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Edexcel A-Level Chemistry > Chapter 10 - Chemical equilibrium (L) > Flashcards

Chapter 10 - Chemical equilibrium (L) Flashcards

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1
Q

What is chemical equilibrium?

A

When the forward and backwards reactions are occurring at equal rates

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2
Q

What 2 things must the reaction be for equilibrium to be reached?

A
  • The reaction must be closed (i.e. nothing being added or removed)
  • The reaction must be reversible
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3
Q

What is Le Chatelier’s principle?

A

If a reaction is at equilibrium, and the reaction conditions are then changed, the equilibrium position will shift in the direction that opposes the applied change

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4
Q

What are the 3 changes that affect position of equilibrium?

A
  • Pressure
  • Temperature
  • Concentration of reactants/products (material either added or removed)
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5
Q

What is the effect on equilibrium position when reactants are added?

A

Shifts to right to get rid of added reactants

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6
Q

What is the effect on equilibrium position when reactants are removed?

A

Shifts to left to produce more reactants

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7
Q

What is the effect on equilibrium position when product is added?

A

Shifts to left to get rid of added product

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8
Q

What is the effect on equilibrium position when product is removed?

A

Shifts to the right to produce more product

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9
Q

When do changes in pressure affect the position of the equilibrium?

A

For reactions that involve gases

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10
Q

What is the effect on equilibrium position when the temperature is increased on a forward exothermic reaction?

A

The equilibrium will move to the left (in the endothermic backwards direction) to lower the temperature

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11
Q

What is the effect on equilibrium position when the temperature is decreased on a forward exothermic reaction?

A

The equilibrium will move to the right (in the exothermic forward direction) to increase the temperature

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12
Q

What is the effect on equilibrium position when the pressure is increased?

A

The equilibrium will shift to the side with the fewer moles of gas to lower the pressure

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13
Q

What is the effect on equilibrium position when the pressure is decreased?

A

The equilibrium will shift to the side with more moles of gas

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14
Q

What is the effect on equilibrium position when the pressure is decreased?

A

The equilibrium will shift to the side with more moles of gas

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15
Q

What is the effect on equilibrium position when a catalyst is added?

A

There is no effect on the position of the equilibrium

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16
Q

What happens when a catalyst is added to a reaction in dynamic equilibrium?

A

The speed of both the forward and backwards reactions increase- it helps the reactions form equilibrium faster

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17
Q

What are heterogenous systems?

A

A system in which there are at least two different states present (e.g. gas + solid or liquid + aq)

18
Q

What are homogenous systems?

A

A system in which all components are the same state

19
Q

What factors affect the equilibrium constant?

A

The value of the equilibrium constant only changes if temperature changes- other changes e.g. pressure do not change the value

20
Q

What is the symbol for the value of equilibrium constant?

A

Kc

21
Q

In equilibrium law, what do the lower case letters represent?

A

The number of moles of the substance
e.g. 6H2O
The 6 would be the lower case

22
Q

In equilibrium law, what do the upper case letters represent?

A

The concentration of a given substance in the reaction
e.g. 6H2O
The 6 would be the lower case, and the concentration of H2O would be the upper case

23
Q

What is the formula for Equilibrium law i.e how do you work out Kc?

A

Kc =

[C]^c [D]^d
–––––––––
[A]^a [B]^b

24
Q

When Kc is significantly greater than 1, what does this indicate?

A

More product made than reactant

25
Q

When Kc is around 1, what does this indicate?

A

The amount of product made is roughly equal to the amount of reactant made

26
Q

When Kc is significantly less than 1, what does this indicate?

A

Very little product made- reaction barely starts

27
Q

What do you do with solids and liquids in equilibrium law and why?

A

You leave them out because their concentrations are constant/unchanging

28
Q

What the chemical equation for the manufacture of ammonia?

A

N2+ 3H2 - 2NH3

29
Q

What is the process used for manufacture of ammonia called?

A

The Haber process

30
Q

Which direction of the Haber process exothermic?

A

The forward reaction is exothermic

31
Q

What are the typical conditions of the Haber process?

A

450 degrees C and 250 atmospheres

32
Q

Why is a temperature of 450C used in the Haber process?

A

Too low of a temperature will mean the rate of reaction is too slow, and the catalyst will not be able to function efficiently
Too high of a temperature would be uneconomical due to energy costs, and may also result in a decreased ammonia yield (as the forward reaction is exothermic)
So a compromise temperature of 450C is used.

33
Q

Why will an increased pressure increase ammonia yield in the Haber process?

A

Because there is fewer moles of gas on the right than the left, so the equilibrium will shift to the products side with an increased pressure

34
Q

Why is a pressure of 250atm used in the Haber process?

A

The higher the pressure, the higher the ammonia yield, but also the higher the cost. So a compromise pressure of 250atm is used.

35
Q

What type of catalyst is most commonly used in industry for the Haber process?

A

An iron catalyst, as it is the cheapest

36
Q

What process is sulfuric acid manufactured by?

A

The Contact process

37
Q

Why is a temperature of 450C used in the Contact process?

A

For the same reasons as the Haber process-
too high = expensive and lower yield (due to exothermic forward reaction)
too low = slow rate of reaction + catalyst cannot work efficiently

38
Q

In the Contact process, what direction is endothermic?

A

Backwards

39
Q

What is the chemical formula for the production of sulfur trioxide in the Contact process?

A

SO2 + 1/2O2 - SO3

40
Q

What catalyst is used in the Contact process?

A

Solid vanadium oxide

41
Q

Why is a pressure of 2atm used in the Contact process?

A

Although in this reaction higher pressures = higher yields (as there are fewer moles on the right), at an atmosphere of just 1, the yield is already 97%. Therefore a pressure of 2atm is used, as any pressure higher than this would be unnecessary and a waste of money

Edexcel A-Level Chemistry (24 decks)

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