Equilibria - Y12

Question 1

What is an equilibrium mixture?

Answer 1

A mixture in which the proportions of the components remain constant in a closed system
(doesnt mean its half products half reactants)

Question 2

What is dynamic equilibrium

Answer 2

state in a reversible reaction that rate of forward reaction = rate of reverse reaction

**conc of reactants and products remain constant **

Question 3

Conditions for equilibrium

Answer 3

• only reached in closed system
• can be approached from either direction
• its a dynamic process

Question 4

Equilibrium is a dynamic process

Answer 4

reached when rates of opposing processes, are the same,

Question 5

How do you know if equilibrium has been reached?

Answer 5

when macroscopic properites of system dont change with time
eg density, conc, colour, pressure - dont depend on total quanitity of matter

Question 6

⇌

Answer 6

reversible reaction that can reach equilibrium

Question 7

If the prop of products in equilibrium mixture is increased what happens?

Answer 7

• equilibrium moved to right/forward reaction

Question 8

If the prop of reactants in equilibrium mixture is increased what happens?

Answer 8

equilibrium moved to left/backward direction

Question 9

Le Chateliers principle

Answer 9

Ifa system at equilibrium is disturbed, equilibrium moves in the direction that tends to reduce the disturbance

Question 10

What do pressure changes only affect?

Answer 10

reactions involving gases

Question 11

If you increase the pressure, where does equilibrium move to?

Answer 11

to the side with fewer molecules - they exert less pressure

Question 12

If you decrease the pressure, where does equilibrium move to?

Answer 12

side with more molecules

Question 13

If there are an equal no of moles in a reversible reaction and pressure is changed, what happens to equilibrium?

Answer 13

will not change
both sides affected equally

Question 14

If you increase the temp, what happens to equilibrium?

Answer 14

moves in direction that cools system down

Question 15

What do catalysts do to equilibrium?

Answer 15

dont effect position but allow it to be reached more quickly

Question 16

Problems with using high pressure for the haber process

Answer 16

• causes ethene to polymerise
• increases costs of building the plant and the energ costs of running it

Question 17

Problem with using a low temp in the haber process

Answer 17

• reduce reaction rate - affect how quickly equilibrium is reached - but partially compensated for use of catalyst

Question 18

Steam in the Haber process

Answer 18

• too much steam dilutes the catalyst

Question 19

what does the subscript eqm mean?

Answer 19

that the concs have been measured when equilibrium has been reached

Question 20

K꜀

Answer 20

equilibrium constant
its diff for diff reactions

Question 21

For any reaction that reaches an equilibrium we can write the equation in the form

Answer 21

aA + bB + cC ⇌ xX + yY+ zZ

Question 22

K꜀ division formula

Answer 22

product of product conc / product of reactant conc

Question 23

for an endothermic reaction, if the temp decreases
what happens to K꜀
Effect on products + reactants
direction of change of equilibrium

Answer 23

• K꜀ decreases
• products decrease
• reactants increase
• equillibrium moves left

Question 24

for an endothermic reaction, if the temp increases
what happens to K꜀
Effect on products + reactants
direction of change of equilibrium

Answer 24

• K꜀ increase
• products increase
• reactants decrease
• equillibrium moves right

Question 25

for an exothermic reaction, if the temp increases what happens to K꜀ Effect on products + reactants direction of change of equilibrium

Answer 25

* K꜀ decrease * products decrease * reactants increase * equillibrium moves left

Question 26

for an exothermic reaction, if the temp decreases what happens to K꜀ Effect on products + reactants direction of change of equilibrium

Answer 26

* K꜀ increase * products increase * reactants decrease * equillibrium moves right

Question 27

Where does equilibrium move if the K꜀ increases?

Answer 27

to the right

Question 28

Where does equilibrium move if the K꜀ decreases?

Answer 28

to the left

Question 29

what happens to the equilibrium constant for an exothermic reaction when u increase the temp?

Answer 29

decreases

Question 30

what happens to the equilibrium constant for an endothermic reaction when u increase the temp?

Answer 30

increases

Question 31

What is Kc only affected by?

Answer 31

temp changes

Question 32

What does it mean if Kc is greater than 1?

Answer 32

products predominate over reactants and the equilibrium position is over to the right

Question 33

What does it mean if Kc is less than 1?

Answer 33

reactants predominate and the equilibrium position is over to the left

Question 34

What does it mean if the Kc of a reaction is greater than 10¹⁰?

Answer 34

going to completion

Question 35

What does it mean if the Kc is less than 10⁻¹⁰?

Answer 35

not taking place at all

Question 36

Do catalysts affect the value of Kc?

Answer 36

No, so therefore they dont affect the position of equilibrium

Question 37

Why dont catalysts affect the value of Kc?

Answer 37

* they affect the rates of both forward and back reactions equally * by reducing activation energy * so they only affect the rate equilibrium is attained

Question 38

How is the conc expressed for gaseous equilibria?

Answer 38

* using partial pressures rather than conc

Question 39

does exothermic and endothermic cool/heat surroundings?

Answer 39

* exothermic - heats * endothermic - cools

Question 40

Higher pressure - why is it expensive

Answer 40

* strong pressure vessels needed * supplying energy for high pressure is expensive

Question 41

if reactant steam conc increases what happens to equilibrium?

Answer 41

to right to remove increase in steam

Question 41

Why is high temp expensive?

Answer 41

* cost of plant able to resist high temp is too high

Question 42

ICE

Answer 42

Initial, change, equilibrium mixture

Question 43

explain why the amount of S (product) increases when water is added to the equilibrium mixture

Answer 43

* equilibrium shifts to side with most moles * to oppose decrease in conc of all reactants and products

Question 44

how you know a reaction is exothermic (temp and yield)

Answer 44

* higher yield at lower temp * equilibrium has shifted left in the endothermic direction to oppose the increase in temp

Question 45

explain why using a catalyst has no effect on percentage yield

Answer 45

increases rate of forwards and reverse reactions equally

Question 46

one environmental problem chlorodifluromethane can cause but not pentane and why

Answer 46

* ozone depletion * pentane doesnt have c-cl bonds

Question 47

what lang to use when talking about shifts in equilibrium

Answer 47

equilibrium shifts in the endo/exo direction to oppose...

Question 48

brackets for kp

Answer 48

normal brackets + add pp before elements

Question 49

what is kc and kp only affected by

Answer 49

temp

Question 50

pp units

Answer 50

pa or kpa

Question 51

effect of using catalyst on yield

Answer 51

no effect, increases rate of forward and reverse reactions equally

Question 53

Why doesnt the total vol of the mixture need to be measured to allow a correct value for Kc?

Answer 53

equal no of moles on each side of equation

Question 54

6 marker optimum conditions

Answer 54

* talk about optimum temp * how it changes (if graph) * cost * speed - low pressure = too slow

Question 57

why adding more water to equilibrium mixture will lower amount of A in mixture

Answer 57

* conc falls * equilibrium moves to side with more moles * to oppose decrease in conc

Question 58

benefits of using a catalyst, low temp low pressure

Answer 58

* catalyst = no effect on tield * allows lower temp = lowers cost * low pressure = low cost