

  a pair of optical isomers
• frequency

  the number of wavelengths that pass a fixed point in one unit of time
• wavelength

  the distance between adjacent crests
• ground state

  the lowest possible electronic configuration the electrons in an atom can adopt
• hund's rule

  electrons fill degenerate orbitals singly, before pairing with opposite spins
• ionisation energy

  the energy required to remove one mole of electrons from one mole of atoms in a gaseous state
• ligand

  a molecule or ion that donates a pair of electrons to a central metal atom or ion to form a dative bond
• pauli's exclusion principle

  no two electrons in an atom can have the same set of quantum numbers, and they must have opposite spins
• racemic mixture

  an optically inactive mixture which contains equal concentrations of both optical isomers
• the rate determining step

  the slowest step in a reaction mechanism that determines the overall rate of reaction