Chapter 3 - Electrochemistry Flashcards
What is a battery called ?
Galvanic cell and it is a type of electrochemical cell
What does the electrochemical cell do?
It converts the energy released in a chemical reaction into electrical energy
How do galvanic cells produce energy?
Through the transfer of electrons from 1 substance to another.
Define half reaction.
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
On the right, the reactant has (1)… , this is…
On the left the reactant has (2)… , this is…
Lost electrons, oxidation
Gained electrons, reduction
Half reaction always…1… & …2…
Occur in pairs and include electrons
The reaction that takes place in Ni-Cd battery is
Oxidation half reaction: Cd»_space; Cd2+ + 2 e-
Reduction half reaction: 2 Ni3+ + 2e- »_space; 2 Ni2+
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.
Oxidation
Reduction
Balance
2Ni3+ + Cd»_space; 2 Ni2+ + Cd2+
How to produce electricity & what’s like?
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)
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.
Oxidation , source
Reduction, receives , external circuit
Voltage measured across the cell by the …(1)…
Thus, the greater the ….(2)… the higher the voltage and energy associated with the electron transfer.
(1) Difference in electrochemical potential
(2) Difference in potential
Explain the reaction on the Ni-Cd battery
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)»_space; Cd(OH)2 + 2 e-
Cd»_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-»_space; 2 Ni(OH)2 + 2OH- (aq)
2 Ni3+ + 2 e- »_space; 2Ni2+
How do rechargeable batteries work?
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»_space; Cd(OH)2 + 2Ni(OH)2
What may ban the battery from recharging?
1) the accumulation of impurities breakdown the separators
2) the generation of unwanted side-reaction by-products ends its useful life
Most electrochemical cells convert chemical energy into electrical energy with efficiency…
While coal fired power plants generate electricity with efficiency..
90%
30- 40%
The combustion products of methane are….
While that of Hydrogen is ….
Moreover, hydrogen releases more energy than methane by
CO2 and water
Water vapor only
3 times as the equation: H2 + 0.5 O2»_space; H2O + 249 kJ
What the side effects that may happen from using H as a fuel?
- 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.
What is the fuel cell?
It is an electrochemical cell that converts chemical energy into electric energy directly without burning fuel
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
Hydrogen
Fuel cells need… Or … To accept the … Released by the fuel.
1) External supply of oxygen gas or other “oxidant” material
2) Electrons that are lost by the fuel
True or false: fossil fuels do not run down or need to be recharged in the same manner as conventional batteries do.
True
True or false: chemicals being oxidized and reduced are physically separated that is they do not come in direct contact with each other ( )
True
What’s the difference between the anode in the galvanic cells and in fuel cells?
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.
What’s the function of cathode & electrolyte in fuel cells?
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.
