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Chemistry > 1.11 Redox Equilibria > Flashcards

1.11 Redox Equilibria Flashcards

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1
Q

Draw a simple electrochemical cell apparatus diagram.

A

(see page 1 in the chemrevise revision guide)

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2
Q

Why does a voltage form in an electrochemical cell?

A

(see page 1 in the chemrevise revision guide)

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3
Q

Why do we use a high resistance voltmeter in an electrochemical cell?

A

(see page 1 in the chemrevise revision guide)

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4
Q

Why do we use a salt bridge in an electrochemical cell?

What is it usually made of?

Why is a wire not used?

A

(see page 1 in the chemrevise revision guide)

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5
Q

What happens if a current is allowed to flow in an electrochemical cell?

A

(see page 1 in the chemrevise revision guide)

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6
Q

Draw the cell diagram of:

Zn(s) + (Cu)2+(aq) -> (Zn)2+(aq) + Cu(s)

A

(see page 2 in the chemrevise revision guide)

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7
Q

Draw the cell diagram of:

(Fe)2+(aq) -> (Fe)3+(aq) + e-

A

(see page 2 in the chemrevise revision guide)

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8
Q

Draw the cell diagram of:

(MnO4)- + 8H+ 5e- -> (Mn)2+ + 4H2O

A

(see page 2 in the chemrevise revision guide)

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9
Q

Draw the cell diagram of:

4e- + 2H2O(l) + O2(g) -> 4OH-(aq)

A

(see page 2 in the chemrevise revision guide)

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10
Q

Draw the cell diagram of:

Cl2(g) +2e- ->2Cl-

A

(see page 2 in the chemrevise revision guide)

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11
Q

How do you measure the electrode potential of a cell?

A

(see page 2 in the chemrevise revision guide)

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12
Q

How many volts is the standard hydrogen electrode assigned?

A

0 volts

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13
Q

Draw a standard hydrogen electrode apparatus diagram.

A

(see page 3 in the chemrevise revision guide)

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14
Q

Write the hydrogen electrode equilibrium equation.

A

(see page 3 in the chemrevise revision guide)

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15
Q

Draw the cell diagram of the standard hydrogen electrode.

A

(see page 3 in the chemrevise revision guide)

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16
Q

What are the 4 conditions of the standard hydrogen electrode?

A
  1. Hydrogen gas at pressure 100kPa
  2. Solution contains the hydrogen ion at 1.0moldm-3 (solution is usually 1M HCl)
  3. Temperature at 298K
  4. Platinum electrode
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17
Q

Why is a platinum wire used in a standard hydrogen electrode?

A

Because the equilibrium does not include a conducting metal surface, a platinum wire is used which is coated in finely divided platinum. (The platinum black is used because it is porous and can absorb the hydrogen gas)

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18
Q

Why are standard conditions needed for the standard hydrogen electrode?

A

Standard conditions are needed because the position of equilibrium will change with conditions.

(see page 3 in the chemrevise revision guide for example)

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19
Q

What is the standard electrode potential?

A

When an electrode system is connected to the hydrogen electrode system, and standard conditions apply the potential difference measured is called the standard electrode potential.

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20
Q

What are the standard cantons for a standard electrode potential?

A
  • All ion solutions at 1moldm-3
  • Temperature 298K
  • Gases at 100kPa pressure
  • No current flowing
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21
Q

Read the box labelled 1 on page 3 in the chemrevise revision guide.

A

understand?

22
Q

What are secondary standards when talking about SHE?

A

(see page 3 in the chemrevise revision guide)

23
Q

Give 2 common secondary standards.

A
  • silver / silver chloride

- calomel electrode

24
Q

What is the symbol for standard electrode potentials?

A

(see page 3 in the chemrevise revision guide)

25
Q

Give the equation for calculating the Ecell

A

Ecell = Erhs - Elhs

26
Q

What is the most useful application of electrode potentials?

A

To show the direction of spontaneous change for redox reactions.

27
Q

Answer the example Q 1 on page 5 in the chemrevise revision guide using information of page 4.

A

correct?

28
Q

Answer the example Q 2 on page 5 in the chemrevise revision guide using information of page 4.

A

correct?

29
Q

Answer the example Q 3 on page 5 in the chemrevise revision guide using information of page 4.

A

correct?

30
Q

Answer the example Q 4 on page 5 in the chemrevise revision guide using information of page 4.

A

correct?

31
Q

What is Ecell the measure of?

A

Ecell is a measure fo how far from equilibrium the cell reaction lies. The more positive the Ecell the more likely the reaction is to occur.

32
Q

If current is allowed to flow, what will happen to the value of Ecell?

A

If current is allowed to flow, the cell reaction will occur and the Ecell will fall to zero as the reaction proceeds and the reactant concentrations drop.

33
Q

Look at the equation in the box labelled 1 on page 6 in the chemrevise revision guide.

What would happen to the value of Ecell if you increased the concentration of (Fe)2+ and decreased the concentration of (Zn)2+?

A

Answer is below the labelled. box.

Correct?

34
Q

What would happen to the value of Ecell if you increased the temperature on an exothermic reaction equilibrium?

A

(see page 6 in the chemrevise revision guide)

35
Q

If the Ecell is positive what does this indicate?

A

If the Ecell is positive it indicates. a reaction might occur. There is still a possibility, however, that the reaction will not occur or will occur so slowly that effectively it does not happen.

If the reaction has a high activation energy the reaction will not occur.

36
Q

Is the reaction reversible or irreversible:

  • non-rechargeable cells
  • rechargeable cells
A

non-rechargeable, irreversible

rechargeable, reversible

37
Q

What is the value of Ecell for the example Q labelled 2 on page 6 in the chemrevise revision guide?

A

correct?

38
Q

What is the value of Ecell for the example Q labelled 3 on page 6 in the chemrevise revision guide?

A

correct?

39
Q

What is the value of Ecell for the example Q labelled 4 on page 6 in the chemrevise revision guide?

A

correct?

40
Q

What is the value of Ecell for the example Q labelled 5 on page 7 in the chemrevise revision guide?

A

correct?

41
Q

What is the value of Ecell for the example Q labelled 6 on page 7 in the chemrevise revision guide?

A

correct?

42
Q

How do fuel cells create a voltage?

A

A feel cell uses the energy from the reaction of a fuel with oxygen to create a voltage.

43
Q

What is the value of Ecell for the example Q labelled 7 on page 7 in the chemrevise revision guide?

A

correct?

44
Q

Why do fuel cells maintain a constant voltage over time?

A

Fuel cells will maintain a constant voltage over time because they are continuously fed with fresh O2 and H2 so maintaining constant concentration of reactants. This differs from ordinary cells where the voltage drops over time as the reactant concentrations drop.

45
Q

Why do you not use standard conditions in fuel cells?

A

When you use standard conditions, the rate is too slow to produces an appreciable current.

A higher temperature is therefore used to increase the rate but the reaction is exothermic so by applying le Chatelier would mean the Ecell falls.

A higher pressure can help counteract this.

46
Q

Draw a fuel cell apparatus diagram.

A

(see page 7 in the chemrevise revision guide)

47
Q

What are the 2 advantages of fuel cells over conventional petrol or diesel-powered vehicles?

A

1) Less pollutions and less CO2 (pure hydrogen emits only water whilst hydrogen-right fuels produce only small amounts of air pollutants and CO2)
2) Greater efficiency

48
Q

What are the 4 limitations of hydrogen fuel cells?

A

1) expensive
2) Storing and transporting hydrogen, in terms of safety, feasibility of a pressurised liquid and a limited life cycle of a solid ‘absorber’.
3) Limited lifetime (requiring regular replacement and disposal) and high production costs
4) Use of toxic chemicals in their production

49
Q

What 3 different ways can hydrogen be stored in fuel cells?

A
  1. As a liquid under pressure.
  2. Absorbed on the surface of a solid material.
  3. Absorbed within a solid material.
50
Q

What are 4 advantages of ethanol fuel cells over hydrogen fuel cells?

A
  1. Ethanol can be made from renewable sources in a. carbon neutral way.
  2. Raw materials to produce ethanol by fermentation are abundant.
  3. Ethanol is less explosive and easier to store than hydrogen.
  4. New petrol stations would not be required as ethanol is a liquid fuel.
51
Q

Give the overall equation for the reaction that occurs in an ethanol fuel cell.

A

(see page 8 in the chemrevise revision guide)

52
Q

What would happen the the value of Ecell if you increased the concentration of reactants?

A

Increasing concentration of reactants would increase Ecell and decreasing them would cause Ecell to decrease.

Chemistry (36 decks)

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