Energetics

• Enthalpy change

  Change in energy during a reaction at constant pressure
• Activation energy- minimum amount of energy required to begin breaking bonds and start a chemical reaction
• Standard enthalpy change of formation


  Enthalpy change when 1 mole of a compound is formed from its elements under standard states and conditions
• Standard enthalpy change of combustion


  Enthalpy change when 1 mole of a substance is completely burned in oxygen and released under standard conditions
• Standard enthalpy change of neutralisation


  Enthalpy change when 1 mole of an acid and an alkali react together under standard conditions to form 1 mole of water
• Hess' law: Total enthalpy change is independent of the route which the chemical reaction takes place
• Standard conditions: temperature 298K, pressure 100kPa, solutions 1moldm-3
• Bond breaking

  • Endothermic
• Bond making

  • Exothermic
• Bond Enthalpy

  The Enthalpy change that takes place when breaking by homolytic fission 1 mol of a given bond in the molecule of a gaseous species
• Standard Enthalpy change of reaction 


  Enthalpy change when the reaction occurs in the molar quantities shown in the chemical equation