7. Enthalpy of formation

The enthalpy of formation is the energy released or absorbed when the compound is formed from its elements, the compound and elements all being at Tref (298.15 K or 25 C) and Pref (1atm). It is symbolized by.

 8. Adiabatic flame temperature

The temperature that can be achieved by the product in the limit of adiabatic operation of the reactor is called the adiabatic flame temperature or adiabatic combustion temperature. It can be determined by use of the conservation of mass and conservation of energy principles. Let us suppose that the combustion air and the combustion products each form ideal gas mixtures. Then the energy rate balance on a per mole of fuel basis gives following relation.

 hp = hR

Enthalpy of product = enthalpy of reactants

That is


Where, i denotes the incoming air and fuel and e the exiting combustion products. The adiabatic temperature varies from the start to the end of the burning process. Hence the adiabatic flame temperature is not constant during the burning period. Itís hard to calculate the adiabatic temperature in the real time. So for the calculation is done assuming that the burning is take place at once and the reactants are in 298 K and 1atm pressure all the time. Also, the content of the firewood, C, O2, N2 etc. are in stable state.