Chapter 19 - Equilibrium

Equation for Kc

Kc = [Products] / [Reactants]

How can you compare values of Kc

The larger the value of Kc, the closer the position of equilibrium to the products

Define a homogenous equilibria

Contains species that all have the same state or phase

Define a heterogenous equilibria

Contains species that have different states or phases

How do you write Kc expressions for homogeneous and heterogeneous equilibria

For homogeneous, the expression should contain all of the species

For heterogeneous, since concentration of solids and liquids are essentially constant, they are not included in the equation

How do you find the mole fraction of a substance

Mole fraction = number of moles of substance / total number of moles in gas mixture

How do you find the partial pressure of a gas A in a gas mixture

partial pressure p(A) = mole fraction of A x total pressure P

What is the equation for Kp

Kp = p(products) / p(reactants)

p = partial pressure

Kp only includes gases because only gases have partial pressures, hence, other species must be ignored

What do K=1, K=100 and K=1×10^-2 indicate

K=1 - Equilibrium halfway between reactants and products

K=100 - Equilibrium well in favour of products

K=1×10^-2 - Equilibrium well in favour of the reactants

When does K change

Change in temperature - Only affected by temperature, not pressure, concentration or catalyst

How does temperature affect K

Forward exothermic:

• Equilibrium constant decreases with increasing temperature

• Increase in temperature decreases yield of product, equilibrium shifts left, Kc and Kp decrease

Forward endothermic:

• Equilibrium constant increases with increasing temperature

• Increase in temperature increases yield of product, equilibrium shifts right, Kc and Kp increase

What if you are given Kc values instead of Kp

Explanations for Kp also work for Kc, if given Kc values just use these instead