5.1.2 How far? Flashcards
Define Le Chatelier’s principle
If a system at equilibrium is disturbed by a change in conditions, the position of equilibrium moves in the direction that counteracts the change
Define homogeneous equilibria
All species are in the same state
Define heterogeneous equilibria
Species are in different states
How do you write an expression for equilibrium constant?
Kc = [products ( )] ^mole / [reactants ( )] ^mole
What is the unit used in equilibrium constant?
moldm-3
What does a higher Kc mean?
Equilibrium lies to the right
How do you work out Kc using ICE?
Initial amount (mol) - one side starts with moles proportional to each other and the other side starts at 0 mol
Change - add or subtract moles based on moles at equilibrium. should be proportional to moles
Equilibrium amount (mol)
Equilibrium concentration (moldm-3) - calculated using moles/volume.
Use the Kc expression to sub concentrations in
Which factor affects the value of equilibrium constant?
Temperature
How does increasing the temperature affect Kc, assuming the forward reaction is endothermic?
Shifts equilibrium to the endothermic direction to the right towards the products. This increases the yield and therefore the value of Kc
How does decreasing the temperature affect Kc, assuming the forward reaction is endothermic?
Shifts equilibrium to the exothermic direction to the left towards the reactants. This decreases the yield and therefore the value of Kc
Does pressure affect the value of Kc?
No
How do you calculate mole fraction?
Equilibrium moles of one component/ total moles of all components
How do you calculate partial pressure?
Mole fraction of the gas x total pressure of the mixture
What is the sum of the partial pressures?
The total pressure of the mixture of gases
What are the units of pressure?
Pa
How is Kp calculated?
Use the ICE method to find equilibrium moles.
Calculate the mole fraction by dividing equilibrium moles by total moles.
Calculate partial pressure by multiplying mole fraction by total pressure.
Sub into expression for Kp
How do you write an expression for Kp?
Kp = [p products (g)] ^moles / [p reactants (g)] ^moles
What factor affects Kp?
Temperature
How does decreasing the temperature affect Kp, assuming the forward reaction is exothermic?
Kp increases with a decrease in temperature.
Shifts equilibrium in the exothermic direction to the right towards the product.
Yield increases
How does increasing the temperature affect Kp, assuming the forward reaction is exothermic?
Kp decreases with an increase in temperature.
Shifts equilibrium in the endothermic direction to the left towards the reactants.
Yield decreases
Define partial pressure
The pressure due to each gas alone in a mixture
Kp expressions only involve what state of species and why?
Gaseous species because solid species do not have a gas pressure (omitted)
How do catalysts affect equilibrium position?
Remains unchanged. Forward and reverse reaction are affects by the same amount and equilibrium is reached in less time
