Equilibria chemistry
 

Other equilibrium changes

User Guide

Kp and delta H

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The experiment with the cobalt complexes showed that changing the temperature changes the positon of equilibrium, which means that Kc must change as well. Because Kc and Kp are directly related, changing the temperature must also change the value of Kp. We will look at some data about other equilibrium systems to find out how the value of Kp is related to the enthalpy change of reaction, ΔH.

Remember \inline \dpi{100} \mathit{K}_\textup{p} = \frac{\textup{partial pressure of products}}{\textup{partial pressure of reactants}}

(all data taken from Nuffield Advanced Science Book of Data, Sixth Impression 1980)

N2O4(g)  2NO2(g): ΔH = 58.0 kJ mol–1

Temperature/K 298 400 500 600
K p/atm 1.15 x 10–1 4.79 x 101 1.70 x 103 1.78 x 104

N2(g) + 3H2(g)  2NH3(g): ΔH = –92.4 kJ mol–1

Temperature/K 298 400 500 600
K p/atm–2 6.76 x 105 4.07 x 101 3.55 x 10–2 1.66 x 10–3

H2(g) + CO2(g)  H2O(g) + CO2(g): ΔH = 41.2 kJ mol–1

Temperature/K 298 500 700 800
K p 1.00 x 10–5 7.76 x 10–3 1.23 x 10–1 2.88 x 10–1

2SO2(g) + O2(g)  2SO2(g): ΔHʅ = –19.7 kJ mol–1

Temperature/K 298 500 700 1100
K p/atm–1 4.0 x 1024 2.5 x 1010 3.0 x 104 1.3 x 10–1

How does the value of Kp change when the temperature is increased in an exothermic reaction?

K p decreases as temperature is increased.

How does the value of Kp change when the temperature is changed in an endothermic reaction?

K p increases as temperature is increased.

 
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