Page 463 - Elements of Chemical Reaction Engineering Ebook

434 Steady-State Nonisothermal Reactor Design Chap. 8

8.2.5 Relating AH,,(T), AH;,(T,), and ACp

The heat of reaction at temperature Tis given in terms of the enthalpy of
each species at temperature T, that is,
d b
AH,, (TI = a -H, (T) + a CHc(T) - a -H, (T) - HA (T) (8-14)

where the enthalpy of each species is given by
r
H, = HP(T,) + CPl dT (8- 19)

If we now substitute for the enthalpy of each species, we have

(8-23)

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The first set of terms on the right-hand side of Equation (8-23) is the heat
1
of reaction at the reference temperature TR,

1 AhHg,(TR) = ~H~(T,)+~II~(T,)-$H~(T,)-N;(T,) 24)
(8
-
One can look up The enthalpies of formation of many compounds, Hfo(T,), are usually tabu-
the heats Of lated at 25°C and can readily be found in the Handbook of Chemistry arid
formation at TR,
then calculate the Physzcs' and similar handbooks. For other substances, the heat of combustion
heat of reaction at (also available in these handbooks) can be used to determine the enthalpy of
this formation. The method of calculation is described in these handbooks. From
temperature
these values of the standard heat of formation, Hfo(T,), we can calculate the
heat of reaction at the reference temperature TR from Equation (8-24).
The second term in brackets on the right-hand side of Equation (8-23) is
the overall change in the heat capacity per mole of A reacted, AC,,,
i- I
d C b
CPD -I- -. c - - CPB - CPA (8-25)
a p~ a
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Combining Equations (8-25), (8-24), and (8-23) gives us
I I
Heat of reaction at (8-26)
temperature T

______.
CRC Handbook of Chemistry and Physics (Boca Raton, Fla.: CRC Press, 1996).
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