3 heat content or enthalpy is a thermodynamic variables and an extensive property . the
increase in enthalpy of a system accompanying a change in the system at constant pressure
equal to the heat absorbed by the system.
=(UB+PVB)-(UA+PVA)
HEAT CAPACITY : the specific heat capacity can be defined as the amount of heat required
to raise the temperature of 1 g of that substance by 1 degree c . the heat capacity the
amount of heat required to raise the temperature of that system by 1 deg c or the rate of
change of heat absorbed by the system with increase in temperature .
Thermochemistry : the study of heat changes in chemical reactions.
Exothermic reaction: the reaction with heat is evolved such as the combustion of aluminum
powder. When the reaction is absorbed heat from external heating is called endothermic
reaction such as commercial extraction of zinc.
Metallurgical processes are usually carried out at constant pressure so that we will consider
the heat evolved by the system at constant pressure qp. there are several types of enthalpy
such as : heat of reaction, heat of solution, heat of transformation, heat of combustion, heat
of formation a compound.