Equilibria (How far?) Flashcards
What method do you use to find the concentrations of reactants and products at equilibrium for Kc?
The ICE method.
I- Initial moles
C- change in moles
E- equilibrium moles.
Divide equilibrium moles by volume in dm3 to get equilibrium concentration. Then substitute into kc
If the forward reaction is exothermic, how does raising temperature affect the value of kc?
kc decreases because the equilibrium shifts in the endothermic direction to reverse the changes. So more reactants are made. (reactants are the denominator and a large denominator gives a smaller value).
Why is temperature the only factor affecting kc?
Temperature change increases KE, changing concentration of products and reactants.
Catalyst - doesn’t affect concentration.
Pressure - increasing the pressure increases concentration of ALL gases in equilibrium by differing amounts (due to presence of ^powers), changing the ratio. So the equilibrium shifts to minimise the change, restoring product and reactant ration concentration. Kc remains the same.
(AKA: Pressure and concentration change cause equilibrium shift that counteract concentration change. But temperature change causes equilibrium shift that results in concentration change.)
What is Kp?
The pressure equilibrium constant
What are mole fraction and how do you find them?
The fraction of the amount of all the gas of the total. So the moles of each molecule over the total moles at equilibrium. They should all add to 1 and can be written as deccimals.
What is partial pressure and how do you find them?
The fraction of the total pressure due to (caused by?) each molecule. Calculating by multiplying mole fraction by total pressure.
The units can be Kpa, Pa or atm, it just needs to be clear and consitent.
Give the expression of kp.
kp = pCc / pAa x pBb
What state do the reactants and products need to be in to be included in kp?
They need to be gases. Solids and liquids and aqueous solutions are ignored.
What state do the reactants and products need to be in to e included in kc?
They need to be aqueous, gas or liquid. Solids are ignored
What is kp affected by?
Only temperature change.
Describe the steps taken to find kp.
Write the kp expression.
Find the molar fraction of all the species incolved.
Multiple the molar fractions by total pressure to find the partial pressures.
Insert the pp into kp with the relevant powers.
Calculate kp.
How does temperature affect kp?
Kp value is only valid for one temperature as changing it alters equilibrium pressure and therefore kp.
If temperature makes the equilibrium shift to the RIGHT, kp INCREASES.
If temperature makes the equilibrium shift to the LEFT, kp DECREASES.
