Advanced Notice Artcile Predicted Questions

Question 1

Give three examples from the twelve principles of green chemistry

Answer 1

1. Better atom economy=more feedstock incorporated into products and less waste products
2. Lower energy usage=lower temperature and pressure processes
3. Use renweable feedstocks=instead of depleting natural resources

Question 2

What is a proton exchange membrane?

Answer 2

A semi-impermeable membrane designed to conduct protons whilst acting as an electronic insulator and reactant barrier

Example=to oxygen and gas

Question 3

How do proton exchange membranes make fuel cells?

Answer 3

• At the anode hydrogen ions and electrons formed by splitting a hydrogen molecule
• Hydrogen ions permeate across the electrolyte to the cathode~Electrons flow through an external circuit and produce electric power
• Oxygen in the form of air is supplied to the cathode and combines with the electrons and hydrogen ions to produce water

Question 4

What are the half equations for a fuel cell?

Answer 4

Anode=2H(2) —–>4H(+) + 4e-
Cathode=4H(+) + O(2) —–>2H(2)O

Question 5

What is the overall reaction for a fuel cell?

Answer 5

2H(2) + O(2) —->2H(2)O

Question 6

Why can carbon be used as an electrode?

Answer 6

Carbon in the form of graphite can condcut electricity as each carbon in the giant structure is covalently bonded to 3 other carbon atoms~This generates a delocalised electron per carbon which is free to move and carry a charge

Question 7

What is the oxidation state of vanadium in VO(2+) and VO2(+)?

Answer 7

• +4
• +5

Question 8

Why is vanadium considered a transition metal?

Answer 8

It has at least one stable ion with an incomplete 3d subshell

Question 9

What are the two half equations for the vanadium redox flow battery(VRFB)?

What is the overall redox equation

Answer 9

• Negative Terminal=V(2+) ——>V(3+) + e-
• Positive Terminal=VO2(+) + 2H(+) + e- —->VO(2+) + H2O
  Overall: V(2+) + VO2(+) + 2H(+) ——>V(3+) + VO(2+) + H2O

Question 10

What is the oxidation state of vanadium in V2O5?

Answer 10

+5

Question 11

What is the half equation for the reaction between vandadium peroxide in sulfuric acid?

Answer 11

V2O5 + 6H(+) + 2e- (EQUILIBRIUM ARROW) 2VO(2+) + 3H2O

Question 12

How do rechargable batteries work?

Answer 12

• External electrical charge is applied to revers the flow of lithium ions
• During charging the lithium ions move from the positive electrode to the negative electrode
• During discharging they move back in the oppsoite direction

Question 13

What is energy density and how do you calculate it?

Answer 13

Energy produce per kg of fuel burnt
Calculated by multiply the standard enthalpy of combustion by the moles in kg

Question 14

What is an electroylte?

Answer 14

The electroylte is the substance which contains free ions and carries charge

Question 15

Evaluate the use of vanadium redox flow batteries

Answer 15

• Advantages=uses less material than lithium ions + can expand energy storgae/capacity + can be scaled up to industrial level easier and cheaper
• Disadvantages=lower energy density

Question 16

Evaluate the use of lithium-ion batteries

Answer 16

• Advantages=well suited for small devices + responds quickly to changes in power demands + much higher energy density
• Disadvantages=takes a long time to charge + batteries decay over time

Question 17

How do you calculate kilowatt-hours?

Answer 17

A kilowatt-hour (kWh) is a unit of enrgy which specifically measure of the electrical energy consumed over a period of time
kWh=power(kW) x time(h)

Question 18

How do you calculate battery power density and power density?

Answer 18

• Energy=power x time
• Battery power density= energy/mass
• Power density=power/mass