Chapter 19 - Equilibrium Flashcards
How do you calculate Kc?
[D]^d x [E]^e
[A]^a x [B] ^b
How do you calculate the units for Kc?
Substitute units into the Kc expression, cancel common units and show the final answer on one line
What are the two types of equilibria?
Homogeneous and heterogeneous equilibria
What is a homogeneous equilibrium?
The equilibrium species all have the same state
What is a heterogeneous equilibrium?
The equilibrium species can be in different states
What is important to remember about calculating Kc for heterogeneous equilibria?
You don’t consider the concentrations of liquids or solids, just gases and those in the aqueous state
What is Kp?
The equilibrium constant in terms of partial pressures
What is the mole fraction of a gas?
The proportion by volume to the total volume of gas in a gaseous mixture
How do you calculate a gas’ mole fraction?
Number of moles of A /
Total number of moles in the gaseous mixture
What will the mole fractions of all the chemicals in equilibrium equal?
1
What is the partial pressure of a gas?
The contribution that a gas makes towards the total pressure
What will the partial pressures of all the chemicals in equilibrium equal?
The total pressure
How do you calculate partial pressure?
Mole fraction of A x total pressure
What species can be substituted into the Kp expression?
Gases only
How do you calculate Kp?
p(C)^c x p(D)^d /
p(A)^a x p(B)^b
What are suitable units for Kp?
Kilopascals (kPa) or atmospheres (atm)
What does a K value of 1 mean?
Equilibrium is halfway between reactants and products
What does a K value larger than 1 mean?
Equilibrium well in favour of products
What does a K value less than 1 mean?
Equilibriums well in favour of reactants
When will the value of K change?
If the temperature is changed
If the forward reaction is exothermic, what happens when you increase the temperature?
Equilibrium will shift to the left and K will decrease
What happens to the equilibrium constant if you change the pressure or concentration?
Nothing
If the forward reaction is endothermic, what happens when you increase the temperature?
Equilibrium shifts to the right and K increases
Explain why changing the concentration of one of the species at equilibrium shifts the position of equilibrium
You can use the le chateliers principle to predict shift as the Kc controls the relative concentrations of reactants and products present at equilibrium.
How does a catalyst affect the equilibrium constant?
Has no effect on the position but the actual rate of the chemical reaction
Explain why changing the pressure of one of the species at equilibrium changes the position of the equilibrium
If fewer moles of gaseous products the ratio < K (products to reactants) is increasing pressure, increases products whilst decreasing the reactants shifting the equilibrium to the right.
Explain why increasing the temperature of an equilibrium where the forward reaction is endothermic will shift the equilibrium
F
