enthalpy terms

• Standard Conditions

  all values have to be measured uunder an agreed set of conditions

  • 100 kPa - this is the same as 100000 Pa (0.986 atm)
  • 273 K - 0 celsius

  standard conditions are given the plimsoll line symbol

  a thermodynamic reation includes both the balanced chemical equation and enthalpy data
• Enthalpy change of reaction ∆rHӨ

  is the energy change associated with a given reaction
• Enthalpy change of formation ∆fHӨ

  is the energy change that takes place when 1 mole of a compound is formed from its constituent elements in their standard state under standard conditions
• Enthalpy change of combustion ∆cHӨ

  is the energy change that takes place when 1 mole of a substance is completely combusted in their standard state under standard conditions
• Enthalpy change of neutralisation ∆nHӨ

  is the energy change associated with the formation of 1 mole of water form a neutralisation reaction
• In endothermic reactions, more energy is needed to break bonds than to make new ones.

  Therefore, the overall ∆H is positive and heat is taken in from the surroundings.
• In exothermic reactions, the opposite is true, with more energy being needed to make new

  bonds than break existing ones. Therefore, heat is given out and ∆H is negative.