15: Chemical Equilibrium
- Last updated
- Jul 19, 2022
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In previous science classes, you may have learned that one way to distinguish chemical changes from physical changes is that physical changes—such as the melting and freezing of water—are reversible, but that chemical changes are not. In this chapter, we will see that this simple answer is not necessarily what it seems.
- 15.2: 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 there is an increase in the number of collisions, an increase in the number of particles that have enough energy to react, and/or an increase in the number of particles with the correct orientation, the rate of reaction will increase.
- 15.3: 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 (they are constant) and there would be no difference in the reaction container. However, reactions are still occurring in both directions.
- 15.4: 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.
- 15.6: Calculating and Using Equilibrium Constants
- An equilibrated system that contains products and reactants in a single phase is a homogeneous equilibrium. A system whose reactants, products, or both are in more than one phase is a heterogeneous equilibrium.
- 15.9: 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.
- 15.10: 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.
- 15.12: The Path of a Reaction and the Effect of a Catalyst
- Adding a catalyst to a reaction 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.
