Galvanic Cells as a Source of Energy

Question 1

Describe an electrochemical cell

Answer 1

Device in which chemical energy is converted into electrical energy, or vice versa

Question 2

Describe a galvanic cell

Answer 2

Electrochemical cell in which chemical energy is converted into electrical energy.

Question 3

Provide an alternative term to describe a galvanic cell

Answer 3

Voltaic cell

Question 4

State what a salt bridge is often made from

Answer 4

Filter paper soaked in a relatively unreactive electrolyte (e.g. potassium nitrate solution)

Question 5

State an early form of the galvanic cell

Answer 5

Daniell Cell

Question 6

Describe an electrolyte

Answer 6

A chemical substance that conducts electric current as a result of dissociation into positively and negatively charged ions, which migrate toward the negative and positive terminals of an electric circuit.

Question 7

Describe an electrode

Answer 7

A solid conductor in a half-cell at which oxidation or reduction reactions occur.

Question 8

Describe electrolysis

Answer 8

Process that produces a non-spontaneous redox reaction by the passage of electrical energy from a power supply through a conducting liquid.

Question 9

State whether a metal displacement reaction in a Daniell Cell is spontaneous or non-spontaneous

Answer 9

Spontaneous

Question 10

Describe half-cell

Answer 10

Half of an electrochemical cell.

Question 11

State what the species present in each half cell forms

Answer 11

A conjugate redox pair

Question 12

Describe a conjugate redox pair

Answer 12

Oxidising agent and the reducing agent that is formed when the oxidising agent gains electrons

Question 13

State what half cells usually contain

Answer 13

Other species that are not involved in the reaction (e.g. spectator ions or a solvent)

Question 14

State the term used to identify the electrode at which oxidation occurs

Answer 14

Anode

Question 15

State the term used to identify the electrode at which reduction occurs

Answer 15

Cathode

Question 16

State what terminal the anode of a galvanic cell is considered

Answer 16

Negative

Question 17

State what terminal the cathode of a galvanic cell is considered

Answer 17

Positive

Question 18

State the purpose of a salt bridge in a galvanic cell

Answer 18

Contains ions that are free to move so that they can balance charges formed in the two compartments

Question 19

State to what terminal cations move towards

Answer 19

Cathode

Question 20

State to what terminal anions move towards

Answer 20

Anode

Question 21

State what would occur to the conditions within a galvanic cell if a salt bridge was not present

Answer 21

Solution in one compartment - accumulate negative charge

Solution in other compartment - accumulate positive charge

Question 22

State an alternative term associated with the salt bridge

Answer 22

Internal circuit

Question 23

State what affect the accumulation of charge in one or both compartments of the galvanic cell (in the absence of a salt bridge) would have on the reaction

Answer 23

Stop reaction and prevent further reaction

Question 24

State what a metal displacement reaction is an example of

Answer 24

Spontaneous exothermic reaction

Question 25

State what a metal displacement reaction could be identified as if the reactants are allowed to come into direct contact with one another

Answer 25

Spontaneous exothermic reaction - chemical energy is transformed directly to thermal energy

Question 26

State whether a metal displacement reaction in a galvanic cell can be classified as a spontaneous exothermic reaction

Answer 26

No. The reactants do not come in contact with one another therefore a chemical-thermal energy transformation cannot occur. (Instead a chemical-electrical transformation occurs).

Question 27

State what cells and batteries use as their source of energy

Answer 27

Spontaneous redox reactions

Question 28

State the 2 basic types of cells

Answer 28

1. Primary cells - disposable and designed not to be recharged 2. Secondary cells - rechargeable and designed to be reused many times

Question 29

State what both primary and secondary cells can be classified as

Answer 29

Galvanic cells

Question 30

State whether commercial alkaline cells are considered rechargeable or non-rechargeable cells

Answer 30

Non-rechargeable cells

Question 31

State what must occur for commercial alkaline cells to 'go flat'

Answer 31

Reaction reaches equillibrium

Question 32

State what cells that cannot be recharged are considered

Answer 32

Primary cells

Question 33

State what cells that are designed to be recharged are considered

Answer 33

Secondary cells

Question 34

Provide 2 examples of rechargeable cells

Answer 34

1. Lithium-ion cells | 2. Nickel-metal hydride cells

Question 35

State whether lithium-ion cells and nickel-metal hydride cells are considered rechargeable or non-rechargeable

Answer 35

Rechargeable cells

Question 36

State how a rechargeable cell is recharged

Answer 36

Cell reaction must occur in reverse (the products of the reaction must be converted back into the original reactants)

Question 37

State to which electrode of a rechargeable battery the positive terminal of a charger is connected to

Answer 37

Positive electrode

Question 38

State to which electrode of a rechargeable battery the negative terminal of a charger is connected to

Answer 38

Negative electrode

Question 39

State what electrical energy supplied by the charger is converted into

Answer 39

Chemical energy in the cell

Question 40

State what must occur in order to regenerate the reactants of a rechargeable cell

Answer 40

Products formed in the cell during discharge must remain in contact with the electrodes in a convertible form

Question 41

State where oxidation occurs during the discharging process within a secondary cell

Answer 41

Anode (negative terminal)

Question 42

State where reduction occurs during the discharging process within a secondary cell

Answer 42

Cathode (positive terminal)

Question 43

State where oxidation occurs during the recharging process within a secondary cell

Answer 43

Anode (positive terminal)

Question 44

State where reduction occurs during the recharging process within a secondary cell

Answer 44

Cathode (negative terminal)

Question 45

State the general trend that occurs when a secondary cells is recharged

Answer 45

Reactions are reversed at each electrode

Question 46

State a reason supporting the limited life of batteries

Answer 46

Unwanted physical and chemical changes that occur within them

Question 47

State what deteriorates at each charge-discharge cycle

Answer 47

Battery performance

Question 48

State what the term battery life describes

Answer 48

Number of charge-discharge cycles that occur before a battery becomes unusable

Question 49

Provide 6 factors which influence battery performance over time

Answer 49

1. Loss of active materials 2. Conversion of active material at electrodes 3. Formation of other chemicals in side reactions 4. Impurities 5. Electrolyte-electrode contact 6. Corrosion/failure of internal components

Question 50

Describe how active material may be lost to influence battery performance

Answer 50

Detachment of active material from the electrode on each cycle

Question 51

Describe active material

Answer 51

Reactants and products of the cell reaction

Question 52

Describe progressive conversion of small crystals of active material at the electrodes as a factor influencing battery performance

Answer 52

Progressive conversion of small crystals of active material at the electrodes into larger crystals at each cycle - increases resistance to current flow

Question 53

Describe formation of other chemicals in side reactions as a factor influencing battery performance

Answer 53

Formation of other chemical in side reactions - impede the efficient functioning of the cell

Question 54

Describe impurities in cell materials as a factor influencing battery performance

Answer 54

Impurities in cell materials (including electrodes) - may react with active materials

Question 55

Describe how electrolyte-electrode contact may decrease within a battery

Answer 55

Leakage of electrolyte | or transformation into non-conductive material

Question 56

Outline the relationship between battery performance and temperature

Answer 56

The higher the temperature, the higher the rate of battery deterioration

Question 57

State what batteries release under normal operation

Answer 57

Heat energy

Question 58

State what occurs when battery operating temperature rises

Answer 58

The rate of the side reactions increase and the battery life becomes shorter

Question 59

State whether lithium-ion or nickel-metal hydride batteries are more sensitive to the effect of heat

Answer 59

Nickel-metal hydride batteries

Question 60

State what occurs when batteries operate under cold conditions

Answer 60

Battery capacity decreases

Question 61

State why battery capacity decreases when batteries operate under cold conditions

Answer 61

Reactions rate fall as temp decreases | Therefore, batteries deliver less electric charge at specific discharge rates under cold conditions

Question 62

Summarise the effect of temperature on battery life/performance

Answer 62

Cold conditions - decrease battery performance | Warm conditions - decrease battery life

Question 63

State whether or not side reactions and deterioration continue even when batteries are not in use

Answer 63

Yes.

Question 64

Describe self-discharge

Answer 64

Continuation of side reactions/deterioration of battery even when not in use

Question 65

State how battery life can be extended when it is not in use

Answer 65

Storage at low temperature (which slow side reactions)