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Flashcards in Chemical Equilibrium Deck (63)
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1

What is a reversible reaction?

One in which the products can react again to reform the reactants A + B C + D

2

What is the name of this reaction: A + B = C + D

Forwards reaction

3

What is the name of this reaction: C + D = A + B

Backwards reaction

4

What is a closed system?

One where no reactants or products can escape

5

When is a dynamic equilibrium set up?

When a reversible reaction takes place in a closed system and eventually the rates of the forwards and backwards reactions will be the same

6

What does dynamic mean?

The forwards and backwards reactions are continuing and the rates of reaction are constant

7

What does equilibrium mean?

When the total amount of the species present remains the same

8

What is Le Chatelier's principle?

If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change

9

What happens during the reversible reaction of the dehydration of copper sulfate?

If you heat the blue copper sulfate crystals, it forms white anhydrous copper sulfate is formed and water is given off Anhydrous copper sulfate is used to test for the presence of water - if you add water to the white solid, it turns blue and heat is given off The original change has been exactly reversed. Even the heat has been given out again.

10

What is the equation of the dehydration of copper sulfate?

CuSO4.5H20 = CuSO4 + 5H2O

11

Is the dehydration of copper sulfate exothermic or endothermic?

Endothermic

12

What happens when you heat ammonium chloride?

If you heat ammonium chloride, the white crystals disappear form the bottom of the tube and reappear further up

Heating ammonium chloride splits it into the colourless gases ammonia and hydrogen chloride (sublimation)

These gases recombine further up the tube where it is cooler

The reaction reverses when the conditions are changed from hot to cool

13

What is the equation of the heating of ammonium chloride?

NH4Cl = NH3 + HCl

14

Is the heating of ammonium chloride exothermic or endothermic?

Endothermic

15

What is the effect of changing the concentration of the substances present (by adding more A (or B)) to increase the product?

This will favour the forwards reaction as the position of equilibrium will shift to counteract the change. The reaction will remove the extra A by producing more C and D.

16

What is the effect of changing the concentration of the substances present (by continuously removing C (or D)) to increase the product?

This will favour the forwards reaction as the position of equilibrium will shift to counteract the change. The reaction will react more A and B to replace the C that is being removed from the equilibrium.

17

How would you favour the exothermic reaction by changing the temperature?

Reduce the temperature. Exothermic reactions release heat into their surroundings, increasing the temperature of their surroundings. Therefore, if you reduce the temperature of the surroundings, the position of equilibrium will shift to counteract the change, by favouring the exothermic reaction, as this is what will increase the temperature.

18

How would you favour the endothermic reaction by changing the temperature?

Increase the temperature. Endothermic reactions absorb heat from their surroundings, decreasing the temperature of their surroundings. Therefore, if you increase the temperature of the surroundings, the position of equilibrium will shift to counteract the change, by favouring the endothermic reaction as this is what will decrease the temperature.

19

How would you favour the side with less moles by changing the pressure?

Reduce the pressure. The position of equilibrium will shift to counteract the change, by favouring the side with less moles, to produce more molecules, increasing the pressure.

20

How would you favour the side with more moles by changing the pressure?

Increase the pressure. The position of equilibrium will shift to counteract the change, by favouring the side with more moles, to produce less molecules, decreasing the pressure.

21

What is the equation for the Haber Process?

N2(g) + 3H2(g) = 2NH3(g)

DeltaH = -92kJ/mol

22

Is the Haber Process exothermic or endothermic?

Exothermic

23

Describe the Haber Process

N2 from the air + H2 from methane → Compressor (200atm) → Reaction Chamber with Iron Catalyst, ammonia gas formed in the reaction (450degrees) → Heat Exchanger - where heat is recycled → Condenser - ammonia gas turns into liquid ammonia and is then stored and the unreacted H2 and N2 gases go back to the reaction chamber and are recycled as they do not condense.

24

Why is the nitrogen and ammonia recycled?

Only about 15% of the nitrogen and ammonia combine each time so must be recycled.

25

What are the uses of ammonia?

Making fertilisers Making nitric acid

26

What is the reason for the iron catalyst in the Haber Process?

It speeds up both the forwards and backwards reaction Does not affect the yield of ammonia

27

What are the conditions needed for the Haber Process

Iron catalyst

200 atm

450 degrees

1 volume nitrogen to 3 volumes hydrogen

28

What is the reason for the pressure (200 atm) in the Haber Process?

There are 4 molecules on the LHS and 2 on the RHS. If you have a high pressure, the position of equilibrium will shift to favour the forwards reaction, as this will produce more ammonia, reducing the pressure, and increasing the yield of ammonia A high pressure also increases the rate of reaction But a higher pressure than 200atm is not used as it is expensive and dangerous

29

What is the reason for the temperature (450degrees) in the Haber Process?

The forwards reaction is exothermic, so releases heat into their surroundings, increasing the temperature of the surroundings. By having a low temperature, the position of equilibrium will shift to favour the forwards reaction, as it will increase the heat of the surroundings But a low temperature would greatly reduce the rate of the reaction, so a compromise temperature of 450 degrees is used which gives an acceptable rate of reaction

30

What is the reason for the constant removal of ammonia in the Haber Process?

It is removed by cooling and condensing it. This will decrease the concentration of gaseous ammonia, favouring the forwards reaction, as the position of equilibrium will shift to counteract the change to make more ammonia.