Module 3

• 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.
• bond enthalpy


  The enthalpy change that takes place when breaking by homolytic fission 1 mol of a given bond in the molecules of a gaseous species.
• 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 (∆H +ve).
• enthalpy, H


  The heat content that is stored in a chemical system.
• (standard) enthalpy change of combustion, ∆Hcө

  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.
• (standard) enthalpy change of formation, ∆Hfө

  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.
• (standard) enthalpy change of reaction, ∆Hrө

  The enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states.
• enthalpy profile diagram


  A diagram for a reaction to compare the enthalpy of the reactants with the enthalpy of the products.
• 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 (∆H -ve).
• Standard conditions

  (298K 100KPa)
• Closed System


  Sealed reaction. nothing can enter nor leave
• dynamic equilibrium


  both the forward and reverse reactions are taking place at the same rate.