Lecture 16 : Equilibrium II
Vocabulary:
-Coefficient Rule: When coefficients are changed by a factor of n, Keq to the power of n.
-Reciprocal Rule: When a reaction is revered, the new Keq value is the inverse of the old
Keq value.
-Multiple Equilibria Rule: When two or more reactions are combined, the new Keq is the
product of the Keq values from the individual reactions.
Explanation:
-There are three ways in which Keq can be manipulated:
1.) Coefficient Rule
2.) Reciprocal Rule
3.) Multiple Equilibria Rule
-What the Reaction Quotient (Q) tell you:
Q > Keq : The reaction will proceed to the left. (The reaction will continue to
increase the concentration of the reactants until equilibrium is established.)
Q < Keq : The reaction will proceed to the right. (The reaction will continue to
increase the concentration of products until equilibrium is established.)
Q = Keq : The system is at equilibrium.
-Le Chatelier’s Principle: When the system at equilibrium is subjected to a stress, the
equilibrium will shift in order to reduce that stress. The only three stresses are changes in:
1.) Pressure: does not change equilibrium constant
2.) Concentration: does not change equilibrium constant
3.) Temperature: does change equilibrium constant, volume increases or decreases
-Stress form Increase of Pressure: If the pressure on a system at equilibrium ins
increased, the equilibrium will shift towards the side with the fewer moles of gas to
reduce that stress
Pressure increases  Volume decreases = Produces more
Pressure decreases  Volume increases = Produces less
**This changes the equilibrium concentration, but it does not change the Equilibrium
Concentration (Keq)
-Stress from Decreasing Pressure: If the pressure on a system at equilibrium is
decreased, the equilibrium will shift toward the side with more moles of gas to reduce
that stress.
**The changes the equilibrium concentrations, but it dose not change the Equilibrium
Constant (Keq)
-Stress from Increasing Concentration: If the concentrations of one of the species in an
equilibrium system is increased, the equilibrium will shift in the direction that will reduce
the concentration of that species.
Concentration increase = away
Concentration decrease = to
**This increases the equilibrium concentrations, but it does not change the Equilibrium
Constant (Keq)
-Stress from Decreasing Concentrations: If the concentrations of one of the species in an
equilibrium system is decreased, the equilibrium will shift in the direction that will
increase the concentration of that species.
**This decreases the equilibrium concentrations, but it does not change the Equilibrium
Constant (Keq)
-Stress from Changing Temperature: This is the only stress that changes the equilibrium
constant (Keq)
Temperature Heat: -Exothermic (negative) energy is on the product
- Endothermic (positive) energy is on the reactant
Pictures:
*This is a perfect example of equilibrium*
*Example of adding stress by increasing and decrease pressure*