Electrochemical

Question 1

Define Oxidation

Answer 1

loss of electrons at the anode and increase in oxidation number

Question 2

Define Reduction

Answer 2

gain of electrons at cathode and decrease in oxidation number

Question 3

What is a Direct reaction?

Answer 3

a spontaneous reaction that doesn’t require an external source of energy

Question 4

What is an Indirect reaction?

Answer 4

2 different solutions are separate as have external energy source

Question 5

Limitations of electrochemical series

Answer 5

• only have voltages at SLC
• doesn’t state the rate of reactions when 2
  substances mix
• concentrations have to 1M; doesn’t have any others

Question 6

How do you do KOHES in a BASIC solution?

Answer 6

KOHES + 2 steps (1 is add OH- to both sides & 2 is cancel everything else out after H+ and OH- join to form water)

Question 7

What is a primary cell?

Answer 7

• It cannot be recharged
• The amount of energy supplied is limited to the amount of reactants available within cell

Question 8

What is a secondary cell?

Answer 8

• It can be recharged
• The reactants used to power devices can be reformed from the products of the discharge reactions

Question 9

What are some factors impacting cell selection? (7)

Answer 9

• Initial & operating costs
• Size and shape
• Mass
• Memory affect
• Voltage
• Current
• Shelf life

Question 10

What are fuel cells?**

Answer 10

A type of galvanic cell that has fuel consistently pumped in and electricity is continuously generated

*note: fuel is ALWAYS at anode & oxygen ALWAYS at cathode

Question 11

What is an electrolyte?

Answer 11

• A solution that conducts electricity due to ions being able to flow past each other.
• May be a molten ionic compound or a dissolved ionic compound.

Question 12

Why do fuel cells use porous electrodes?

Answer 12

• the electrodes are made from material with many holes (pores)
• this allows a GREATER surface area for reaction to take place thus a GREATER rate of reaction
• also allows reacting gases to access electrolyte.

Question 13

What are some advantages of a fuel cell with hydrogen as the fuel?

Answer 13

• lower emissions of harmful sulfur/nitrogen containing compounds
• low maintenance and running costs
• QUIET
• No direct CO2 emissions
• Greater efficiency than direct combustion

Question 14

What are some disadvantages of a fuel cell with hydrogen as the fuel?

Answer 14

• Storage and safety issues with highly explosive hydrogen fuel
• Expensive to manufacture (especially porous electrodes)
• Requires new infrastructure for hydrogen fuels (eg. fuel stations)
• Potentially still not as efficient or convenient as batteries

Question 15

Compare Fuels cells and Combustion reactions

Answer 15

• Fuel cells have a higher energy efficiency whereas combustion reactions have a lower energy efficiency
• Fuel cells are (generally) more expensive whereas combustion reactions are cheaper
• Fuel Cells pollutants depend on fuel used whereas combustion reactions pollutants can include CO2, CO or NO2
• Fuel cell have one energy transformation (chemical-> electrical) whereas combustion reactions have many many energy transformations
• Fuels cells are quieter whereas combustion reactions are nosier

Question 16

What are some disadvantages for using hydrogen fuel?

Answer 16

• Hydrogen is highly flammable and can be explosive = dangerous
• Hydrogen is odourless, tasteless and colourless = difficult to detect leaks
• Very difficult to safely store
• Flames of burning hydrogen are almost invisible = difficult for fire fighters

Question 17

What is Faraday’s First law?

Answer 17

The quantity of electric charge (i.e Q in coulombs) carried by a given galvanic cell is directly proportional to the mass lost from the anode or gained at the cathode

Question 18

*What is Faraday’s Second law?

Answer 18

• For a given starting amount of anode, the number of mols of electrons produced by a galvanic cell is directly proportional to the coefficient of electrons in the balanced oxidation half-equation
  e.g: start 1 mol Ag atoms at anode
  Ag-> Ag+ + e-
  coefficient of e- is 1 thus 1 mol

Question 19

What is Faraday’s constant?

Answer 19

96500 C

Question 20

What is Avogadro’s constant?

Answer 20

6.02 x 1023 mol-1

Question 21

In galvanic cells, what are the charges of the electrodes?

Answer 21

Anode = negative
Cathode = positive

Question 22

In electrolysis, what are the charges of the electrodes?

Answer 22

Anode = positive
Cathode = negative

Question 23

What is an electrolytic cell?

Answer 23

• A cell that uses an electric current (DC) to force a chemical reaction to occur that would otherwise not happen.
• Composed of two electrodes in an electrolyte that is commonly an aqueous solution or molten ionic compound.

Question 24

What is special about using molten substance and not aqueous?

Answer 24

NO WATER IS INVOLVED

Question 25

What is the energy shift in discharge and in recharge for a secondary cell?

Answer 25

• Discharge (galvanic) = chemical energy -> electrical energy
• Recharge (electrolysis) = electrical energy->
  chemical energy

Question 26

What conditions must be present in order for a secondary cell to be recharged?

Answer 26

• Products of discharge must stay in contact with electrodes
• Voltage is higher than the voltage produced when discharging in order to fully recharge
• positive terminal of power supply connected to positive terminal of cell and same for negative terminals

Question 27

For discharge and recharge, what are the charges of the anode and cathode?

Answer 27

• Discharge = anode: negative & cathode: positive
• Recharge = anode: positive & cathode: negative

Question 28

What are some common secondary cells?

Answer 28

• Lead-Acid battery
• Nickel-Metal Hydride