$16\mathrm{.}5$ ONLy

$16\mathrm{.}5.$ Zinc oxide is reduced by roasting it with carbon in a closed retort in which the gaseous

and liquid products of reaction may be continuously removed. Air is carefully excluded

from the retort so that the reaction is free to proceed under its own equilibrium pressure.

The actual process involves two reactions:

$Zn{O}_{(s)}+C{O}_{(g)}harrZ{n}_{(g)}+C{O}_{2(g)}$

$C_{(s)}+C{O}_{2(g)}$harr$2C{O}_{(g)}$

Zinc produced in the reaction may be removed from the retort as either a gas or a liquid

or both, depending on the operating temperature and pressure.

Data:

She claims that the proper consistency test is

$($a$)$ What does the phase rule indicate about the variance of this system under conditions

where liquid zinc is produced? Under conditions where it is not produced? Explain

carefully.

$($b$)$ Calculate the equilibrium reaction pressure as a function of the roasting

temperature.

$($c$)$ Determine the temperature at which the operation must be conducted in order that

the products may be withdrawn at a pressure of $1\mathrm{.}0$ bar.