20.2_Batteries_Final_Version_with_questions_and_answers (1)
20: Electrochemistry - Section 2: Batteries
1. Structure and Operation of Batteries
Battery definition: They are voltaic cells that use spontaneous rxns to provide energy for a variety of purposes.
Components Common in Batteries:
Electrolytes:
Serve as medium for ion migration
Different compositions for different battery types
Anode and Cathode:
Anode: Site of oxidation (loss of electrons)
Cathode: Site of reduction (gain of electrons)
2. Types of Batteries
1)Primary Batteries (non-rechargeable)(1use only)
produces electric energy using redox rxns that r not easily reversed.
irreversible redox rxn
Dry cell: an electrochemical cell in which the electrolyte is a moist paste.
paste: is a moist substance typically produced by mixing dry ingredients with a liquid.
function of electrolyte in the paste is to help ions move or migrate between electrodes( anodes and cathodes)
3 main examples are:
Zinc-carbon battery:
Anode: Zinc shell : Zn(s)—> Zn^2+(aq) + 2e^-
Cathode: Carbon rod (inactive cathode, does not participate) purpose is to conduct electricity
half redox rxn takes place in the paste
Voltage: 1.5V
Paste is inside the zinc case
Contains a moist paste made of zinc chloride, manganese(IV) oxide(MnO2), ammonium chloride(NH4Cl), a small amount of water
Zinc casing acts as anode, carbon rod as cathode
Alkaline battery:
Uses potassium hydroxide (KOH) as electrolyte
uses basic KOH paste
More efficient than zinc-carbon, it doesn’t need carbon rod cathode so it can be made small and more useful for smaller devices
anode: Zn-KOH
zn in this case is powdered form so it increases the surface are for rxn
anode(oxidation) half cell rxn: Zn+ 2OH→ ZnO +H20 +2e^-
cathode: Mn02 -KOH
cathode(reduction) half cell rxn: MnO2+2H20 +2e → Mn(OH)2 + 2OH-
Silver battery:
Used in small devices (hearing aids, watches, and cameras)
anode: Zn-KOH SAME ANODE HALD RXN AS ALKALINE BATTERY
cathode: Ag20, cathode half rxn: Ag20 +H2O+ 2e- → 2Ag+ 2OH-
smallest primary battery
Smaller and lighter than alkaline batteries
2)Secondary Batteries (rechargeable)
reversible redox rxns.
called storage batteries because the chemical potential energy is being stored.
Lead-acid battery:
Common in cars (AUTOMOBILES)
Electrolyte: Sulfuric acid
it’s called lead Acid storage because its a solution of sulfuric acid.
it uses sulfuric acid as an electrolyte instead of water because sulphuric acid is two times denser than water which affects batteries
: high energy density stores lot of energy and will keep ur phone charged for longer than a lower energy density (high density -high storage)
Total voltage: 12V
(6 cells and each produces 2 so 6×2)
Nickel-Cadmium (NiCad) battery:
Electrolyte: Typically, a potassium hydroxide (KOH) solution is used, which allows for efficient ion transfer during the redox reactions.
Used in cordless tools and devices (drills, screwdrivers, shavers, and camcorders , phones)
anode: cadmium:
Cd+ 2OH- → Cd(OH)2 +2e-
cathode: Nickle oxide:
NiO(OH) + H20+e- → Ni(OH)2 + OH-
When the battery is recharged, these reactions are reversed.
OVERALL RXN: 2NiOOH + Cd + 2H20 →←2NI(OH)2+Cd(OH)2
nonspontaneous recharge reaction.
Q!!!) HOW DO SECONDARY AND PRIMARY BATTERIES DIFFER?:
Primary batteries are thrown away(non rechargeable) and the rxn is not easily reversed, while secondary batteries are rechargeable and the redox rxn is reversible.
Type 1 and 2: Lithium Batteries
3)Fuel Cells (continuous supply)
IMP DIFF : FUEL CELLS R NEVER DEPLETED AS LONG AS THEYRE PROVIDED WITH A STEADY SOURCE OF FUEL.
Hydrogen fuel cell:
Electric energy produced by redox reactions
Oxidation of hydrogen and reduction of oxygen
Anode: hydrogen
catode: oxygen
2H2 + O2 → 2H2O + energy
Methane fuel cell:
Uses methane as fuel
anode: methane
cathode: oxygen
not useful cuz it releases carbon dioxide into the air as exhaust gas.
Proton-exchange membrane (PEM) fuel cell:
Uses a plastic sheet(proton exchange membrane PEM) as an electrolyte, which eliminates the need for a liquid electrolyte
anode: hydrogen
cathode:oxygen
The by-product of this redox reaction is water.
A "stack" of PEM-type cells can generate enough energy to power an electric car.
List two ways in which a fuel cell differs from an ordinary battery.
In a fuel cell, fuel is oxidized to produce electricity. Batteries must be recharged or replaced. Current can be produced and sustained in a fuel cell if a fuel source is present.
Fuel Cells Explain how the oxidation of hydrogen in a fuel cell differs from the oxidation of hydrogen when it burns in air.
In a fuel cell, hydrogen oxidation is controlled so that most chemical energy is converted to electrical energy instead of heat.
3. Principles of Fuel Cells
Operate using an external fuel source
Can produce electrical energy as long as the fuel is available
Controlled oxidation of hydrogen produces water as a by-product
4. Corrosion: Definition and Prevention
Corrosion:
Loss of metal due to oxidation-reduction reactions of metal with the environment
Commonly observed in iron as rusting (4Fe + 3O2 = 2Fe2O3)
anode: iron
cathode: water
Methods to Prevent Corrosion:
Painting or Coating: Seals out air and moisture
Sacrificial Anodes: Use more reactive metals (magnesium or aluminum) that oxidize instead of iron
Galvanization: Coating iron with zinc to prevent rusting, protecting the iron from moisture and air
5. Summary of Battery Properties
Key Properties of Batteries:
Convert chemical energy into electrical energy
Use electrochemical cells which consist of one or more voltaic cells
Dependent on redox reactions that are either spontaneous or reversible depending on the battery type
Three main types: primary, secondary, and fuel cells
6. Key Questions to Consider
What are the structural differences between primary and secondary batteries?
How does a fuel cell differ operationally from an ordinary battery?
What role does corrosion play in metal deterioration, and how can it be prevented effectively?