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?
An equilibrium halfway between products and reactants
What does a K value larger than 1 mean?
An equilibrium in favour of the products
What does a K value less than 1 mean?
An equilibrium in favour of the reactants
When will the value of K change?
When the temperature changes
If the forward reaction is exothermic, what happens when you increase the temperature?
The equilibrium constant decreases
The yield of the products decreases
The position of equilibrium shifts to the left
What happens to the equilibrium constant if you change the pressure or concentration?
It doesn’t change
Explain why changing the concentration of one of the species at equilibrium shifts the position of equilibrium
First, work out the initial value of K
Then, work out the new value of K using the given concentrations
If this is less than the original value of K, the numerator must increase and the denominator decreases
This shifts the equilibrium to the right, and vice-versa if the new value of K is more than the original value
How does a catalyst affect the equilibrium constant?
They affect the rate of the reaction but not the position of equilibrium because they increase the forward and reverse reactions by the same rate
Explain why changing the pressure of one of the species at equilibrium changes the position of the equilibrium
First, work out the initial value of Kp
Then, work out the new value of Kp using the given pressures
If this is less than the original value of K, the numerator must increase and the denominator decreases
This shifts the equilibrium to the right, and vice-versa if the new value of Kp is more than the original value
Explain why increasing the temperature of an equilibrium where the forward reaction is endothermic will shift the equilibrium
Increasing the temperature increases the value of Kp
The numerator must increase
The denominator must decrease
The equilibrium shifts towards the products (to the right)
Explain why increasing the temperature of an equilibrium where the forward reaction is exothermic will shift the equilibrium
Increasing the temperature will decrease the value of K
The numerator must decrease
The denominator must increase
The equilibrium shifts towards the reactants (to the left)
