Le Chatelier's Principle

Learning Goals

Upon finishing this section you will be able to predict what will happen to the extent of a reaction when the reaction is perturbed by changing the temperature, changing the pressure, or changing the concentration of a reactant or product.


The guiding principle for these three possible perturbations is Le Chatelier's principle which states that "a change in any of the factors that determine the equilibrium conditions of a system will cause the system to change in such a manner as to reduce or counteract the effect of the change." Remember that K is only a function of temperature, so of these three changes only a temperature change will change K. So let's look at the possible ways in which the extent of the reaction can be shifted.

We can now use these conclusions to predict the direction of the shift in equilibrium of a reaction caused by any of these changes.

Review Questions

  1. For the reaction H2(g) + I2(g) --> 2 HI(g), the H298.15 of the forward reaction is 26.36 kJ/mol. For the following changes, predict the direction of the equilibrium shift:
  2. Work Exercise 16.12 on page 776.

Section 16.7 Is There Life After Equilibrium?

Learning Goals

You should understand that not all reactions have their maximum usefulness to us after they attain the equilibrium state.


There are many nonequilibrium reactions that are of extreme importance to us. Such reactions include the chemical reactions occurring in a car battery, the biochemical reactions in plants and animals, the production of elements in stars, etc. The topic of nonequilibrium thermodynamics is extremely important in trying to understand the life process, and the topic is very complicated. Although we cannot embark on a discussion of such topics at this level, it is important to know that nonequilibrium processes exist all around (and in) us, and that they are extremely important to the functioning of our universe.


Web Author: Dr. Leon L. Combs
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