Equilibrium

Question 1

Definition of a closed system

Answer 1

no exchange of matter with the surroundings

Question 2

Definition of dynamic equilibrium.

Answer 2

rate of forward reaction = rate of reverse reaction

must be in a closed system

Question 3

Draw a graph of rate against time of forward and reverse reactions to equilibrium

Answer 3

See page 2

Question 4

What are features of equilibrium?

Answer 4

macroscopic properties are constant

rate of forward reaction = rate of reverse

closed system

all species in chemical equation will be present in equilibrium mixture

equilibrium can be attained from either direction

Question 5

Definition of Phase Equilibrium.

Answer 5

When the rates of condensation and evaporation are equal

(bromine liquid in vacuum evaporates and condenses constantly)

Question 6

How does increasing temperature affect the position of equilibrium?

Answer 6

favours endothermic direction

(in exam: p.o.e shifts to the …
yield of … increases/decreases)

Question 7

What is Le Chatelier’s principle?

Answer 7

if a system at equilibrium is subjected to some change, the position of equilibrium will shift in order to minimise the effect of the change.

Question 9

How does increasing pressure affect the position of equilibrium?

Answer 9

p.o.e shifts to the side with fewer moles of gas

(in exam: p.o.e shifts to the …
yield of … increases/decreases)

Question 10

What is the effect of increasing the concentration of alkali on equilibrium?

Answer 10

alkali lowers [H⁺] through neutralisation

p.o.e shifts towards acid to replace the removed H⁺

Question 11

How does using a solution affect the equilibrium?

Answer 11

a solution adds H₂O to the mixture

Question 12

What does [A] mean?

Answer 12

concentration of A at equilibrium

Question 13

Concentration =

Answer 13

mol/volume

Question 14

How do you find the equilibrium constant for:
K = A + 2B <–> 3C + 4D

Answer 14

K = ([C]³[D]⁴) / ([A][B]²)

Question 15

When do you use the equilibrium constant?

Answer 15

only for products and reactants in the same physical state

Question 17

How to find how much products there are at equilibrium?

Answer 17

Use RICE:
Ratio
Initial
Change
Equilibrium

Question 18

When do the equilibrium constants change?

Answer 18

With temperature

forward reaction and reverse reaction are different

Question 19

What use is the equilibrium constant?

Answer 19

Tells us how far a reaction proceeds at a particular temperature

Question 20

How does the equilibrium constant differ with temperature?

Answer 20

If K is much bigger than 1, is proceeds almost completely towards the products.

If K is much smaller than 1, it hardly proceeds to the products

If K = 1, position of equilibrium lies in the middle

Question 21

What is the reaction quotient?

Answer 21

ratio of concentrations of the reactants and products at any point in time

Question 22

How to find the reaction quotient, Q?

Answer 22

the same as K

Question 23

How does Q show how far the reaction is towards equilibrium?

Answer 23

If Q<K, reaction must proceed to products to reach equilibrium

If Q>K, reaction must proceed to reactants to reach equilibrium

Question 24

If the reaction vessel is halved in size at constant temperature, what happens to the concentration of each species?

Answer 24

they are doubled

Question 25

What happens to the equilibrium constant as the temperature is raised?

Answer 25

Exothermic reaction:
value of K decreases

Endothermic reaction: value of K increases

Question 26

How to know if a reaction is endothermic or exothermic based on values of K?

Answer 26

if T increases and K decreases:
when K decreases, p.o.e shifts left

when T increases, it favours endo reaction

so reverse reaction is endothermic

Question 27

How do catalysts affect equilibrium?

Answer 27

increase the rate of forward and reverse reaction equally, so reduce time taken to reach equilibrium

doesn’t affect the position of equilibrium

Question 28

What is the difference between K and k?

Answer 28

K – equilibrium constant
shows how far reaction goes towards completion (no information about how quickly reaction occurs)

k – rate constant
how quickly equilibrium is attained (no information about p.o.e and how far reaction proceeds)

Question 29

What does -∆G show?

Answer 29

reaction is spontaneous

Question 30

Draw a graph of gibbs energy on equilibrium?

Answer 30

See page 20

Question 31

What does the equilibrium mixture represent?

Answer 31

the composition that gives the minimum value of the Gibbs energy

Question 32

What does:
∆G = ∆G(^0 with a line through) + RTlnQ

Answer 32

∆G and ∆G(^0 with a line through) in J mol⁻¹ because R is in J K⁻¹ mol⁻¹

∆G(^0 with a line through) – from pure A to pure B (probably given to you)

Q – reaction quotient

R – constant

T – temperature in K

∆G – difference in Gibbs energy between amount of A present in reaction mixture and amount B present.

Question 33

What happens to ∆G as a system moves towards equilibrium?

Answer 33

becomes less negative until it equals zero at equilibrium

Question 34

What happens to ∆G when the system is at equilibrium?

Answer 34

it is 0 – doesn’t move spontaneously in either direction

Question 35

When is the equation:

∆G(^0 with a line through) = -RTlnK

used?

Answer 35

when ∆G = 0

Question 36

What does -∆G(^0 with a line through) show about the p.o.e?

Answer 36

lie closer to products than reactants

[products] > [reactants]
K > 1

Question 37

What does +∆G (^0 with a line through) show about the p.o.e?

Answer 37

lie closer to reactants than products
[products] < [reactants]
K < 1