Equilibrium Flashcards
Key points in a dynamic equilibrium
Rate of forward reaction = rate of back reaction
Concentration of products/reactants don’t change
Must be in a closed system
State Le Chatelier’s Principle
System in equilibrium will counter any external changes to minimize the effect of the change
Position of equilibrium
Indicates extent of reaction and which reaction is favoured
What happens to the P of E when the pressure/conc changes?
P of E changes temporarily
What happens to the P of E when the temperature changes?
P of E changes permanently
Homogenous
All species in same state
Heterogenous
All species in different states
What do you omit in heterogenous equilibria and why
S and L
Not concentrations
What is Kc?
Numerical value of the P of E
Kc<1
P of E closer to reactants
Kc>1
P of E closer to products
Kc=1
P of E is halfway
How to use units
Cross out the same no of mol dm-3 from the top and bottom
Count the no of mols and no of dm-3 and add them
How to calculate equilibrium concentrations
Use given equation and work out equilibrium amounts of all species
Write Kc expression, sub in values and calculate Kc
What is Kp
When equilibria involve gases
Equilibrium constants are in terms of partial pressures
Conc and pressure are proportional, Kc and Kp are related
How to calculate Kp (homogeneous)
Find mole fractions of gases involved
Find partial pressure
Use equation to calculate Kp
How to calculate mole fractions
Gas moles/ total no of gas moles
All mole fraction results should add up to 1
How to calculate partial pressures
Mole fraction/total pressure at equilibrium
How to calculate Kp (heterogenous)
Do the same but omit S and L
What factors affect Kp and Kc
Only a change in temperature affects Kc/Kp
Pressure has no impact on either constant
What happens when the temperature changes
System is no longer in equilibrium
Ratios between reactants and products are no longer Kc/Kp
Partial pressures/concs change to give new values
P of E changes to oppose temperature change
New equilibrium reached, Kc/Kp equal to new value
What happens when the concentration changes
Kc and Kp will initially change but concs/pressures will change back
Catalysts
Decreases time taken for a system to reach equilibrium, increase R of R
Does not affect P of E
