📖 In-Depth Theory
Chemical Cells
A CHEMICAL CELL converts chemical energy into electrical energy through redox reactions.
A SIMPLE CELL consists of:
Two different METAL ELECTRODES (e.g. zinc and copper).
An ELECTROLYTE — a solution that conducts electricity (e.g. copper sulfate solution or sulfuric acid).
HOW IT WORKS:
The more reactive metal (e.g. zinc) acts as the NEGATIVE electrode (anode) — it loses electrons (oxidation).
The less reactive metal (e.g. copper) acts as the POSITIVE electrode (cathode) — it gains electrons (reduction).
Electrons flow through an external circuit from negative to positive electrode.
Ions carry charge through the electrolyte.
FACTORS AFFECTING VOLTAGE:
1. TYPE OF METALS — the greater the difference in reactivity, the greater the voltage produced.
2. TYPE OF ELECTROLYTE — different electrolytes give different voltages.
3. CONCENTRATION OF ELECTROLYTE — affects ion availability.
4. TEMPERATURE — affects rate of reaction and therefore voltage.
Batteries
A BATTERY consists of TWO OR MORE CELLS connected in series.
Voltage of a battery = sum of voltages of individual cells.
Two 1.5 V cells in series = 3 V battery.
NON-RECHARGEABLE BATTERIES (PRIMARY CELLS):
Chemical reactions are irreversible — the battery is used once and discarded.
Examples: alkaline batteries (AA, AAA, D), zinc-carbon batteries.
RECHARGEABLE BATTERIES (SECONDARY CELLS):
Chemical reactions are reversible — electrical energy is applied to reverse the cell reactions.
Examples: lithium-ion (phones, laptops), lead-acid (car batteries), nickel-metal hydride.
When a rechargeable battery is recharged, the external power supply REVERSES the redox reactions — restoring the original reactants.
EVENTUALLY:
Repeated charge-discharge cycles gradually degrade the electrode materials.
Batteries lose capacity over time and must eventually be replaced.
Uses and Environmental Considerations
USES OF BATTERIES:
Portable electronic devices: phones, laptops, tablets.
Electric vehicles: large lithium-ion battery packs.
Energy storage: grid-scale batteries storing renewable energy.
Medical devices: pacemakers, hearing aids.
Emergency backup power.
ENVIRONMENTAL CONSIDERATIONS:
Batteries contain toxic metals (lead, cadmium, lithium, nickel) — must be disposed of carefully.
Recycling batteries recovers valuable materials and prevents toxic waste.
Rechargeable batteries reduce waste compared to single-use.
COMPARING CELLS AND BATTERIES:
A single cell: limited voltage and capacity.
A battery: higher voltage (cells in series), more energy stored.
BATTERY CAPACITY:
Measured in milliamp-hours (mAh) or watt-hours (Wh).
Higher capacity = more energy stored = longer usage time.
⚠️ Common Mistake
A BATTERY is two or more cells connected in series — a single cell is NOT a battery. The voltage increases when cells are added in series. The greater the difference in reactivity of the two metals in a cell, the greater the voltage produced.