Chemical Equilibrium and Molecular Populations
Dynamic Equilibrium
Forward and Reverse Processes
At equilibrium, forward and reverse reaction rates are equal, so concentrations remain constant though molecules continue to interconvert. Equilibrium is dynamic, not static.
At equilibrium, which statement is correct?
Equilibrium means equal rates, not absence of reaction.
Correct answer: Forward and reverse rates are equal
What does the equilibrium constant compare?
The equilibrium constant summarizes the composition of a system once equilibrium is reached.
Correct answer: the relative amounts of products and reactants at equilibrium
Le Châtelier's Principle
System Response to Stress
A system at equilibrium responds to a stress by shifting in the direction that partially counteracts the stress. Changes in concentration, pressure, and temperature can all alter the equilibrium position.
Typical Stress Responses
Add reactant
- System shifts toward products
- Some reactant is consumed
Increase pressure for gaseous equilibrium
- System shifts to fewer gas moles
- Effect depends on stoichiometry
For a gaseous equilibrium, increasing pressure tends to favor the side with
Higher pressure favors the side with fewer gas molecules, reducing volume.
Correct answer: fewer gas molecules
If temperature is increased for an endothermic forward reaction, which direction does equilibrium shift?
Adding heat favors the endothermic direction.
Correct answer: toward products