chemical equilibrium

Question 1

What is a closed system?

Answer 1

?
A container in which nothing cannot enter or leave except for heat.

Question 2

What is dynamic equilibrium?

Answer 2

● When the forward and backward reactions are occurring at the same rates.
● Thus, the concentrations stay constant. Yet, the amounts of each may differ.

Question 3

What is Le Chatelier’s Principle

Answer 3

If a dynamic equilibrium is changed, the position of the equilibrium to oppose this change.

Question 4

What happens to the equilibrium posi;on if the temperature is increased and why?

Answer 4

● Favours the endothermic side.
● To minimise the effect of temperature rise by absorbing heat.

Question 5

What happens to the equilibrium posi;on if the temperature is decreased and why?

Answer 5

● Favours the exothermic side.
● To increase the temperature by giving out heat
Low temperatures may give a higher yield of product but will also result in slow rates of reaction. Often a compromise temperature is used that gives a reasonable yield and rate

Question 6

What effect would increasing temperature have on the yield of ammonia?

Answer 6

If temperature is increased the equilibrium will shift to oppose this and move in the endothermic, backwards direction to try to decrease temperature. The position of equilibrium will shift towards the left, giving a lower yield of ammonia.

Question 7

What happens to the equilibrium posi;on if pressure is increased?

Answer 7

● Favous the side producing the least moles of gas (1).
● To minimise the effect of pressure increase by reducing the
number of par6cles.
Remember that each mole takes 24dm3 under standard condi6ons!

Question 8

What happens to the equilibrium posi;on if pressure is decreased?

Answer 8

● Favours the side with more moles of gas (1).
● To minimise the effect of pressure increase by reducing the
number of particles .
If the number of moles of gas is the same on both sides of the equation then changing pressure will have no effect on the position of equilibrium
Increasing pressure may give a higher yield of product and will produce a faster rate. Industrially high pressures are expensive to produce ( high electrical energy costs for pumping the gases to make a high pressure) and the equipment is expensive (to contain the high pressures)

Question 9

What compromises must be made when altering the equilibrium posi;on and why?

Answer 9

Pressure:
• A lower pressure when favouring the side with less moles ∵ high pressures are difficult to produce (high electrical costs in pumping gas) and difficult to contain (to withstand high pressures).
• A higher pressure when favouring side with more moles otherwise the rate of reaction will be too low.
Temperature:
• A higher temperature when favouring the exothermic side otherwise the rate of reaction will be too low.
• A lower temperature when favouring the endothermic side ∵ expensive to use too much fuel.
• Because this allows for a reasonable rate of reaction / costs without shifting the equilibrium too far to the left/right.
• You will have a smaller equilibrium yield but more product produced in unit 6me.

Question 10

What happens to the equilibrium posi;on if a catalyst is added and why?

Answer 10

● No change as it increases the rate of reaction for both sides.
● The time at which equilibrium is achieved is reduced.