Page 188 - Modelling in Transport Phenomena A Conceptual Approach

168 CHAPTER 6. STEADY-STATE MACROSCOPIC BALANCES

The standard heat of reaction can be calculated as

(6.3-24)

Substitution of Q. (6.3-23) into Eq. (6.3-24) gives
(6.3-25)

Note that the standard heat of formation of an element is zero.
If heat is evolved in the reaction, the reaction is called exothewnic. If heat is
absorbed, the reaction is called endothermic. Therefore,

> 0 for an endothermic reaction
AHf.,( < 0 for an exothermic reaction (6.3-26)

If the standard heat of reaction is known at 298K, then its value at any other
temperature can be found as follows: The variation of the standard heat of reaction
as a function of temperature under constant pressure is given by

(6.3-27)

The term (dAH,O,,/W), can be expressed as

(6.3-28)

T
AH&,(T) = AH&.,(T = 298 K) + Lg8 ACg dT (6.3-29)