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aqa physical chemistry > Electrochemistry > Flashcards

Electrochemistry Flashcards

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1
Q

What are electrochemical cells?

A

Batteries

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2
Q

What are electrochemical cells made up of?

A

Two half cells

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3
Q

What if a half cell usually made up of?

A
  • Solid metal (x) electrode- 1.0 mol.dm^-3 solution of (x) ions (aq)
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4
Q

What is set up in a half cell?

A

An equilibrium between x(s) and x ions (aq)

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5
Q

What can happen to a half cells equilibrium?

A

It can shift depending on the other half cell

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6
Q

What happens in the forward reaction of a half cell?

A
  • Reduction- Ions form the solid- Electrons enter from the other half cell
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7
Q

What happens in the reverse reaction of a half cell?

A
  • Oxidation- Solid forms the ions- Electrons leave to go to the other half cell
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8
Q

What can two half cells be combined to create?

A

A potential difference

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9
Q

How can you work out which half-cell is oxidised?

A
  • Put the most negative half cell on top- Top equation is oxidised
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10
Q

How can you work out which half-cell is reduced?

A
  • Put the most negative half cell on top- Bottom equation is reduced
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11
Q

Which half cell belongs on the LHS?

A

The one being oxidised

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12
Q

What happens at the LHS?

A
  • Oxidised- Annode- Negative
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13
Q

Which half cell belongs on the RHS?

A

The one being reduced

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14
Q

What happens at the RHS?

A
  • Reduced- Cathode- Positive
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15
Q

What conditions are half-cells combined at to form an electrochemical cell?

A
  • 298K- 100 kPa
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16
Q

What is needed to complete an electrochemical cell?

A

A salt bridge

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17
Q

What does a salt bridge do?

A

Completes the circuit

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18
Q

What is the REDOX power of a half-cell?

A

Relative

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19
Q

What is the REDOX potential of all the half-cells measured against?

A

The standard hydrogen electrode

20
Q

How do you calculate the electrode potential?

A

Connect a standard hydrogen electrode to another half cell and the potential difference is the other half cells electrode potential

21
Q

In the standard hydrogen electrode what is the electrode made of?

A

Platinum

22
Q

Why is the standard hydrogen electrode made of platinum?

A

Platinum is unreactive and porus and allows for easy electron transfer

23
Q

What is the electrode potential of the standard hydrogen electrode?

A

0.00v

24
Q

Why is the electrode potential of the standard hydrogen electrode 0?

A

Because it is compared to itself

25
Q

What happens if one half cell contains two ions in solution?

A
  • Both ions are present in the solution- Use a platinum electrode
26
Q

In the electrochemical series what is the most negative electrode potential?

A

Strongest reducing agent

27
Q

In the electrochemical series what is the most positive electrode potential?

A

Strongest oxidising agent

28
Q

What happens as electrode potential decreases?

A
  • Reducing power decreases- Further left the equilibrium lies- Easier it is to lose electrons- Easier to oxidise
29
Q

What happens as electrode potential increases?

A
  • Reducing power increases- Further right the equilibrium lies- Harder it is to lose electrons- Easier to reduce
30
Q

In electrochemical series what happens to the half-cell with the most negative electrode potential?

A

Oxidised

31
Q

In electrochemical series what happens to the half-cell with the most positive electrode potential?

A

Reduced

32
Q

How is EMF calculated?

A

Most positive electrode potential - most negative electrode potential or oxidised half cell value - reduced half cell value

33
Q

Which half cells will have the greatest EMF value?

A

Half cells with the largest difference in electrode potential

34
Q

Which half cells will have the smallest EMF value?

A

Half cells with the smallest difference in electrode potential

35
Q

With half-cells, which one will be the easiest to oxidise?

A
  • Most negative- Strongest reducing agent
36
Q

With half-cells, which one will be the easiest to reduce?

A
  • Most positive- Strongest oxidising agent
37
Q

What are the steps in using half cells to predict reactions?

A

1 - Write the half equations with the most negative on top2 - Add anticlockwise arrows ( left = oxidise, right = reduced )3 - Write equations in the correct direction4 - Balance equations5 - Combine

38
Q

What can the electrode potential be used to predict?

A

If a reaction is feasible

39
Q

How do you use electrode potentials to calculate the feasibility of a reaction?

A

1 - Most negative on top2 - Anticlockwise rule 3 - Underline reactants4 - If the reactants are on the top right and bottom left then the reaction will occur under standard conditions

40
Q

What are the limitations of using electrode potentials to calculate feasibility?

A
  • All electrode potential values are based off standard conditions- If conditions change the electrode potential values will change- Kinetics may be so slow that no real reaction is seen- Some reactions may not happen under standard conditions but will happen with higher concentrations or temperatures
41
Q

What are the standard conditions of an electrochemical cell?

A

298K, 100kPa, 1.0mol.dm^-3

42
Q

What can be used to make predictions when concentration or temperature is changed

A

Le chateliers principle

43
Q

How can a change in concentration effect the electrochemical cell value?

A
  • Increasing conc and/or decreasing product shifts the equilibrium to the right and the electrochemical cell value will increase - Decreasing conc and/or increasing product shifts the equilibrium to the left and the electrochemical cell value will decrease
44
Q

What is the deltaH value for the majority of electrochemical cells?

A

Negative - exothermic

45
Q

How can an increase in temperature effect exothermic cells?

A
  • Shift to the left- Favours endothermic- Against predicted route- Decrease electrochemical cell value
46
Q

How can a decrease in temperature effect exothermic cells?

A
  • Shift to the right- Favours exothermic- With predicted route- Increase electrochemical cell value

aqa physical chemistry (12 decks)

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