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Chemistry > 1.6 Equilibria > Flashcards

1.6 Equilibria Flashcards

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1
Q

Define the term dynamic in a dynamic equilibrium.

A

The term dynamic means both forward and backward reactions are accruing simultaneously.

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2
Q

Give two features of a dynamic equilibrium.

A
  1. Forward and backward reactions are occurring at equal rates.
  2. The concentrations of reactants and products stays constant.
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3
Q

What does Le Chatelier’s principle state?

A

Le Chatelier’s principle states that is an external condition is changed the equilibrium will shift to oppose the change.

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4
Q

What will happen to the position of equilibrium if the temperature is increased?

A

If temperature is increased the equilibrium will shift to oppose this and move in the endothermic direction to try to reduce the temperature by absorbing heat.

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5
Q

What will happen to the position of equilibrium if the temperature is decreased?

A

If temperature is decreased the equilibrium will shift to oppose this and move in the exothermic direction to try to increase the temperature by giving out heat.

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6
Q

Answer the typical exam question 1 on page 1 in the chemrevise revision guide.

A

correct?

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7
Q

What will happen to the position of equilibrium if the pressure is increased?

A

Increasing pressure will cause the equilibrium to shift towards the side with fewer moles of gas to oppose change and thereby reduce the pressure.

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8
Q

What will happen to the position of equilibrium if the pressure is decreased?

A

Decreasing the pressure will cause the equilibrium to shift towards the side with more moles of gas to oppose the change and thereby increase the pressure.

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9
Q

What will happen to the position of equilibrium if the pressure is changed when there are equal number of moles of reactants and products?

A

If the number of moles of gas is the same on both sides of the equation then changing the pressure will have no effect on the position of equilibrium.

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10
Q

Answer the typical exam question 2 on page 1 in the chemrevise revision guide.

A

correct?

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11
Q

What is the advantage of increasing the pressure on equilibrium reactions in industry?

A

Increasing the pressure may give a higher yield of product and will produce a faster rate.

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12
Q

What is the disadvantage of increasing the pressure on equilibrium reactions in industry?

A

Industrially high pressures are expensive to produce:

  • High electrical energy costs for pumping the gases to make a high pressure.
  • The equipment is expensive to contain the high pressures.
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13
Q

If the forward reaction is exothermic, how would a low temperature effect the yield of product? What is the problem with this?

A

Low temperatures may give a higher yield of product if the forward reaction is exothermic but will also result in slow rated of reaction. Often a compromise temperature is used that gives a reasonable yield and rate.

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14
Q

What effect would increasing the concentration of OH- ions have on this reaction?

I2 + 2OH- I- + IO- + H2O
brown to colourless

A

Increasing the concentration of OH- ions causes the equilibrium to shift to oppose this and move in the forward direction to remove and decrease the concentration of OH- ions. The position of equilibrium will shift towards the right, giving a higher yield of I- and IO-. (the colour will change from brown to colourless.

Adding H+ ions reacts with the OH- ions and reduces their concentration so the equilibrium shifts back to the left giving brown colour.

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15
Q

What effect does adding a catalyst to an equilibrium reaction have?

A

A catalyst has no effect on the position of equilibrium, but it will speed up the rate at which the equilibrium is achieved.

It does not effect the position of equilibrium because it speeds up the rates of the forward and backward reactions by the same amount.

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16
Q

Give the equation of the Haber process.

A

(see page 2 in the chemrevise revision guide)

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17
Q

In industry, what temperature and pressure is used on the Haber process and why?

∆H = -ve
exothermic
T = 450ºc
P = 200-1000atm
catalyst = iron
A
  • A low temperature gives a good yield but a slow rate: A compromise temperature is used.
  • A high pressure gives a good yield and a high rate: Too high a pressure would lead to too high energy costs for pumps to produce the pressure.
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18
Q

Give the equation for the production of methanol from CO.

A

(see page 2 in the chemreivse revision guide)

19
Q

In industry, what temperature and pressure is used on the production of methanol from CO and why?

∆H = -ve
exothermic
T = 400ºc
P = 50 atm
catalyst = chromium and zinc oxides
A
  • Low temp gives good yield but slow rate: compromise temperature is used.
  • High pressure gives good yield and high rate: Too high pressure would lead to too high energy costs for pumps to produce the pressure.
20
Q

Give the equation for the hydration of ethene to produce ethanol.

A

(see page 2 in the chemrevise revision guide)

21
Q

In industry, what temperature and pressure is used on the hydration of ethene to produce ethanol and why?

∆H = -ve
T = 300ºc
P = 70atm
catalyst = conc H3PO4
A
  • Low temperature gives good yield but slow rate: compromise temp is used.
  • High pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure.
  • High pressure also leads to unwanted polymerisation of ethene to poly(ethene)
22
Q

Why is a catalyst used in an equilibrium reaction?

A

Catalysts speed up the rate, allowing a lower temperature to be used and hence lower energy costs.

(they have no effect on position of equilibrium)

23
Q

Why do industry recycle unreacted reactants?

A

Recycling unreacted reactants back into the reactor can improve the overall yield.

24
Q

What does carbon neutral mean?

A

The term carbon neutral refers to “an activity that has no net annual carbon (greenhouse gas) emissions to the atmosphere”

25
Q

Give the Kc equation for a generalised equation of:

mA + nB pC + qD

(m,n,p,q are the stoichiometric balancing numbers)

(A,B,C,D stand for the chemical formula)

A

(see page 3 in the chemrevise revision guide)

26
Q

Give the Kc of the equation:

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

Giving the units the answer would be in.

A

(see page 3 in the chemrevise revision guide)

27
Q

Give the Kc of the equation:

H2(g) + Cl2(g) 2HCl(g)

Giving the units the answer would be in.

A

(see page 3 in the chemrevise revision guide)

28
Q

Answer Example 3 on page 3 in the chemrevise revision guide.

A

correct?

29
Q

What does Kc stand for?

A

The equilibrium constant.

30
Q

Give the equation to calculate the moles of reactant at equilibrium.

A

moles of reactant at equilibrium = initial moles - moles reacted

31
Q

Give the equation to calculate the moles of product at equilibrium.

A

moles of product at equilibrium = initial moles - moles formed

32
Q

Answer Example 4 on page 3 in the chemrevise revision guide.

A

correct?

33
Q

If the value of Kc is large, what does that tell us about the amount of product formed?

A

The larger the Kc the greater the amount of products.

34
Q

If the value of Kc is small, what does that tell us about the amount of product formed?

A

If Kc is small the equilibrium favours the reactants.

35
Q

Does temperature affect the value of Kc?

A

Yes, both the position of equilibrium and the value of Kc will change if the temperature is altered.

36
Q

Does pressure affect the value of Kc?

A

No, the position of equilibrium will change if the pressure is altered but the value of Kc stays constant as Kc only varies with temperature.

37
Q

Does presence of a catalyst affect the value of Kc?

A

No, catalysts have no effect on the value of Kc or the position of equilibrium as they speed up both forward and backward rates by the same amount.

38
Q

Answer Example 5 on page 5 in the chemrevise revision guide.

A

correct?

39
Q

Describe the method for working out the equilibrium constant Kc.

A common experiment is working out the equilibrium constant for an esterification reaction. Ethanol and ethnic acid are mixed together with a sulphuric acid catalyst. (write the equation for this reaction)

A

(see page 6 in the chemrevise revision guide)

40
Q

Give the equation for calculation moles with density and volume.

A

moles = density x volume

41
Q

Answer the question labelled 1 on page 6 in the chemrevise revision guide.

A

correct?

42
Q

Answer the question labelled 2 on page 7 in the chemrevise revision guide.

A

correct?

43
Q

Answer the question labelled 3 on page 7 in the chemrevise revision guide.

A

correct?

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