C19 - Equilibrium Flashcards
What’s homogeneous equilibria?
When the equilibrium species all have the same state or phase.
The Kc expression contains concentrations of all species.
What’s heterogeneous equilibria?
When the equilibrium species have different states or phases.
The concentration of solids and liquids are constant so any species which are solid or liquid are omitted from the Kc expression.
What’s the mole fraction of a gas?
How is it calculated?
It’s the same as its proportion by volume to the total volume of gases in a gas mixture.
Mole fraction x (A) = no’ moles of A / total no’ moles in gas mixture
What is the partial pressure of a gas (in a gas mixture)?
The contribution that the gas makes towards the total pressure P.
The sum of the partial pressures of each gas equals the total pressure.
For gas A:
Partial pressure p(A) = mole fraction A * total pressure p
p(A) = x(A) * P
Only gases can have partial pressures.
What does the size of the equilibrium constant K indicate?
K = 1 suggests an equilibrium halfway between reactants and products
K = 100 indicates an equilibrium well in favour of the products
K = 0.01 shows an equilibrium well in favour of the reactants
What causes the equilibrium constant K (c or p) to change?
A change in temperature only, NOT concentration, pressure or a catalyst.
How does the equilibrium constant K change in an exothermic reaction?
K decreases with increasing temperature so the equilibrium yield of products decreases.
Why does the equilibrium constant K (p or c) change in an exothermic reaction if temperature is increased?
Kp (constant using partial pressures) decreases shifting the eq position the the left so the system is no longer in equilibrium.
The ratio of products / reactants is now greater than Kp.
The partial pressure of the products must decrease.
The partial pressure of the reactants must increase.
This position of equilibrium shifts to the left.
A new equilibrium will be reached where the ratio of products / reactants is equal to the new Kp value.
How does the equilibrium constant K (p or c) change in an endothermic reaction if temperature is increased?
The equilibrium constant increases with increasing temperature, increasing the equilibrium yield of products.
If temperature increases, Kp increases and the system is no longer in equilibrium. The ratio of products/reactants is now less than Kp.
The partial pressure of the products must increase.
The partial pressure of the reactants must decrease.
The position of equilibrium shifts towards the products.
How do concentration and pressure affect the equilibrium constants?
They don’t.
Only temperature does.
How is Kc calculated?
Kc = [products] / [reactants]
How is Kp calculated?
Kp = p(products) / p(reactants)
How does an exothermic reaction affect Kp if temperature is increased?
Kp decreases with increasing temperature.
Equilibrium shifts to the left.
How does an endothermic reaction affect Kp if temperature is increased?
Kp increases with increasing temperature.
Kp shifts to the right.
