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Chemistry 3 + 4 > Chapter Three : Converting chemical energy to electrical energy > Flashcards

Chapter Three : Converting chemical energy to electrical energy Flashcards

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1
Q

Redox reactions definition

A

Reactions that involve the transfer of one or more electrons between chemical species

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2
Q

Reduction definition

A

A decrease in oxidation number; a gain of electrons

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3
Q

Oxidation definition

A

An increase in the oxidation number; a loss of electrons

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4
Q

Oxidising agents definition

A

Electron acceptors

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5
Q

Reducing agents

A

Electron donors

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6
Q

Galvanic cells

A

Consists of

  • 2 half cells with an anode and cathode
  • a conducting wire (external circuit)
  • a salt bridge (internal circuit)
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7
Q

Cathode

A

Positive electrode
Reduction occurs here
Strongest oxidising agent

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8
Q

Anode

A

Negative electrode
Oxidation occurs here
Strongest reducing agent

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9
Q

Three types of half cells

A

Metal ion-metal half cell
The solution half cell
The gas-non-metal half-cell

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10
Q

The metal ion-metal half cell

A 
Contains a metallic electrode
Ion solution (ion of metal)
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11
Q

The solution half cell

A

Inert electrode

Solution with 2 ions

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12
Q

The gas-non-metal ion half cell

A

Inert electrode
Gas bubbled into solution
Ions of the gas in solution

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13
Q

Standard electrode potential definition

A

Potential to gain an electron

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14
Q

Electronic potential definintion

A

The ability of the cell to produce an electric current

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15
Q

The reduction potential definition

A

Is a measure of the tendency of an oxidising agent to accept electrons

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16
Q

Standard cell potential difference definition

A

The measured cell potential difference under standard conditions

17
Q

Cell potential difference equation

A

E cell = E oxidising agent - E reducing agent

18
Q

The unpredictability of rate of reaction

A

Although reactants may be spontaneous they may nt happen quickly
If conditions are too different from the standard it could change the order of the electrochemical series

19
Q

Primary cells definition

A

A cell in which the cell reaction is not reversible

20
Q

Secondary cells definition

A

Cells in which the cell reaction is reversible

21
Q

Examples of non rechargeable cell

A

Dry cell
Button cell
Alkaline cell

22
Q

Examples of rechargeable cell

A

Lithium ion

Lead-acid

23
Q

Examples of fuel cells

A

Hydrogen-oxygen

Methane-oxygen

24
Q

Factors affecting selection of cells

A 
Initial and operating cost
Size and shape
Mass
Memory effect
Voltage provided
Discharge curve
Current
Shelf life
Ease of disposal
Environmental issues
25
Q

Fuel cells

A

An electrochemical device that converts chemical energy into electrical energy

26
Q

Design of fuel cell

A 
Anode and cathode are in the same cell
Porous electrodes
Reactants are often gases
Oxygen is always at cathode
H+ means cell is acidic
OH- means cell is alkaline
27
Q

Acidic fuel cell reactants

A

H+, H2O, H2, O2

28
Q

Alkaline fuel cell reactants

A

OH-, H2O, O2, H2

29
Q

Anode and cathode change

A

Cathode increases in mass as cell functions

Anode remains unchanged as cell functions

30
Q

Why is a fuel cell compared to power station?

A

Multistep process in the factory

Gas has to combust, trun the tubine etc.

31
Q

Advantages of fuel cells

A

High energy conversion efficiency
Low chemical pollution
Fuel flexibility

32
Q

Disadvantages of fuel cells

A

Manufacturing process and materials are expensive
Need a reliable and continuous supply of fuel
Distribution and storage of hydrogen

33
Q

Purpose of porous electrodes

A

Maximise surface area available for the electrode reaction, increasing rate of reaction and current output. doesnt increase cell p or voltage

34
Q

How to increase the rate of reaction in a fuel cell

A

Making electrodes porous

Using electrodes that also catalyse the reaction

35
Q

What happens when galvanic cells are in the same cell?

A

The identical reactions still occur but the electrons travel directly rather than in an external circuit
Energy is released as heat rather than being converted to electrical energy

Chemistry 3 + 4 (12 decks)

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