A2 Definitions

• Standard Lattice Enthalpy 


  The enthalpy change when one mole of an ionic compound is converted into gaseous ions
• Standard Enthalpy Change of Atomisation

  The enthalpy change when one mole of gaseous atoms is formed from an element in its standard state
• Bond Dissociation Enthalpy 


  The energy required to break one mole of a covalent bond under standard conditions
• First Electron Affinity


  The enthalpy change when one mole of gaseous atoms is converted to one mole of gaseous ions with a single negative charge
• Second Electron Affinity


  The enthalpy change when one mole of gaseous ions with a single negative charge is converted to an ion with a double negative charge
• Enthalpy of Solution


  The enthalpy change when one mole of a solution dissolves in water
• Enthalpy of Hydration


  The enthalpy change when one mole of gaseous ions is converted into one mole of aqueous ions
• Standard Enthalpy Change of Formation

  The enthalpy change when one mole of a compound is formed from its elements under standard condition
• First Ionisation Energy


  The enthalpy change when one mole of gaseous atoms is converted to gaseous ions with a single positive charge
• Entropy


  A measure of disorder
• Feasible Reaction


  free energy, ΔGθ must be negative (<0)
• Free Energy Change


  ΔG = ΔH - TΔS
• Rate of Reaction


  The change in concentration of reactant or product with respect to time
• Rate Constant 


  The proportionality constant that links rate of reaction to the concentrations in the rate equation
• Order of a Reaction

  With respect to a particular reactance is the power to which the concentration of this reaction is raised in the rate equation
• Overall Order


  A reaction is the sum of the powers to which the concentration terms are raised in the rate equation
• Rate Determining Step


  The slowest step in the mechanism of a reaction
• • Brønsted-Lowry Acid


  A proton donor
• • Brønsted-Lowry Base


  A proton acceptor
• Monobasic Acids


  Acids that donate on proton [H+] per molecule of acid
• Acid-Base Equations

  
• Buffer


  A solution that resists changes in pH on addition of small amounts of acid or alkali
• Asymmetrical (chiral) Centre


  An atom that has four different atoms/groups attached
• Optical Isomers


  Molecules that exist as non-superimposable mirror images
• Optically Active 


  A sample which rotates the plane of plane polarised light
• Racemic Mixture


  A 50:50 mixture of two optical isomers
• Nucleophile


  An ion or molecules with a lone pair of electrons that attacks a region of low electron density
• Addition Reaction


  Is one which a π (pi) bond of a double covalent bond is broken and species are added across the bond
• Monoester


  An ester that contains only one ester group
• Transesterfiction


  A reaction where the alkyl group of an ester is exchange with the alkyl group of an alcohol
• Biodiesel


  A fuel, similar to diesel, which is made from vegetable sources e.g. reaction of rapeseed oil with methanol
• Delocalisation (arenes)

  The π electrons are spread over several atoms
• Electrophile 


  An ion or a molecule that attacks areas of high electron density
• Substitution Reaction 


  A reaction where one atom of group is replaced with a different atom or group
• Fragmentation 


  A positively charged ion produced when the molecular ion breaks apart
• Base Peak 


  The peak of greatest abundance in a mass spectrum
• Molecular Ion Peak 


  A peak produced by an ion formed by the removal of one electron from a molecule
• M+1 Peak


  A peak produced by a molecular ion with an increased mass due to the presence of one carbon-13-atom
• Low Resolution NMR Spectrum

  Does to show the spin-spin splitting pattern
• High Resolution NMR Spectrum

  Does show the spin-spin splitting pattern