Equilibria (CDS)

Question 1

What is a reversible reaction?

Answer 1

A chemical reaction where the products can react to reform the original reactants. It is represented by the double arrow ⇌.

Question 2

What is meant by equilibrium?

Answer 2

A state where a system is in a balanced state with no net change occurring in the rates of the forwards and backwards reaction, or the concentrations of reactants or products

Question 3

What is a closed system?

Answer 3

One where no substances can enter or leave, but energy can be transferred in or out.

Question 4

Features of a system in dynamic equilibrium (4)

Answer 4

1. Both reactions taking place simultaneously
2. In a closed system
3. Forwards and backwards reactions take place at equal rates
4. Reactants and products remain at constant concentration

Question 5

State Le Chatelier’s Principle

Answer 5

If the conditions of a system at equilibrium are disturbed, the position of equilibrium moves in a direction to reduce the disturbance.

Question 6

Increasing the Concentration of a system in dynamic equilibrium

Answer 6

If you increase the concentration of a reactant, the position of equilibrium will shift in a direction to oppose the increase by making more of the product that will remove it.

Question 7

Decreasing the Concentration of a system in dynamic equilibrium

Answer 7

If you decrease the concentration of a reactant, the position of equilibrium will shift in a direction to oppose the increase by making more of the substance that is being removed.

Question 8

In this reaction:
A + B ⇌ C + D
Which direction will equilibrium shift if you increase the concentration of A and why?

Answer 8

Left, in order to make more C + D and remove the additional A that was added

Question 9

In this reaction:
A + B ⇌ C + D
Which direction will equilibrium shift if you decrease the concentration of A and why?

Answer 9

Right, in order to make more A to replace the A that is being removed

Question 10

Increasing the pressure of a system at dynamic equilibrium

Answer 10

If the pressure is increased, the position of equilibrium will move to oppose that change by moving to the side with fewer gas molecules, which will exert less pressure

Question 11

Decreasing the pressure of a system at dynamic equilibrium

Answer 11

If the pressure is decreased, the position of equilibrium will move to oppose that change by moving to the side with more gas molecules, which will exert more pressure

Question 12

In this reaction:
N2O4 (g) ⇌ 2NO2 (g)
Which direction will equilibrium shift if you increase the pressure and why?

Answer 12

Left, because there is only 1 gas molecule on that side

Question 13

In this reaction:
N2O4 (g) ⇌ 2NO2 (g)
Which direction will equilibrium shift if you decrease the pressure and why?

Answer 13

Right, because there are 2 gas molecules

Question 14

In this reaction:
H2(g) + I2(g) ⇌ 2HI (g)
What will happen to the position of equilibrium if you increase the pressure and why?

Answer 14

It will not change because there are two gas molecules on both sides

Question 15

Enthalpy change of exothermic reactions is ___

Answer 15

Negative

Question 16

Do exothermic reaction heat up or cool down a system?

Answer 16

Heat up

Question 17

Enthalpy change of endothermic reactions is ___

Answer 17

Positive

Question 18

Do endothermic reaction heat up or cool down a system?

Answer 18

Cool down

Question 19

True or false: If the forward reaction is exothermic, the backward reaction is also exothermic

Answer 19

False: If the forward reaction is exothermic, the backward reaction is endothermic and vice versa

Question 20

Increasing the temperature of a system of equilibrium

Answer 20

If the temperature is increased, the position of equilibrium will shift to oppose the change by moving in the endothermic direction and cool the system down.

Question 21

Decreasing the temperature of a system of equilibrium

Answer 21

If the temperature is decreased, the position of equilibrium will shift to oppose the change by moving in the exothermic direction and heat the system up.

Question 22

Effects of catalysts on the position equilibrium

Answer 22

Catalysts have no effect on the position of equilibrium. However, they do allow the position of equilibrium to be reached much quicker

Question 23

Effects of catalysts on the yield of products

Answer 23

They have no effect on the yield of any products as they do not affect the position of equilibrium

Question 24

Things to consider with equilibrium in industry

Answer 24

1. Yield
2. Equipment/Energy costs
3. Rate of reaction

Question 25

Equation for the Haber process

Answer 25

N2(g) + 3H2(g) ⇌ 2NH3(g)

Question 26

Is the forward reaction to create ammonia in the Haber process endothermic or exothermic?

Answer 26

Exothermic

Question 27

Conditions for the Haber process

Answer 27

20MPa (20000kPa) 450°C Iron Catalyst Recycle unused reactants

Question 28

Given that the forward reaction to create ammonia is exothermic, would the yield of ammonia be higher at 25°C or 250°C?

Answer 28

25°C because the position of equilibrium would shift to the right to heat the system up

Question 29

Why is a temperature of 450°C used in the Haber process if the yield is highest at a lower temp?

Answer 29

At a lower temp, the rate of reaction will be very low and ammonia is in high demand. 450°C is used as a compromise temp to have a sufficient rate which does not significantly inhibit the yield.

Question 30

Would the yield of ammonia be highest at a higher or lower pressure and why?

Answer 30

Higher, because there are less gas molecules on the right, so the position of equilibrium would shift to the right to make more ammonia and reduce the pressure

Question 31

Given that the yield of ammonia is highest at high pressures why isn't a pressure of >20MPa used in the Haber process?

Answer 31

Exerting higher pressures comes with much higher equipment and energy costs, and also safety concerns.

Question 32

Ammonia is cooled and removed from the reaction vessel. How does this increase the yield further?

Answer 32

Removing it decreases the concentration of ammonia, so the position of equilibrium shifts to the right to replace the ammonia that is being removed

Question 33

Conditions in the Haber process that reduce costs

Answer 33

- Compromise pressure of 20MPa - Recycling unused reactants - Iron catalyst, to increase the rate of reaction.

Question 34

Iron catalyst used in the Haber process is in pea sized lumps. How does this increase the rate of reaction?

Answer 34

Larger surface area of catalyst, providing more sites for reactant molecules to collide and react with the catalyst