3.1.6 Chemical Equilibria Flashcards
What happens to a reversible reaction at equilibrium? (2)
The forward and reverse reactions proceed at equal rates
The concentrations of reactants and products remain constant
What is needed for dynamic equilibrium to occur? (2)
The reaction must be in a closed system
There must be a constant temperature
What is homogeneous equilibrium?
All reactants and products are in the same state (aqueous counts as liquid)
What is Le Chatelier’s principle?
If a factor is changed which affects a system in equilibrium, the position of equilibrium will move in a direction so as to oppose the change
What is the effect of temperature on equilibrium? (2)
Increasing the temperature of the system will shift the equilibrium to favour the endothermic reaction in order to decrease temperature
Decreasing the temperature of the system will shift the equilibrium to favour the exothermic reaction in order to increase temperature.
What can Le Chatelier’s principle be used for?
Predicting effects of changes in temperature, pressure and concentration on the position of equilibrium in homogeneous reactions
What is the effect of pressure on equilibrium? (2)
Increasing the pressure of the system will shift the equilibrium to favour the side with the fewest moles in order to decrease pressure
Decreasing the pressure of the system will shift the equilibrium to favour the side with the most moles in order to increase pressure
What is the effect of adding a catalyst on equilibrium?
Catalysts have no effect on the position of equilibrium; they increase the rate of both reactions, meaning the state of equilibrium is reached faster
What is Kc?
The equilibrium constant
How is concentration represented in an equation?
Square brackets
How is an expression for Kc derived?
Kc = [products]^(no. of moles) / [reactants]^(no. of moles)
How are the units for Kc derived?
Cancel the units of each concentration on the top and bottom of the fraction in order to derive the units for Kc
What will not affect Kc? (2)
Changes in concentration
Addition of a catalyst
What is ICE?
Initial moles
Change in moles
Equilibrium moles
How is ICE used to find the number of moles in an equilibrium mixture? (2)
The change in moles for one mole of product is the negative change in moles for one mole of reactant
The change in moles is multiplied by the number of moles in a correctly balanced equation
