Fugacity: It is derived from Latin, expressed as fleetness or escaping ...

CHEMICAL REACTION EQUILIBRIUM
Energy change accompanies all chemical reactions. Because of this energy
change the temperature of the products may increase or decrease depending on the
exothermic or endothermic nature of the reaction. The energy change may be
expressed in terms of heat of reaction, heat of combustion and heat of formation.
Heat of reaction is the change in enthalpy of a reaction under pressure of 1.0
atmosphere, starting & ending with all materials at a constant temperature T
Heat of combustion is the heat of reaction of a combustion reaction.
Heat of formation is the heat of reaction of a formation reaction. A formation
reaction is one which results in the formation of one mole of a compound from the
elements.
Eq. H2 + ½ O2 H2O
C +O2 CO2
C + ½ H2 + 1/2 Cl2 CHCl3
The standard heat of reaction, standard heat of formation, and standard heat of
formation are respectively the heat of reaction, heat of combustion and heat of formation
under 1 atmosphere starting and ending with all materials at constant temperature of
25 0 C.
In chemical industries, processes are carried out under isothermal conditions
and this requires the addition or removal of heat from the reactor. Heat of reaction
values will give the amount of heat to be removed or added. Knowing of this heat
value helps to design the heat exchange equipment.
Standard heat of reaction
Calculation of ∆H 298 form heats of formation data:
The standard heat of reaction accompanying any chemical change is equal to
the algebraic sum of the standard heats of formation of products minus the
algebraic sum of the standard heat of formation of reactants.
∆Hr = ∑∆H f 298 products - ∑∆Hf 298 reactants
Heat of formation of any clement is zero