Page 124 - Chemical equilibria Volume 4

100 Chemical Equilibria
by equations [3.98a] and [3.98b], is common to all the iso-composition
curves. The position of O depends only on the stoichiometric numbers in the
balance equation.
The equilibrium point E for the system under examination here
(Figure 3.16) is therefore at the intersection of the iso-composition curve – the
straight line Om (with m being fixed by the initial mixture u) and the iso-Q
(I)
curve corresponding to the value of the equilibrium constant K at the
temperature in question. All of this is calculated for a given pressure, because
the diagram is isobaric.

3.6. Quaternary diagrams of chemical equilibria

It is possible to plot diagrams for equilibria involving a polycomponent
phase with four components of the reaction. The system contains three
independent components. These diagrams are square. To demonstrate their
representation and their operation, we shall consider the reduction of carbon
dioxide by hydrogen, in accordance with:
CO 2 + H 2 = CO + H 2O [3R.27]

On the horizontal abscissa axis, we shall show the proportion of carbon in
the CO state, and on the vertical axis, the proportion of H 2 in the state of free
H 2 gas. Hence, we shall have:
{CO }
x = [3.99a]
{CO + 2 }
} {CO
{ }
H
y = 2 [3.99b]
+
{ } {H O }
H
2
2
Because of the conservation of carbon, we can write:
{ } {CO+ 2 } Const. k= = C [3.100]
CO
Similarly, for the conservation of hydrogen:

{ } {H O+ 2 } Const. k= = H [3.101]
H
2