L4 - Le Châtelier’s Principle
Effect of a Concentration Change
The first effect that we are going to explore is the change in concentration in a system. When the quantity of a substance changes, the concentration of that substance changes and begins to stress the system. As a result, the system attempts to compensate for the change by shifting the equilibrium of the system based on the new concentrations in the system. The direction of the shift depends on whether the quantity of the substance is increasing or decreasing.
| Increasing concentration | The system shifts away from the side with increasing concentration and the reaction begins to favor the opposite side |
| Decreasing concentration | The system shifts towards from the side with increasing concentration and the reaction begins to favor that side as it "fills the gaps" |
Example 1
|
Using the Haber process of converting nitrogen and hydrogen gas into ammonia, N2(g) + 3 H2(g) ⇌ 2 NH3(g) If the concentration of the nitrogen gas has increased in the system, and using Le Châtelier's principle, we can predict that the forward reaction will be favored. This will result in an increase in the amount of ammonia being produced. Then if the concentration of nitrogen gas decreases, the reaction will favor the reverse reaction and the amount of ammonia will decrease. This is often shown in a condensed format,
|
What is the Haber ProcessIf you want to know more about the Haber process on an industrial scale, please watch the video below before continuing on. |
This format can be extended to include all the substances in the reversible equilibrium equation to determine the effects of altering all the substances.
| Stress | Equilibrium | [N2(g)] | [H2(g)] | [NH3(g)] |
| Adding H2(g) |  |
 |
 |
 |
| Removing H2(g) |  |
|
|
|
| Adding NH3(g) | |
|
|
|
| Removing NH3(g) | |
|
|
|
Notice that the system will always try to re-establish equilibrium no matter what concentration is changed.