2.4 Chemical Equilibria Flashcards
What are the requirements of Equilibrium?
- Closed system
- A constant temperature and pressure
- Reversible reaction
- Rates of opposing changes are equal
Properties of Equilibrium
- Dynamic
- Independent of starting point
- Mixed composition
What does the reaction quotient, Q, do?
It relates the amounts of reactants and products to each other at any point of the reaction
What is Qc?
Reaction quotient in concentration
What is Qp?
Reaction quotient in partial pressure
Kpa, atm
What is the Equilibrium Constant, K?
Value of the reaction quotient (Q) at Equilibrium
What do you exclude in Equilibrium expressions?
Solids and Solvents
Substances which DONT have a significant change in concentration
What is the name for everything in a Equilibrium expression being in the same pysical state
Homogeneous Equilibrium
What determines whether to use Kc or Kp?
The units
If concentration units, eg. Mol, use Kc
If pressure units, eg. atm, use Kp
What is a Heterogeneous equilibria?
Involves things in different physical states
Remember, solids and solvents are excluded
What is excluded particularly in Kp expressions
Anything that doesn’t produce pressure
Eg. H2O (l)
Status of a reaction when Q and K are the same?
Equilibrium
What is the status of a reaction when Q is smaller than K?
Bottom of expression is larger, more reactants
Reaction will go towards the products >
What is the status of a reaction when Q is bigger than K?
Top of expression is bigger, more products
Reaction will go towards the reactants <
What does a small values of K show?
Equilibrium lies to the LHS
Reaction stops progressing when there are a large amount of reactants left.
What does a large value of K show?
Equilibrium lies to RHS
Forward reaction continues until theres mostly products and little reactants left
Equation relating Gibbs to the equilibrium position
ΔG = -RTln(Kc)
Small K value in gibbs
Small K gives negative value of ln(kc)
This multipled to -RT, give positive value
Reaction is NOT spontaneous
Large K in gibbs
Large K gives positive value of ln(kc)
This multipled to -RT, give negative value
Reaction IS spontaneous
What is Le Chateliers Principle?
When a change is applied to a system in dynamic equilibrium, the system reacts to oppose the change
What is an isotonic solution?
Osmotic equilibria
Which equilibria does increasing pressure does not affect?
Those that do not involve gases
What effect do catalysts have on equilibrium reactions?
Do not affect K or the position of equilibrium, just get to it faster
Effects of temperature on exothermic reactions
Increasing favours REVERSE
Decreasing favours FORWARD
(think surroundings)
Effects of temperature on Endothermic reactions
Increasing favours FORWARD
Decreasing favours REVERSE
(think surroundings)
