enthalpy change

• System: everything involved in the reaction; reactants and products

  Surroundings: everything else e.g. container an air
• If heat flows from the system to the surroundings the reaction is exothermic
• If heat flows from the surroundings to the system than the reaction is endothermic.
• Enthalpy change is the heat change at constant pressure
• exothermic reactions have a negative value for enthalpy change ΔH
• endothermic reactions have a positive value for enthalpy change ΔH
• This enthalpy level diagram shows an endothermic reaction