Equilibria chemistry
 

Gaseous equilibria

User Guide

Introducing Kp

[INSERT GE_CI_03_ima]

We've already met the equilibrium constant, Kc, expressed in terms of concentrations. For reactions involving gases, however, it is much more convenient to express the amount of gas present in terms of its partial pressure rather than its concentration. We can write an expression for the equilibrium constant, Kp, in terms of partial pressures.

For the reaction: H2(g) + I2(g)  2HI(g), we can write either: 

\inline \dpi{100} K_{\textup{c}}= \frac{[\textup{HI}]^{2}}{[\textup{H}_{2}][\textup{I}_{2}]}

or

\inline \dpi{100} \small K_{\textup{p}}= \frac{(P_{\textup{HI}_{2}})^{2}}{(P_{\textup{H}_{2}})(P_{\textup{I}_{2}})}

where

\inline \dpi{100} \small P_{\textup{HI} } = partial pressure of HI

\inline \dpi{100} P_{\textup{H}_{2} } = partial pressure of H2

\inline \dpi{100} P_{\textup{I}_{2} } = partial pressure of I2

What would be the Kp expression for the equilibrium 2NH3(g)  N2(g) + 3H2(g)?

  \inline \dpi{100} K_{\textup{p}}= \frac{(P_{\textup{N}_{2}})(P_{\textup{H}_{2}})^{3}}{(P_{\textup{NH}_{3}})^{2}}

What is the equilibrium equation for the system for which \inline \dpi{100} K_{\textup{p}}= \frac{(P_{\textup{NO}_{2}})^{2}}{(P_{\textup{NO}})^{2}(P_{\textup{O}_{2}})}?

2NO(g) + O2(g)  2NO2(g)

 
This is new version