Modern inorganic chemistry

ENERGETICS 71

Hence for the reduction of zinc oxide by carbon monoxide we have,

ZnO + CO = Zn + CO,

Here K = Kl/K 2. hence Iog 10 K = logi oK} -loglQK

The 'complete' reduction of zinc oxide is favoured by a small value

of K, i.e. when Iog 10 K 2 $> Iog 10 K{. Figure 3.5 shows plots of

Iog 10 KI, and Iog 10 K^ against 1/T; where the two graphs intersect

Iog 10 K for the reduction process is zero and hence K = 1.

At higher temperatures log 10 K has a positive value and K

becomes large. Thus complete reduction of the oxide is energetically

(and indeed kinetically) feasible.

Similar graphs can be plotted for the reduction of any metal

oxide and also for the reduction of chloride and sulphide ores.

FACTORS CONTRIBUTING TO THE ENTHALPY OF
REACTION

In the preceding sections we have considered the overall change in
a chemical reaction. Factors contributing to this change will now be
considered for simple covalent and ionic systems.

COVALENT COMPOUNDS: THE HYDROGEN HALIDES

Let us consider again the reaction between hydrogen and chlorine:

H 2 (g) + Cl 2 (g) -> 2HCl(g)

An energy diagram for this reaction is given below (see Figure 3.6).

(Note that this is not a representation of the actual reaction path

2H(g)+a 2 (q)

H 2 (gH-a 2 (g)

Ah,

Ah 4

2HCl(g)

Ah,