Chapter 19 - Equilibrium Flashcards
What does a larger Kc value mean ?
The further the position of equilibrium is towards the products
What does a smaller Kc value mean ?
The further the position of equilibrium is towards the reactants
What do the units of Kc depend upon ?
They depend upon the number of concentration terms that are in the equilibrium constant term
How do you work out the units of Kc ?
- Substitute units into the expression for Kc
- Cancel common units and show the final units on a single line
What are the two main types of equilibria ?
Homogenous and heterogenous
What does a homogenous equilibrium contain ?
It contains equilibrium species that all have the same state or phase
What does a heterogenous equilibrium contain ?
A heterogenous equilibrium contains equilibrium species that have different states or phases
What concentrations does a homogenous equilibria contain ?
It contains concentrations of all species
What concentrations does a heterogenous equilibria contain ?
- Any species that are in solid and liquid state are omitted from the Kc expression
- They are automatically incorporated within the overall equilibrium constant
What states do the species have to be for them to be in the Kc expression ?
g or aq
What is a mole fraction ?
The proportion of the volume of a gas to the total volume of gases in the mixture
How do you work out the mole fraction ?
Mole fraction χ(A) = number of moles of A / total number of moles in the gas mixture
What does the sum of the mole fractions equal to ?
Should equal to 1
What does p stand for ?
The partial pressure of a gas
What does P stand for ?
The total pressure
What is the partial pressure ?
The contribution that the gas makes towards the total pressure
How do you work out the partial pressure ?
- p(A) = Mole fraction of A x total pressure P
- p(A) = x(A) x P
What does the sum of the partial pressures equal ?
It equals the total pressure
What state does Kp only include ?
Only includes gases because only gases have partial pressures
With the equilibrium H(2) + I(2) -> 2HI, what is the expression for Kp?
Kp = p(HI)^2 / p(H(2)) x p(I(2))
What does the magnitude of an equilibrium constant represent?
The extent of an equilibrium
Where does the equilibrium position shift if the concentration of a species increases ?
Shifts in the direction that decreases the concentration
Where does the equilibrium position shift if the pressure is increased ?
Shifts towards the side with fewer gaseous moles
Where does the equilibrium position shift if the temperature increases ?
Position shifts in the endothermic direction
What does K = 1 indicate ?
Equilibrium halfway between reactants and products
What does K = 100 indicate ?
Equilibrium well in favour of the products
What does K = 1x10^-2 indicate ?
Equilibrium well in favour of the reactants
What is K at a set temperature ?
Constant and does not change despite any modifications in conc, pressure or the presence of a catalyst
What is the only condition that will cause K to change ?
Temperature
What is the effect on K when the temperature is increased and the forward reaction is exothermic?
- Equilibrium constant decreases
- Equilibrium shifts to the left
What is the effect on K when the temperature is increased and the forward reaction is endothermic?
- Equilibrium constant increases
- Equilibrium shifts to the right
What effect does increasing pressure have on a reaction with fewer moles of gaseous products than reactants?
- Products increase
- Reactants decrease
- Equilibrium shifts to the right
What effect does increasing pressure have on a reaction with more moles of gaseous products than reactants?
- Products decrease
- Reactants increase
- Equilibrium shifts to the left
What effect does increasing pressure have on a reaction with the same number of moles of gaseous products and reactants?
- No change
- Equilibrium stays the same
What is the effect of a catalyst on the equilibrium constant?
- Catalyst affects the rate but not the equilibrium
- Equilibrium is reached faster but position does not change
