# 10: Equilibrium

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• 10.1: The Rate of a Chemical Reaction
The rate, or speed, at which a reaction occurs depends on the frequency of successful collisions. Remember, a successful collision occurs when two reactants collide with enough energy and with the right orientation. That means if we can do things that will increase the number of collisions, increase the number of particles that have enough energy to react and/or increase the number of particles with the correct orientation we will increase the rate of a reaction.
• 10.2: The Idea of Dynamic Chemical Equilibrium
Some reactions are reversible, meaning the reaction can go backwards in which products react to form reactants. If the forward and reverse reactions are happening at the same rate, the reaction is said to be at equilibrium or dynamic equilibrium. At this point, the concentrations of reactants and products are not changing (or are constant) and we would see no difference in our reaction container. However, reactions are still occurring in both directions.
• 10.3: The Equilibrium Constant - A Measure of How Far a Reaction Goes
In the previous section, you learned about reactions that can reach a state of equilibrium, in which the concentration of reactants and products aren't changing. If these amounts are changing, we should be able to make a relationship between the amount of product and reactant when a reaction reaches equilibrium.
• 10.4: Disturbing a Reaction at Equilibrium- Le Châtelier’s Principle
• 10.5: The Effect of a Concentration Change on Equilibrium
• 10.6: The Effect of a Volume Change on Equilibrium
Changing the pressure or volume of a container enclosing an equilibrium system will only affect the reaction if gases are present.
• 10.7: The Effect of Temperature Changes on Equilibrium
When temperature is the stress that affects a system at equilibrium, there are two important consequences: (1) an increase in temperature will favor that reaction direction that absorbs heat (i.e. the endothermic reaction) and (2) the value of Keq will change
• 10.8: The Path of a Reaction and the Effect of a Catalyst
Adding a catalyst to this, or any other equilibrium system, will not affect the position of an equilibrium. A catalyst speeds up both the forward and the reverse reactions, so there is no uneven change in reaction rates. Generally, a catalyst will help a reaction to reach the point of equilibrium sooner, but it will not affect the equilibrium otherwise.

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