# 25.9: Other Gas Mixtures

- Page ID
- 32769

The oxygen required to cause oxidation in the gas phase need not to come from oxygen gas. Consider the following reaction:

2CO _{(g)} + O_{2} _{(g)} = 2CO_{2} _{(g)}

For this reaction,

\[ K_{ \frac{CO}{CO_2} } = \frac {p^2_{CO_2}} {p^2_{CO} p_{O_2}} \]

or

\[ p_{O_2} = \frac {p^2_{CO_2}} {p^2_{CO}} K_{ \frac{CO}{CO_2}} \]

and hence

\[ ln \frac{1}{p_{O_2}} = ln K_{ \frac{CO}{CO_2} } +2 ln \frac {p_{CO}} {p_{CO_2}} \]

\[ = \frac{-\Delta G}{RT} \]

We see that p_O2 is equivalent to a ratio:

\[ \frac{p_{CO_2}}{p_{CO}} \]

Another nomographic scale may be added to the diagram, with a new origin, C where the CO/CO_{2} line crosses the y-axis.

Similarly for the reaction 2H_{2} + O_{2} = 2H_{2}O; *p*_{O2} is equivalent to

\[ \frac{p_{H_2O}}{p_{H_2}} \]

Adding a further nomographic scale to the diagram, we see that the equilibrium pressure ratios of CO and CO_{2} or H_{2} and H_{2}O for a given oxidation of metal, or reduction of an oxide, can be deduced at a given temperature from the diagram.