Page 121 - Chemical equilibria Volume 4

Molecular Chemical Equilibria 97
A change from X into –X does not alter y. Therefore, the straight line
MA 3 is the axis of symmetry of the different curves.
1
– Second case: β = β = and β = (case of reduction of CO 2 by
2
0
1
3
2
carbon in the presence of nitrogen)
Equation [3.77] becomes:
2y 2 = K
(I)
x 3 − y
From this equation, we draw x, which gives us:
1 ⎛ 2y + K y ⎞ (I)
2
x = ⎜ ⎟
3 ⎝ K (I) ⎠

The curves are parabolas (Figure 3.15(b)), with their axis parallel to
A 2A 1, and a peak with a the coordinates ( x =− K (I) /3 , y =− 2K ). These
(I)
coordinates are in the ratio 2/ 3. The space of the peaks is therefore the
negative part of the line Δ passing through the origin, with the slope 2/ 3
(Figure 3.15(b)).

– Third case: β = β = 4 and β = (reduction of Fe 3O 4 into metal iron
0
3
1
2
by hydrogen in the presence of nitrogen)
Equation [3.77] becomes:
⎛ 2y ⎞ 4 (I)
⎜ ⎟ = K
⎝ x 3 − y ⎠

We deduce the equation for the curves:
x 3 1/4
y = ( K (I) )
+
2 K 1/4
r
These curves are straight lines issuing from A 2.

The relative positions of the equilibrium curves depend on the sign of the
enthalpy of the reaction. If, for instance, the reaction enthalpy is positive (i.e.