CHAP. 8: CHEMICAL EQUILIBRIUM [CONTENTS] 245
Example
The equilibrium constant of the reaction
0 =FeO(s) +CO 2 (g)−FeCO 3 (s)
at a temperature of 25◦C isK= 0.000216 (the chosen standard state: pure component at the
temperature and pressure of the system for the solids, and an ideal gas at the temperature of the
system and standard pressurepst= 101.325 kPa for carbon dioxide). At what pressure would
this temperature be the decomposition temperature?
Solution
K=
aCO 2 aFeO
aFeCO 3
=
φCO 2 pCO 2
pst
.
Assuming ideal behaviour of the gas phase, then
pCO 2 =K·pst= 21. 89 Pa.
The temperature 25◦C would be the decomposition temperature of iron (II) carbonate at an
ambient pressure of 21.89 Pa.
