Impure nickel, refined by smelting sulfide ores in a blast furnace, can be
converted into metal from \(99.90 \%\) to \(99.99 \%\) purity by the Mond process.
The primary reaction involved in the Mond process is
$$
\mathrm{Ni}(s)+4 \mathrm{CO}(g) \rightleftharpoons
\mathrm{Ni}(\mathrm{CO})_{4}(g)
$$
a. Without referring to Appendix 4 , predict the sign of \(\Delta S^{\circ}\)
for the above reaction. Explain.
b. The spontaneity of the above reaction is temperaturedependent. Predict the
sign of \(\Delta S_{\text {surr }}\) for this reaction. Explain.
c. For \(\mathrm{Ni}(\mathrm{CO})_{4}(g), \Delta H_{\mathrm{f}}^{\circ}=-607
\mathrm{~kJ} / \mathrm{mol}\) and \(S^{\circ}=417 \mathrm{~J} / \mathrm{K}\).
mol at \(298 \mathrm{~K}\). Using these values and data in Appendix 4 ,
calculate \(\Delta H^{\circ}\) and \(\Delta S^{\circ}\) for the above reaction.
d. Calculate the temperature at which \(\Delta G^{\circ}=0(K=1)\) for the above
reaction, assuming that \(\Delta H^{\circ}\) and \(\Delta S^{\circ}\) do not
depend on temperature.
e. The first step of the Mond process involves equilibrating impure nickel
with \(\mathrm{CO}(g)\) and \(\mathrm{Ni}(\mathrm{CO})_{4}(g)\) at about
\(50^{\circ} \mathrm{C}\). The purpose of this step is to convert as much nickel
as possible into the gas phase. Calculate the equilibrium constant for the
above reaction at \(50 .{ }^{\circ} \mathrm{C}\).
f. In the second step of the Mond process, the gaseous
\(\mathrm{Ni}(\mathrm{CO})_{4}\) is isolated and heated to \(227^{\circ}
\mathrm{C}\). The purpose of this step is to deposit as much nickel as possible
as pure solid (the reverse of the preceding reaction). Calculate the
equilibrium constant for the preceding reaction at \(227^{\circ} \mathrm{C}\).
g. Why is temperature increased for the second step of the Mond process?
h. The Mond process relies on the volatility of \(\mathrm{Ni}(\mathrm{CO})_{4}\)
for its success. Only pressures and temperatures at which
\(\mathrm{Ni}(\mathrm{CO})_{4}\) is a gas are useful. A recently developed
variation of the Mond process carries out the first step at higher pressures
and a temperature of \(152^{\circ} \mathrm{C}\). Estimate the maximum pressure
of \(\mathrm{Ni}(\mathrm{CO})_{4}(g)\) that can be attained before the gas will
liquefy at \(152^{\circ} \mathrm{C}\). The boiling point for
\(\mathrm{Ni}(\mathrm{CO})_{4}\) is \(42^{\circ} \mathrm{C}\) and the enthalpy of
vaporization is \(29.0 \mathrm{~kJ} / \mathrm{mol}\).
[Hint: The phase change reaction and the corresponding equilibrium expression
are
$$
\mathrm{Ni}(\mathrm{CO})_{4}(l) \rightleftharpoons
\mathrm{Ni}(\mathrm{CO})_{4}(g) \quad K=P_{\mathrm{Ni}(\mathrm{CO})}
$$
\(\mathrm{Ni}(\mathrm{CO})_{4}(g)\) will liquefy when the pressure of
\(\mathrm{Ni}(\mathrm{CO})_{4}\) is greater than the \(K\) value.]
