equilibrium (Alevel)

Question 1

how do you find units of kc

Answer 1

sub moldm-3 into expression

Question 2

what is homogenous equilibrium

Answer 2

contains equilibrium species that all have the same state or phase

Question 3

what is heterogenous equilibrium

Answer 3

contains equilibrium species that have different states or phases

Question 4

what is a rule you must remember about kc

Answer 4

concentrations of solids and liquids are essentially constant so are ommitted from the kc expression only aq or g are included

Question 5

What is the method to calculate kp

Answer 5

1) calculate equilibrium moles
2) change equilibrium moles into mole fractions
3) calculate partial pressures for the gases
4) substitute partial pressure values in

Question 6

How do you calculate mole fractions

Answer 6

Mol / total moles

Question 7

How do you calculate partial pressure

Answer 7

Mol fraction x total pressure

Question 8

What is the mol fraction of a gas

Answer 8

The same as it’s proportion by volume to the total volume of gases in a gas mixture

Question 9

What is partial pressure

Answer 9

The contribution that the gas makes towards the total pressure . The sum of the partial pressures of each has equals the total pressure

Question 10

What brackets do we use for kp

Answer 10

Round brackets

Question 11

What is super important with equilibrium and pressure

Answer 11

Make sure when counting moles on each side you only count the moles of GAS and not a sneaky moles of SOLID

Question 12

What happens to K at different conditions

Answer 12

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

Question 13

when k>1 what can we say about the position of equilibrium

Answer 13

the position of equilibrium lies to the right because the products concentration is greater

Question 14

when k<1 what can we say about the position of equilibrium

Answer 14

lies to the left as the value of the reactants is larger

Question 15

if k=1 what can we say about the position of equilibrium

Answer 15

in the middle as concentrations are the same

Question 16

why does concentration not effect the value of K

Answer 16

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

Question 17

When should you say concentration vs partial pressure

Answer 17

Use partial pressure for kp and concentration for kc

Question 18

How is kp kept constant when pressure changes

Answer 18

Kp temporarily changes but equilibrium shifts to combat this

Question 19

Does a catalyst effect k

Answer 19

No it only effects the rate of reaction and does not effect equilibrium . Equilibrium is reached faster but the position is not changed

Question 20

what do you need to do when writing an ionic equation

Answer 20

• make sure atoms are balanced
  -make sure charges on both sides add to zero

Question 21

what units can kp be in

Answer 21

Kpa , pa or atm

Question 22

why do we measure pressure instead of concentration for gases

Answer 22

it is easier to measure pressure than concentration , kc has a direct relationship to kp