3.1.10 Equilibrium constant Kp for homogeneous systems
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When is Kp used?
During a reversible reaction in the gas phase
Kp [definition]:
The equilibrium constant for an equilibrium reaction involving gases
Total pressure [definition]:
The sum of all the pressures of the individual gasses (sum of partial pressures)
How is the partial pressure of a gas calculated?
By using mole fractions
Mole fraction =
no. of moles of gas/ total moles of gas in mixture
Partial pressure =
mole fraction of gas x total pressure
What are the units for mole fractions and partial pressure?
kPa
Kp [equation]:
(PC)ᶜ (PD)ᵈ / (PA)ᵃ (PB)ᵇ
How does temp affect Kp? [2]:
• Kp is only valid for one temp - Changing temp will change equilibrium pressure so it will change Kp
What happens to Kp when the temperature change causes the equilibrium to shift to the right?
Kp will increase
What happens to Kp when the temperature change causes the equilibrium to shift to the left?
Kp will decrease
What happens when the partial pressure of products increases?
Kp increases
What happens when the partial pressure of products is increased?
Kp drops
How does pressure affect Kp
The value of Kp is UNAFFECTED by pressure changes
What is the effect of a catalyst on Kp? [3]:
• Adding catalyst has no effect on Kp • Catalyst speeds up rate of reaction • so the rate at which equilibrium is established