Equilibrium (topic 7/17) Flashcards
Le Chatelier’s Principle
When a system in equilibrium is stressed, it moves to oppose the stress. This principle predicts how a reaction/system will respond to one or more changes and what direction the equilibrium will shift.
Kc «_space;1
Equilibrium constant is smaller than smaller than 1, reactants are favoured
Kc»_space; 1
Equilibrium constant is bigger than bigger than 1, products are favoured
What can change Kc?
Only the temperature. Unless you change something in the equation then that would change the equlibrium constant
What can invert Kc?
Reversing the equation
What is Kc?
Equilibrium constant [equilibrium]
What is Q?
Reaction quotient [non-equilibrium]
Bond Breaking
Endothermic
Bond Making
Exothermic
2 conditions for chemical equilbrium to be established for a certain reaction
- Forward and backward reaction occur at the same rate.
- The concentration of reactants and products remain constant.
Can only happen in a closed system, where the reactants and/or products do not come in contact with the surroundings.
Chemical equilibrium at a microscopic level
The reaction does not stop as the reactants are continuously changed to products and the products are continuously changed to the reactants.
Chemical equilibrium at a macroscopic level
There is no change in the properties such as pressure, colour, pH, or concentration.
Physical equilibrium
Does not involve a chemical reaction, rather a change in the state, for example from liquid to gas and gas to liquid.
2 conditions for physical equilbrium to be established for a certain reaction
- The rate of forward process is equal to the rate of backward process.
- The volume of liquid remains constant.
Can only occur in a closed system.
Physical equilibrium at a microscopic level
Where the liquid is getting continuously evaporated and the gas is getting continuously condensed.
Physical equilibrium at a macroscopic level
The properties remain the same, such as color.
The equilbrium constant
Tells us the ratio between concentration of products and the concentration of reactants.
All concentrations have the unit
mol dm^-3
Large value of Kc
Tells us that the concentration of products is much greater than the concentration of reactants at equilibrium, meaning that the forward reaction is favoured and the mixture will contain mostly products.
Small value of Kc
Tells us that the concentration of reactants is much greater than the concentration of products at equilibrium and that the backward reaction is favoured and so the mixture contains mostly reactants.
If the value of Kc = 1
There are equal amounts of reactants and products.
If we take the reverse reaction of Kc
The value of Kc gets reciprocated. Instead of products / reactants, it would be reactants / products.
If Q < Kc
The concentrations of reactants is much greater than the concentration of products, and in order to bring the reaction to equilbrium, the concentration of reactants needs to be decreased.
This means that the forward reaction needs to be favoured in order to bring the reaction back to equilibrium.
If Q > Kc
The concentrations of products is much greater than the concentration of reactants, and in order to bring the reaction to equilbrium, the concentration of products needs to be decreased.
This means that the backward reaction needs to be favoured in order to bring the reaction back to equilibrium.