Thermochemistry (2.1)

• What is the principle of the conservation of energy?

  Energy cannot be created or destroyed, only transformed from form to another 
• What are Standard conditions?

  Pressure: 1 atmosphere

  Temp: 25°c
• What is the 'system'?

  The collection of substances involved in the chemical reaction
• What is Hess's law?

  If a reaction can occur by more than one route, the total energy change for the reaction is independent of the route taken
• Formula for enthalpy change of formation


  ΔΗ= Σ ΔΗ° (p) - Σ ΔΗ° (r)
• Formula for enthalpy change of combustion


  ΔΗ= Σ ΔcΗ° (r) - Σ ΔcΗ° (p)
• Formula for direct determination enthalpy change (calorimetry) 


  ΔΗ° = (-mcΔΤ) ÷ n
• What are the conditions to use a colorimeter?

  Must be spontaneous and involve a liquid
• What is enthalpy of combustion? 


  The energy change that takes place when you completely react 1 mole with oxygen under standard conditions
• What are the two reasons why a experiment may give a lower energy result than expected?

  Loss of heat to surroundings

  Don't get complete combustion
• What are the two ways to get a more accurate energy result in an experiment?

  Use an insulating card to minimise heat loss

  Use an oxygen atmosphere to get complete combustion
• Why is a bomb calorimeter more reliable than a spirit burner?

  Better insulated

  Better oxygen surrounding so more complete combustion