Equilibrium

Question 1

what is the symbol for reversible reaction?

Answer 1

⇌

Question 2

what is required for an equilibria to occur?

Answer 2

a closed system where products cannot escape

Question 3

what happens in an equilibria?

Answer 3

forward and reverse reactions occur at the same time and in the same place

Question 4

what happens when the rates of the forwards and reverse reactions are equal?

Answer 4

equilibrium is reached

Question 5

does the amount of products equal the amount of reactants in equilibrium?

Answer 5

no

Question 6

is the rate of the forwards reaction the same as the reverse reaction?

Answer 6

yes

Question 7

do the amounts of products and reactants change in an equilibrium?

Answer 7

no

Question 8

what does a dynamic reaction mean?

Answer 8

• reactants are continuously making products and vice versa, but as this is happening at the same rate, nothing appears to be happening

Question 9

is the position of the equilibrium lies to the LEFT, are there more products or reactants?

Answer 9

reactants

Question 10

is the position of the equilibrium lies to the RIGHT, are there more products or reactants?

Answer 10

products

Question 11

What is Le Chatelier’s principle?

Answer 11

When a constraint is applied to a reversible reaction, the equilibrium will move to oppose the constraint (change)

Question 12

if the forwards reaction is exothermic, then what will the reverse reaction be?

Answer 12

endothermic

Question 13

if the forwards reaction is endothermic, then what will the reverse reaction be?

Answer 13

exothermic

Question 14

what happens to an equilibria when pressure increases?

Answer 14

• it moves to oppose the constraint
• by moving the equilibrium to the side which produces less particles
• as less particles means less collisions with container, reducing pressure

Question 15

what happens to an equilibria when pressure decreases?

Answer 15

• it moves to oppose the constraint
• by moving the equilibrium to the side which produces more particles
• as more particles means more collisions with container, increasing pressure

Question 16

what happens to an equilibria when temperature increases?

Answer 16

• it moves to oppose the constraint
• by moving the equilibrium to the side which is endothermic
• meaning more energy is taken in/absorbed in reaction
• thereby reducing temperature

Question 17

what happens to an equilibria when temperature decreases?

Answer 17

• it moves to oppose the constraint
• by moving the equilibrium to the side which is exothermic
• meaning more energy is released in reaction
• thereby increasing temperature

Question 18

what is ammonia (NH₃) used for?

Answer 18

• fertilisers
• explosives
• dyes

Question 19

how is ammonia manufactured?

Answer 19

the Haber process

Question 20

describe the Haber process?

Answer 20

• N² and H² are passed over iron powder at a moderate temp of 450°C and moderate pressure (200atm) to form ammonia. (only small amount of ammonia actually produced)
• gases go into condensing space where temperatures are kept low so ammonia condenses at -33°C, but H² and N² stay gaseous, and ammonia can be extracted

Question 21

what happens to the unreacted H² and N² from the Haber process?

Answer 21

they are put back into the reaction chamber to react

Question 22

where are N² and H² sourced from?

Answer 22

• N² from air
• H² from reaction of steam and methane

Question 23

what is the equation for the reaction of the Haber process?

Answer 23

3H² (g) + N² (g) ⇌ 2NH₃ (g)

Question 24

ΔH value for the Haber process?

Answer 24

ΔH = -92kJmol⁻¹

Question 25

what would the ideal temperature be for the Haber process and why is that not used?

Answer 25

- ideally want a low temperature so the equilibrium is to the right and more NH³ is produced, but low temperatures means a slow rate of reaction due to few molecules exceeding activation energy and this is inefficient, so a compromise of 450degrees is reached.

Question 26

what would the ideal pressure be for the Haber process and why is that not used?

Answer 26

- ideally a high pressure so equilibrium is to the right and more NH³ produced, but this is costly to maintain, and can cause safety issues, so a compromise of 200atm is reached