Energetics

Enthalpy Change 

of a system is the heat energy change at constant pressure. 
      The symbol for enthalpy change is (delta) H.

Exothermic- system gives out heat energy to its surroundings.
            Enthalpy is lost by the system.
    (Delta) H is negative. 

Endothermic- system takes in heat energy from the surroundings.
      Enthalpy is gained by the system.
        (Delta) H is positive.

Standard Conditions: Pressure- 100kPa.
  Temperature- 298K 

Elements and compounds are said to be in their standard state. Eg Oxygen (gas), Water (l).

Standard Enthalpy Change of Combustion- is defined as the enthalpy change, under standard conditions when 1 mol of a substance is burned completely in oxygen, with all reactants and products in their standard states.

Enthalpies of combustion are determined experimentally using a calorimeter.  (see further…