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Physical chemistry 2 > Electrode Potentials And Electrochemical Cells > Flashcards

Electrode Potentials And Electrochemical Cells Flashcards

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1
Q

How do we get electricity?

A

By the movement of electrons

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2
Q

What type of cells make electricity

A

Electrochemical cells make electricity

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3
Q

How are electrochemical cells made?

A

• Made from two different metals dipped in salt solutions of their own ions and connected by a wire (the external circuit)

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4
Q

How many reactions are in an electrochemical cell?

A

• Oxidation
• Reduction
• Redox processes

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5
Q

How do electrons flow in an electrochemical cell?

A

Electrons flow through the wire from the more reactive metal to the less reactive one

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6
Q

What is the use of a voltmeter

A

• Found in the external circuit
• Used to measure the voltage between the two half-cells
• Finds the cell potential or electromotive force known as Ecell

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7
Q

What other variations of half-cells are possible?

A

• Half cells involving solutions of two aqueous ions of the same element.

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8
Q

Why is a platinum electrode used?

A

Platinum is an inert gas so it does not react with ions

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9
Q

What type of reaction happens at each electrode

A

Reversible reactions

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10
Q

What does the reversible arrow show?

A

That both reactions of each electrode can go in either directions (the flow of electrons)

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11
Q

How are half-equations for electrochemical cells written

A

• They’re always written with the reduction reaction going forward direction (with the electrons on the left-hand side)

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12
Q

What is the condition dependent on which direction the reaction will go in

A

• The reaction depends on on how easily each metal looses electrons ( how easily it’s oxidised)

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13
Q

What is the function of electrode potentials

A

• Measure how easily metals are oxidised
• A metals that’s easy to oxidise has a very negative electrode potential. One that’s harder to oxidise has a less negative (or positive) electrode potential

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14
Q

What are the guideline for wiring the overall equation for a cell

A

• Reduced means the half equation goes forward
• Oxidised means the half equation goes backwards

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15
Q

List the conditions that affect cell potentials

A

• Temperature
• Pressure
• Concentration

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16
Q

What is the standard electrode potential of a half cell?

A

The standard electrode potential of a half cell is the voltage measured under standard conditions when the half-cell is connected to a standard hydrogen electrode

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17
Q

What are the standard conditions for a half-cell?

A

• Any solutions must have a concentration of 1.00mol dm-3
• The temperature must be 298K (25C)
• The pressure must be 100kPa

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18
Q

Note

A

Is standard conditions are maintained, the reading in the voltmeter when a half-cell is connected to the standard hydrogen electrode will be the standard electrode potential of that half-cell

19
Q

What is the function of the salt bridge

A

• Connects the solutions
• Made from filter paper soaked in KNO3(aq)
• Allows ions to flow through and balance out the charges

20
Q

What is the function of the electrochemical series

A

It shows you what elements are reactive and which are not

21
Q

What is an electrochemical series

A

An electrochemical series is basically a list of standard electrode potentials for different electrochemical half-cells

22
Q

What can be calculated from the electrochemical series

A

Standard cell potentials

23
Q

What is the function of a standard electrode potential

A

Standard electrode potential values can be used to calculate the standard cell potential Ecell or (EMF: electromotive force) when two half-cells are joined together.

24
Q

Give the equation for the EMF of a cell

A

Ecell= Ereduced - Eoxidised

25
Q

What is the first step in calculating the EMF

A

L First write the two half equations down as reduction reactions and write their E/V value from the electrochemical series

26
Q

Describe the shorthand way of drawing electrochemical cells

A

• The half cell with a more negative potential goes on the left
• The oxidised forms go in the centre of the cell diagram

27
Q

What do electrode potentials predict?

A

Whether a reaction will happen

28
Q

What do the vertical lines on n a shorthand electrochemical cell show?

A

Double lines show a salt bridge

29
Q

The more negative the electrode is, the more…..

A

Reactive the metal will be

30
Q

What happens to metals when they react?

A

They loose electrons, they become oxidised

31
Q

Give one advantage and one disadvantage of non-rechargeable batteries

A

• They are cheaper however,
• They cannot be recharge

32
Q

Name a metal that is used in the electrodes in an alkaline hydrogen-oxygen fuel cell

A

Platinum containing electrodes

33
Q

What electrolyte is used in an alkaline hydrogen-oxygen fuel cell?

A

Aqueous alkaline solution (OH-)

34
Q

How is a lithium battery recharged vs a non-rechargeable battery

A

• To recharge these batteries, a current is supplied to force electrons to flow in the opposite direction around the circuit
• And reverse the reactions
• The reactions that take place in non-rechargeable batteries are difficult or impossible to reverse in this way

35
Q

What happened to the half equations in a rechargeable batteries

A

The reactions are reversed

36
Q

Give one type of electrochemical cells which provide electricity

A

Batteries

37
Q

Give some types of batteries, their advantages and disadvantages

A

•Non-rechargeable batteries: can only be used until they run out. They are cheaper.

• Rechargeable batteries: Last longer and are cheaper in the long-run

38
Q

What type of cells are used in mobile phones and laptops

A

Lithium cells

39
Q

Describe how lithium cells provide electricity

A

• Lithium cell is made up of a lithium cobalt oxide (LiCoO2) and a graphite electrode
• The electrolyte is a lithium salt in an organic solvent
• Half equations: Check digital flashcards 🔴
• The Li+/ Li half cell has the more negative E value so goes in the direction of oxidation (backwards)
• The reaction that happens at the battery supplies, positive and negative electrode: Check did vital flashcards for answers🔴🔴

40
Q

How do fuel cells generate electricity and give examples

A

• Chemicals that generate electricity are contained in the electrodes and the electrolyte that form the cell
• Chemicals are stored separately outside the cell and are fed in when electricity is needed
• alkaline hydrogen-oxygen fuel cell, used to power electric vehicles
• Hydrogen and oxygen gases are fed into two separate platinum-containing electrodes
• The electrodes are separated by an anion-exchange membrane that allows (OH-) and water to pass through it but not hydrogen and oxygen gases
• The electrolyte is an aqueous alkaline KOH solution
• Electrons flow from the negative circuit through an external circuit to the positive electrode
• The OH- ions pass through the anion-exchange membrane towards the negative electrode

41
Q

Why do fuel cells have big advantages?

A

• using fuel cells in cars is more efficient
• able to convert more of their available energy into kinetic energy to get the car moving
• Internal combustion engines waste a lot of their energy producing heat
• Fir fuel cells the only waste product is water so no nasty toxic chemicals to dispose of and no carbon emissions
• Fuel cells don’t need to be recharged like batteries. As long as hydrogen and oxygen are supplied the cell will continue to produce electricity

42
Q

What are some disadvantages of fuel cells

A

• Energy is needed to supply hydrogen and oxygen
• They can be produced from the electrolysis of water e.g.
• Re-using the waste product from the fuel cell but this requires electricity
• This electricity is generated by burning fossil fuels
• The whole process isn’t usually carbon neutral
• Hydrogen is also highly flammable, it needs to be handled carefully when it is stored or transported

43
Q

What is the overall effect of alkaline hydrogen-oxygen fuel cell

A

Hydrogen and oxygen react to make water

44
Q

Agents on the left hand side of the electrochemical series are more easily?

A

Reduced, so oxidising agents

Physical chemistry 2 (7 decks)

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