Chapter 3 - Electrochemistry

Question 1

What is a battery called ?

Answer 1

Galvanic cell and it is a type of electrochemical cell

Question 2

What does the electrochemical cell do?

Answer 2

It converts the energy released in a chemical reaction into electrical energy

Question 3

How do galvanic cells produce energy?

Answer 3

Through the transfer of electrons from 1 substance to another.

Question 4

Define half reaction.

Answer 4

Is a type of chemical equation that shows the electrons either lost, which is oxidation half reaction, or gained by the reactants, which is reduction half reaction

Question 5

On the right, the reactant has (1)… , this is…

On the left the reactant has (2)… , this is…

Answer 5

Lost electrons, oxidation

Gained electrons, reduction

Question 6

Half reaction always…1… & …2…

Answer 6

Occur in pairs and include electrons

Question 7

The reaction that takes place in Ni-Cd battery is

Answer 7

Oxidation half reaction: Cd&raquo_space; Cd2+ + 2 e-

Reduction half reaction: 2 Ni3+ + 2e- &raquo_space; 2 Ni2+

Question 8

No. Of electrons given off during (1)… is Equal the No. Of electrons gained through (2)… For the overall equation to (3)…

Write the overall Ni-Cd cell equation.

Answer 8

Oxidation
Reduction
Balance
2Ni3+ + Cd&raquo_space; 2 Ni2+ + Cd2+

Question 9

How to produce electricity & what’s like?

Answer 9

Electricity is produced due to the chemical reactions of oxidation and reduction that lead the electrons to move from 1 region to another (from the anode to cathode) because of their difference in potential energy that drive them.

The cell must be connected by an external circuit as electrodes ( that are electrical conductors and serve as a site for chemical reactions) and electrolyte ( that separates the electrodes and allows the flow of electrons released during oxidation to transfer to the reactant being reduced while following an appropriate path)

Question 10

At the anode, … takes place and is the … of electrons in the current flow.

At the cathode, … takes place and it … the electrons sent from the anode through ……. to complete the reduction.

Answer 10

Oxidation , source

Reduction, receives , external circuit

Question 11

Voltage measured across the cell by the …(1)…

Thus, the greater the ….(2)… the higher the voltage and energy associated with the electron transfer.

Answer 11

(1) Difference in electrochemical potential

(2) Difference in potential

Question 12

Explain the reaction on the Ni-Cd battery

Answer 12

The anode (-ve electrode) is made from Cd and the cathode (+ve electrode) is made from NiO(OH)
The Cd is oxidized to Cd2+ as it lost 2 e- that in turn Cd2+ combine with OH- to form Cd(OH)2
The oxidation half reaction:
Cd (s) + 2 OH (aq)&raquo_space; Cd(OH)2 + 2 e-
Cd&raquo_space; Cd2+ + 2 e-
The Ni3+ present in the form of NiO(OH) is reduced to Ni2+ in the chemical form Ni(OH)2

As the reduction half reaction:
2NiO(OH) (s) + 2H2O (l) +2e-&raquo_space; 2 Ni(OH)2 + 2OH- (aq)
2 Ni3+ + 2 e- &raquo_space; 2Ni2+

Question 13

How do rechargeable batteries work?

Answer 13

A rechargeable battery employs electrochemical reactions that can run in both directions.
The transfer of electrons takes place both during the forward (discharging) and the reverse (recharging) processes.

Cd + 2NiO(OH) + 2H2O >discharging&raquo_space; Cd(OH)2 + 2Ni(OH)2

Question 14

What may ban the battery from recharging?

Answer 14

1) the accumulation of impurities breakdown the separators

2) the generation of unwanted side-reaction by-products ends its useful life

Question 15

Most electrochemical cells convert chemical energy into electrical energy with efficiency…
While coal fired power plants generate electricity with efficiency..

Answer 15

90%

30- 40%

Question 16

The combustion products of methane are….

While that of Hydrogen is ….
Moreover, hydrogen releases more energy than methane by

Answer 16

CO2 and water
Water vapor only
3 times as the equation: H2 + 0.5 O2&raquo_space; H2O + 249 kJ

Question 17

What the side effects that may happen from using H as a fuel?

Answer 17

• Depending on the engine conditions & temperature some NO may form
• And as with flammable fuel sources as methane and gasoline,when hydrogen is directly mixed with oxygen a spark may set off an explosion, so hydrogen can be considered as an explosive fuel.

Question 18

What is the fuel cell?

Answer 18

It is an electrochemical cell that converts chemical energy into electric energy directly without burning fuel

Question 19

A US space shuttle has been fueled with … As it carried 3 sets of 32 cells. These fuel cells have powered computers, motors and lights

Answer 19

Hydrogen

Question 20

Fuel cells need… Or … To accept the … Released by the fuel.

Answer 20

1) External supply of oxygen gas or other “oxidant” material
2) Electrons that are lost by the fuel

Question 21

True or false: fossil fuels do not run down or need to be recharged in the same manner as conventional batteries do.

Answer 21

True

Question 22

True or false: chemicals being oxidized and reduced are physically separated that is they do not come in direct contact with each other ( )

Answer 22

True

Question 23

What’s the difference between the anode in the galvanic cells and in fuel cells?

Answer 23

In galvanic cells: it is the source from which the electrons are released
In fuel cells: it is just an (electric conductor) that provides a physical location in the cell at which the oxidation of the fuel takes place.

Question 24

What’s the function of cathode & electrolyte in fuel cells?

Answer 24

The cathode is an electric conductor where reduction of oxygen takes place & does not enter into the reaction itself.
The electrolyte, as in a conventional electrochemical cell, separates the anode from the cathode and allow the flow of ions and hence the flow of charge.

Question 25

What kind of electrolytes used in both galvanic cells and fuel cells?

Answer 25

Galvanic : Use very strong base KOH or NaOH

Fuel: use very strong corrosive acid, H3PO4. Thus, these fuels are closed systems that fully contained the liquid