Chapter 19 Flashcards
What happens when the KC value gets larger?
The position of equilibrium lies further to the RHS
How did you show the units?
On a single line
What is a homogeneous equilibrium?
It’s an equilibrium which contains proceed with the same state of phase e.g all gaseous, all liquids all aqueous.
What is a heterogeneous equilibrium?
It’s an equilibrium which contains species that have different states.
Which species can be included in the KC expression for a homogeneous equilibrium?
All species can be included in the expression.
Which species can be included in the KC expression in a heterogeneous equilibrium?
Only the aqueous and gaseous species are included. Solids and pure liquids are omitted as they remain constant.
How do you workout equilibrium quantities and KC?
- Use the equation to work out the equilibrium amounts of all species.
- Convert into concentration using the total volume of the container (the volume should be in dm3)
- Write Kc and sub in values, to calculate
What is KP?
It’s an equilibrium which involves gases it’s an expressed in terms KP equilibrium constant in terms of partial pressures. Concentration and pressure of proportional to another and KP has a direct relationship with KC
What is an mole fraction
Under the same conditions of temperature and pressure the same volume of different gases contains the same number of moles of gas molecules. The mole fraction of the gas is the same as its proportional by volume to total volume of gases in the gas mixture.
How do you workout mole fraction?
N.o of moles of A/ total n.o of moles in a gas mixture
What does the sum of the mole fractions add up to?
1
What is the partial pressure of a gas?
The contribution that the gas makes towards the total pressure of a gas mixture.
What is the sum of partial pressures of each gas equal to?
Total pressure
How do you calculate partial pressure, p(A)?
Mole fraction (A) x total pressure, P
What are suitable units?
kPa, Pa, atm
For Kp which species are included in a heterogeneous equilibrium ?
Only gaseous species
How do you work out KP?
- Find the mole fraction
- Find the partial pressure
- Calculate Kp
Define Le Chatelier’s principle?
When a system in equilibrium is subjected to an external change the system readjust itself to minimise the effect of that change.
What happens when the concentration increases?
The position of equilibrium shifts in the direction that reduces concentration.
What happens to equilibrium when total pressure is increased
The position shifts to the side with fewer gaseous moles.
What happens to equilibrium when the temperature is increased?
Position shifts in the endothermic direction
What happens when a catalyst is added?
The rate at which equilibrium is established increases.
What does it indicate when K=1?
Equilibrium is halfway between reactants and products
What does it indicate when K=100?
Equilibrium is in favour of the products
What does it indicate when K=1x10-2?
Equilibrium is in favour of the reactants
What does K indicate?
Exact position of equilibrium. When in a reversible reaction the reaction proceeds until the concentration of the species gives K when in the KC expression.
What will not change the value of KC/KP?
Changing the concentration, pressure or adding a catalyst.
When will the equilibrium constant change?
If temperature is changed
What happens in an exothermic reaction?
If the forward reaction is exothermic the equilibrium constant decreases with increasing temperature. Raising the temperature decreases the product yield. The position shifts to the left.
THE CONSTANT DECREASES WITH INCREASING TEMPERATURE.
What happens when the ratio is greater than KP?
The partial pressure of the numerator must decrease and the partial pressure of the denominator must increase. Position shift to the left. A new equilibrium will be reached when the KP value is equal to the expression.
What happens in an endothermic reaction?
When the forward reaction is endothermic equilibrium constant increases with increasing temperature. Raising the temperature increases the product yield.
THE CONSTANT INCREASES WITH INCREASING TEMPERATURE.
What happens when the expression is less than KP?
The numerator value must increase and the denominator value must decrease.
What happens if there is an increase in concentration of products?
The numerator will increase. The expression (NOT Kc) will have a value greater than Kc. To restore the expression to Casey the numerator will have to decrease and the denominator will increase. Hence the concentration of reactants increasing and the products concentration decreasing.
What happens when there are fewer moles of gaseous products?
ratio < k
increasing pressure - products increase, reactants decrease
equilibrium shifts to the right
What happens when there are more moles of gaseous products?
ratio > k
increasing pressure - products decrease, reactants increase
equilibrium shifts to the left
What happens when there are same number of gaseous moles?
ratio = k
increasing pressure - no change
no effect to the equilibrium
What happens to the equilibrium constant when a catalyst is added?
Equilibrium constants ARE NOT affected by catalysts.
It affects the rate but not the position, it speeds up the forward and reverse reactions in the equilibrium by the same factor so equilibrium is reached faster.
