equilibrium (Alevel) Flashcards
how do you find units of kc
sub moldm-3 into expression
what is homogenous equilibrium
contains equilibrium species that all have the same state or phase
what is heterogenous equilibrium
contains equilibrium species that have different states or phases
what is a rule you must remember about kc
concentrations of solids and liquids are essentially constant so are ommitted from the kc expression only aq or g are included
What is the method to calculate kp
1) calculate equilibrium moles
2) change equilibrium moles into mole fractions
3) calculate partial pressures for the gases
4) substitute partial pressure values in
How do you calculate mole fractions
Mol / total moles
How do you calculate partial pressure
Mol fraction x total pressure
What is the mol fraction of a gas
The same as it’s proportion by volume to the total volume of gases in a gas mixture
What is partial pressure
The contribution that the gas makes towards the total pressure . The sum of the partial pressures of each has equals the total pressure
What brackets do we use for kp
Round brackets
What is super important with equilibrium and pressure
Make sure when counting moles on each side you only count the moles of GAS and not a sneaky moles of SOLID
What happens to K at different conditions
At a set temperature k is constant and does not change with concentration, pressure or the prescence of a catalyst. Only temperature will change K . This goes for both Kc and kp
when k>1 what can we say about the position of equilibrium
the position of equilibrium lies to the right because the products concentration is greater
when k<1 what can we say about the position of equilibrium
lies to the left as the value of the reactants is larger
if k=1 what can we say about the position of equilibrium
in the middle as concentrations are the same
why does concentration not effect the value of K
as you increase concentration of reactants equilibrium is reastablished as equilibrium will shift right to product more product as reactant concentration decreases . concentration does not change Kc , this isnt possible for temperature as it has outer temp which changes concentrations
When should you say concentration vs partial pressure
Use partial pressure for kp and concentration for kc
How is kp kept constant when pressure changes
Kp temporarily changes but equilibrium shifts to combat this
Does a catalyst effect k
No it only effects the rate of reaction and does not effect equilibrium . Equilibrium is reached faster but the position is not changed
what do you need to do when writing an ionic equation
- make sure atoms are balanced
-make sure charges on both sides add to zero
what units can kp be in
Kpa , pa or atm
why do we measure pressure instead of concentration for gases
it is easier to measure pressure than concentration , kc has a direct relationship to kp
