Equilibrium

Question 1

Characteristics of a dynamic equilibrium

Answer 1

the rate of the forward reaction is equal to the rate of the backwards reaction in a closed system
The concentration of the reactants and products are constant
There is no change in macroscopic properties

Question 2

what is the equilibrium expression

Answer 2

Kc = [A]a [B]b / [C]c [D]d
A&B= concentration of products
a&b= the coefficients of the reactants
C&D= concentration of reactants

Question 3

What does the value of Kc represent

Answer 3

Kc<1 equilibrium favours the reactants
Kc>1 equilibrium favours the products

Question 4

What is not included in the equilibrium expression

Answer 4

NO SOLIDS

Question 5

What affects the value of Kc

Answer 5

temperature, because it can affect the position of the equilibrium
- state thé which position of the equilibrium is favorited and why (endo/exo)

Question 6

If the original equation is doubled or halved what happens to the equilibrium expression

Answer 6

doubled: square the original concentration and their powers
reversed: reciprocal of the original and their powers

Question 7

What is the reaction quotient

Answer 7

the ratio of products and reactants for a reaction that hasn’t reached equilibrium

Question 8

what is the expression for the quotient

Answer 8

concentration of products divided by concentration of reactants

Question 9

The relationship between Q and Kc

Answer 9

Kc = Q the reaction is at equilibrium
Kc > Q then Q will increase and reaction will proceed to the right (more products)
Kc < Q then Q will decrease and reaction will proceed to the left (more reactants)

Question 10

What is the difference between Q and Kc

Answer 10

Kc describes a reaction at equilibrium
Q describes a reaction that is not at equilibrium

Question 11

What affects the position of the equilibrium

Answer 11

• pressure
• temperature
• concentration

Question 12

The effect of temperature on the position of the equilibrium

Answer 12

• increase in temperature will shift the equilibrium to the endothermic side
• decrease in temperature will shift the equilibrium to the exothermic side

Question 13

The effect of pressure on the position of the equilibrium

Answer 13

• increase in pressure will shift the equilibrium to the side with the fewest moles of gas
• decrease in pressure will shift the equilibrium to the side with the most moles of gas

Question 14

The effect of concentration on the position of the equilibrium

Answer 14

• increase in concentration reactants will shift the equilibrium to the right
• decrease in concentration of reactants will shift the equilibrium to the left

Question 15

The effect of a catalyst on the equilibrium

Answer 15

it will speed up the rate of the backwards and forwards reaction and will not affect the position of the equilibrium or Kc

Question 16

Outline the relationship between Kc and temperature

Answer 16

Kc is temperature dependent
- when temp. increases so does the value of Kc

Question 17

What does a high value of Kc mean

Answer 17

there is a higher concentration of products than reactants at equilibrium

Question 18

What does a low value of Kc mean

Answer 18

there is a higher concentration reactants than products at equilibrium

Question 19

What happens to Kc when the reaction is reversed

Answer 19

1/Kc

Question 20

What happens to Kc when adding two reactions together

Answer 20

Kc x Kc

Question 21

What happens to Kc when doubling the reaction

Answer 21

(Kc)^2

Question 22

What happens to Kc when halving the reaction

Answer 22

(Kc)^1/2

Question 23

How to calculate the concentration of reactants and products at equilibrium

Answer 23

use I.C.E method
- if Kc>0: it means it favours the products x will be negative for reactants
- if n° of moles is not stated it is 0
- don’t forget to match the coefficients (2Fe = 2x)

Question 24

Outline the relationship between K and gibbs free energy

Answer 24

Kc>1 = ΔG is negative
Kc =1 = ΔG is 0
Kc<1 = ΔG is positive