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.
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…