Chapter 14: Principles of Chemical Equilibrium Flashcards
Reversible reactions
Can proceed in both forward and reverse directions
What becomes constant when at equilibrium?
The concentrations
What becomes equal at equilibrium?
The rates
The equilibrium expression despribes the concentration of reactants and products when the net rate of the reaction is_____?
Zero
Rate Law
Describes how the rate of a reaction changes with concentration
What are the 5 rules of the equilibrium constant?
- Applies only at equilibrium
- Is related to the stoichiometry of the balanced net reaction
- Is independent of initial concentrations
- Is dimensionless and has no units
- Pure solids and liquids are not included because their activities are constant and equal to 1.
How are the forward and reverse Keq related?
Keq forward = 1/Keq reverse
What does a big Keq favour?
Products
What does a small Keq favour?
The reactants
For nonequilibrium conditions, Keq is replaced by?
Q
If Q<Keq?
The reaction shifts to the products
If Q>Keq?
The reactions shifts to the reactants
If Q = Keq?
The reaction is at equilibrium and there is no net change
What is Le Chatelier’s Principle?
When a change is imposed on a system at equilibrium, the system will react in the direction that reduces the change
What does Le Chateliers principle not apply to?
The addition of catalysts. Catalysts change the rate of the reaction, not the equilibrium conditions
Does adding a solid or liquid change the equilibrium concentrations?
No
What is the only variable that can change Keq?
Temperature
An increase in temperature always shifts the equilibrium position in the ______ direction.
Endothermic
A decrease in temperature always shifts the equilibrium position in the __________ direction
Exothermic
What does increasing pressure do to the system?
Shifts to the side of the reaction with fewer number of moles of gas
What does decreasing the pressure do to the system?
Shifts the side of the reaction with the greater number of moles of gas
If there are the same number of gas molecules on both sides of the equilibrium?
Increasing/decreasing the pressure has no effect on the position of the equilibrium
If the equilibrium constant has a very small value, we can assume what?
That the change required to reach equilibrium (x) is very small and can be ignored
What do you do with a very large equilibrium constant?
Work backwards. Start by acting as though the reaction went to completion, then work your way to equilibrium.
What are the two categories for an aqueous solution?
Major species and minor species
What is a major species?
High concentrations
What is a minor species?
Low concentrations
What is the dominant equilibrium?
The more important equilibrium. Always has major species as its reactants, but the products can be major or minor
What species is always a major species in an aqueous solution?
H2O
In aqueous salt solutions, major species are ______ molecules and _______ generated by the salt
Water molecules
Cations and anions
What are the major species of a strong acid?
H2O and H3O+ by removing a proton from the acid
What are the major species in an aqueous solution of a strong base?
H2O, OH-, and the cation generated by the base
What are the three categories for aqueous equilibria?
- Proton Transfer (Acid/Base)
- Solubility (excess solid salt and a saturated solution indicate a solubility equilibrium
- Complexation (When metal cations in aqueous solutions form bonds to anions or neutral molecules that have lone pairs of electrons)
The equilibrium constant for transfer of a proton from an acid to a water molecule is called ________?
The acid hydrolysis constant (Ka)
The equilibrium constant for the transfer of a proton from water to a base is called________?
The base hydrolysis constant (Kb)
The solubility of a solid compound in water is described by the _______?
Solubility product constant (Ksp)
The equilibrium constant for the formation of a complex ion is called______?
The formation constant (Kf)
Spectator ions
Ions that undergo no significant reactions
