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AQA Physical Chemistry > Chemical Equilibria > Flashcards

Chemical Equilibria Flashcards

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1
Q

What does le chateliers help to predict?

A

The shift in equilibrium when conditions are changed

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2
Q

What is le chateliers principle?

A

If the conditions of a dynamic equilibrium in a closed system are changed the equilibrium will shift to oppose that change

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3
Q

What are the conditions that can effect equilibrium?

A

Concentration, temperature, pressure

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4
Q

What is a closed system?

A

No reactants/products can escape

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5
Q

What effect does a catalyst have on the position of equilibrium?

A

A catalyst will have no effect on the position of equilibrium buy a system will reach equilibrium more quickly

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6
Q

What happens at the beginning of a dynamic equilibrium?

A

The reactants react to form the products

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7
Q

What happens as an equilibrium proceeds?

A

The products react to reform the reactants

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8
Q

When is a dynamic equilibrium set up?

A

When the rate of the forward reaction is equal to the rate of the reverse reaction and the relative concentrations of the reactants and products remain constant

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9
Q

What must the reaction take place for a dynamic equilibrium to be achieved?

A

Reaction must take place in a closed system

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10
Q

What happens if the point of equilibrium is in the middle?

A

Products and reactants will reach equilibrium with the same concentration

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11
Q

What happens if the point of equilibrium is to the right?

A

The products are favoured and equilibrium will be reached with the products having a greater concentration than the reactants

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12
Q

What happens if the point of equilibrium is to the left?

A

The reactants are favoured and equilibrium will be reached with the reactants having a greater concentration than the products

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13
Q

What are the indicators that a reaction has reached equilibrium?

A

The concentration, colour, density and pressure are all constant

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14
Q

(Concentration) When will equilibrium shift to the right?

A

if the concentration of the reactants increases or the concentration of the products decreases

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15
Q

(Concentration) When will equilibrium shift to the left?

A

if the concentration of the products increases or the concentration of the reactants decreases

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16
Q

What happens to the equilibrium if the concentration of a reactant is increased?

A
  • Equilibrium shifts to the right- More reactants reacted together to produce more product- As a result the initial change is opposed- other reactant concentrations are decreased but the products concentrations increase
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17
Q

What happens to the equilibrium if the concentration of a reactant is decreased?

A
  • Equilibrium shifts to the left- More product is reacted to produce more reactant- as a result the product concentration is lowered and the initial change is opposed - The product concentrations are lowered but the reactant concentrations increase
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18
Q

When will a change in pressure effect equilibrium position?

A

It will only effect dynamic equilibria that contain at least one gas

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19
Q

What is the prediction of shift (pressure) dependent on?

A

Number of moles of gas on each side of the equilibrium

20
Q

What happens to equilibrium position if pressure is increased?

A
  • Side with the fewest moles of gas is favoured- Equilibrium opposes the change by favouring the reaction that reduces the number of moles of gas - Pressure is lowered
21
Q

What happens to equilibrium position if pressure is decreased?

A
  • Side with the greatest moles of gas is favoured- Equilibrium opposes the change by favouring the reaction that increases the number of moles of gas - Pressure is increased
22
Q

What happens to the position of equilibrium if pressure is changed but both sides of the equation have an equal number of moles?

A

Changes in pressure will have no effect on equilibrium position

23
Q

As well as equilibrium position, what can pressure changes also affect?

A

Rate

24
Q

When predicting the effect of changing the temperature on equilibrium what is the prediction dependent on?

A

The delta H value

25
Q

What does a positive delta H suggest?

A

Reaction is endothermic

26
Q

What does a negative delta H suggest?

A

Reaction is exothermic

27
Q

What effect does an increase in temperature have on the position of equilibrium?

A
  • Favours the endothermic reaction- Equilibrium favours the reaction that absorbs heat energy - Temperature is lowered
28
Q

What effect does a decrease in temperature have on the position of equilibrium?

A
  • Favours the exothermic reaction- Equilibrium favours the reaction that releases heat energy - Temperature is increased
29
Q

What happens to an equilibrium when temperature is changed but delta H = 0?

A

Changes to temperature will have no effect on equilibrium

30
Q

As well as equilibrium, what can changes in temperature also affect?

A

Rate of reaction

31
Q

What does the hater process produce?

A

Gaseous ammonia

32
Q

What are the reactants in the haber process?

A

Nitrogen gas and hydrogen gas

33
Q

What reactant concentrations are used during the haber process and how do they compare with the ideal conditions?

A

Ideally reactant concentrations should be high to push the equilibrium to favour the products and increase the yield of ammonia. This is achieved in industry by recycling the unused nitrogen and hydrogen to maintain the high concentrations

34
Q

What product concentrations are used during the haber process and how do they compare with the ideal conditions?

A

Ideally low product concentrations will be used to push the equilibrium to favour the products and increase their yield. This is achieved in industry by cooling the products and condensing them off to maintain a low concentration

35
Q

What temperature conditions are used during the haber process and how do they compare with the ideal conditions?

A

A low temp would be ideal because the forward reaction is exothermic and a low temperature will favour the exothermic reaction and increase the ammonia yield. However, this cannot be achieved in industry because low temperature decrease the rate of the reaction. A compromise temperature Is used to balance rate and yield

36
Q

What pressure conditions are used during the haber process and how do they compare with the ideal conditions?

A

A very high pressure would be ideal because that will favour the side with the fewest moles of gas (products) and increase the yield of ammonia and the rate at which it is produced. However, high pressures can be very expensive and dangerous so a compromise pressure is used to balance yield and rate with safety and cost

37
Q

What catalyst is used in the Haber process and why?

A

A solid Iron catalyst is used (heterogeneous) it offsets the effect of the compromise temperatures and pressures and increases the rate

38
Q

What does Kc do?

A

Describes the state of the homogeneous equilibrium with respect to the concentrations of the reactants and products

39
Q

What is the Kc expression?

A

Concentration of the products each to the power of their number of moles divided by the concentration of the reactants each to the power of their number of moles

40
Q

What are the units of concentration?

A

mol.dm^-3

41
Q

What does it mean is Kc = 1?

A

Equilibrium lies exactly in the middle

42
Q

What does it mean if Kc < 1?

A

Equilibrium lies to the left

43
Q

What does it mean if Kc > 1?

A

Equilibrium lies to the right

44
Q

Which factor will affect Kc?

A

Temperature

45
Q

What happens to a reaction if temperature is increased?

A

Endothermic reaction is favoured

46
Q

What happens to a reaction if temperature is decreased?

A

Exothermic reaction is favoured

AQA Physical Chemistry (12 decks)

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