CL 10- equilibrium

Question 1

closed system

definition

Answer 1

a system where nothing can get in or out

Question 2

dynamic equilibrium

definition

Answer 2

• the rate of the forwards reaction is equal to the rate of the backwards reaction
• the concentrations of the reactants and products remain constant

Question 3

N₂(g) + 3H₂ (g) ↔ 2NH₃ (l) ∆H = -92kJ mol⁻¹
what effect will increasing the temperature have on the position of equilibrium?

Answer 3

if the temp is increased, the system opposes the change and favours the reverse reaction, which is endothermic, so shifts to the left

Question 4

N₂(g) + 3H₂ (g) ↔ 2NH₃ (l) ∆H = -92kJ mol⁻¹
what effect will increasing the pressure have on the position of equilibrium?

Answer 4

if the pressure is increased, the system opposes the change and favours the side with the fewest amount of moles, so shifts to the right (4 on left, 2 on right)

Question 5

N₂(g) + 3H₂ (g) ↔ 2NH₃ (l) ∆H = -92kJ mol⁻¹
what effect will removing NH₃ have on the position of equilibrium?

Answer 5

if NH₃ is removed, the system opposes the change by making more NH₃, so shifts to the right

Question 6

N₂(g) + 3H₂ (g) ↔ 2NH₃ (l) ∆H = -92kJ mol⁻¹
what effect will adding a catalyst have on the position of equilibrium?

Answer 6

using a catalyst has no effect on the position of equilibrium, because the catalyst speeds up the forward and reverse reactions equally

Question 7

N₂(g) + 3H₂ (g) ↔ 2NH₃ (l) ∆H = -92kJ mol⁻¹
the haber process to make ammonia takes place at about 400 °C and at 150 atm pressure with an iron catalyst.
explain why these conditions are used

Answer 7

explanations of equilibrium positions
* the forwards reaction is exothermic. this means increasing the temperature would favour the reverse reaction, as this is endothermic. to favour the production of ammonia, a low temperature would produce a higher yield.
* there are fewer moles of gas on the right, so an increase in pressure would favour the forwards reaction, and produce a higher yield of ammonia.
* therefore the ideal conditions would be a low temperature and a high pressure
reasons for compromise
* however, a low temperature results in a slow rate, so a compromise must be made with a slightly higher temperature, so a reasonable yield is produced in a suitable time
* a high pressure is expensive to maintain and could result in explosions, so a compromise is made for a reasonable yield at a reasonable cost
* a catalyst is also added to enable lower temperatures to be used and speed up the process

Question 8

Kc expression for haber process

Answer 8

[NH₃]²
———
[N₂][H₂]³

Question 9

what does a high Kc value mean for the position of equilbrium?

Answer 9

shifts to right

Question 10

what does a low Kc value mean for the position of equilbrium?

Answer 10

shifts to left

Question 11

what does a Kc value of 1 mean for the position of equilbrium?

Answer 11

in middle