How Does a Lead Acid Battery Work? Charging, Discharging & Reactions Explained
Lead acid battery is essential in chemistry and helps students understand various practical and theoretical applications related to this topic.
These batteries are widely used in vehicles, backup power supplies, and solar energy systems, making them a key subject in both electrochemistry and daily life.
What is Lead Acid Battery in Chemistry?
A lead acid battery refers to a rechargeable electrochemical cell that produces electricity through chemical reactions between lead plates and diluted sulfuric acid. This concept appears in chapters related to electrochemical cells, redox reactions, and battery technology, making it a foundational part of your chemistry syllabus.
Molecular Formula and Composition
- The molecular formula of the electrolyte in a lead acid battery is H2SO4 (sulfuric acid).
- A complete lead acid battery consists of lead dioxide (PbO2) as the positive plate, sponge lead (Pb) as the negative plate, and diluted sulfuric acid as the electrolyte.
- It is categorized under secondary cells, meaning it is rechargeable and can be used repeatedly.
Preparation and Synthesis Methods
- In industry, lead acid batteries are manufactured by assembling several cells, each made with grids and plates of Pb and PbO2, separated by a porous material, and then filling the cell with diluted sulfuric acid.
- In the laboratory, small cells can be prepared by placing clean strips of lead and a lead sheet oxidised to PbO2 in a sulfuric acid solution.
- Charging is done by connecting the cell to an external power source, initiating redox reactions.
Physical Properties of Lead Acid Battery
- A lead acid battery often has a rectangular or cylindrical casing.
- The typical voltage per cell is about 2.0 volts.
- The battery contains a transparent or opaque case, with visible plates and electrolyte.
- The solution is colorless initially, but the plates change color during charging and discharging.
- Lead acid batteries are heavy and have moderate energy density (about 30-50 Wh/kg). The acid is corrosive, and the battery is recyclable.
Chemical Properties and Reactions
The main chemical reactions in a lead acid battery involve redox processes.
During discharge:
At the anode (Pb): Pb(s) + SO42– → PbSO4(s) + 2e–
At the cathode (PbO2): PbO2(s) + SO42– + 4H+ + 2e– → PbSO4(s) + 2H2O(l)
Overall: Pb + PbO2 + 2H2SO4 → 2PbSO4 + 2H2O
Charging involves reversing these reactions by applying an external voltage.
Frequent Related Errors
- Confusing lead acid battery with dry cell or lithium-ion batteries.
- Forgetting that both electrodes convert to PbSO4 during discharge.
- Mislabeling the direction of electron flow or the nature of the redox reactions.
- Neglecting the role of sulfuric acid concentration during charging/discharging.
Uses of Lead Acid Battery in Real Life
Lead acid batteries are widely used to start car engines, operate backup power systems, store solar energy, power wheelchairs, and supply electricity during outages. They are common in industries and homes, providing affordable and reliable energy storage.
Relation with Other Chemistry Concepts
Lead acid batteries are closely related to galvanic cells and electrolysis, as both principles are used in discharge and charging, respectively. Their redox chemistry links them to the concept of redox reactions, and environmental discussions about their recycling relate to green chemistry.
Step-by-Step Reaction Example
1. Set up two plates, one of lead (Pb) and one of lead dioxide (PbO2), in dilute sulfuric acid.2. On discharge:
3. At the PbO2 cathode: PbO2 + SO42– + 4H+ + 2e– → PbSO4 + 2H2O
4. Combine to get the overall equation:
Lab or Experimental Tips
Always handle lead acid batteries with gloves and goggles. Avoid skin contact with sulfuric acid. Observe color changes in the plates and measure terminal voltage during charging and discharging. Vedantu educators often remind students to draw clean diagrams with labeled electrodes for full marks.
Try This Yourself
- Draw a labeled diagram of a lead acid battery and mark the positive and negative plates.
- State the changes that occur at each electrode during discharge.
- List any two everyday uses of lead acid batteries in your household or surroundings.
Final Wrap-Up
We explored lead acid battery—its structure, chemical reactions, applications, and real-life importance. Understanding its functioning helps you grasp bigger concepts in electrochemistry and sustainability. For more in-depth explanations and exam-prep tips, explore live classes and notes on Vedantu.
For related topics, check out these pages: Redox Reaction, Green Chemistry, Battery Types.
FAQs on Lead Acid Battery: Chemistry, Structure, and Function
1. What is a lead-acid battery?
A lead-acid battery is a rechargeable electrochemical cell that uses lead plates and dilute sulfuric acid to store and supply electrical energy. It is commonly used in vehicles, backup power, and solar applications due to its reliability and recyclability.
2. How does a lead-acid battery work?
A lead-acid battery works by converting chemical energy into electrical energy through redox reactions between lead, lead dioxide, and sulfuric acid. During discharging, lead is oxidized and lead dioxide is reduced, generating electricity. Charging reverses these reactions to restore the battery’s capacity.
3. What are the main components of a lead-acid battery?
The lead-acid battery consists of the following key components:
- Positive plate (lead dioxide, PbO2)
- Negative plate (spongy lead, Pb)
- Electrolyte (dilute sulfuric acid, H2SO4)
- Separator (porous insulating material)
- Battery case and terminals
4. What are the chemical reactions during charging and discharging?
During discharging:
- Negative plate: Pb + SO42- → PbSO4 + 2e-
- Positive plate: PbO2 + SO42- + 4H+ + 2e- → PbSO4 + 2H2O
5. What are the different types of lead-acid batteries?
Common types of lead-acid batteries include:
- Flooded (Wet cell)
- Valve Regulated Lead Acid (VRLA) − sealed, includes AGM and Gel types
- AGM (Absorbent Glass Mat)
- Gel battery
6. Where are lead-acid batteries commonly used?
Lead-acid batteries are widely used in:
- Automobiles (start, light, ignition)
- Uninterruptible Power Supplies (UPS)
- Solar energy storage
- Inverters and emergency lighting
7. What are the main advantages of lead-acid batteries?
Key advantages of lead-acid batteries:
- Lower cost compared to other battery types
- Reliable and robust technology
- Easy to recycle and dispose
- High surge current capability for starting engines
8. What are the disadvantages of lead-acid batteries?
Main disadvantages include:
- Heavy weight and bulky size
- Lower energy density than lithium-ion batteries
- Requires regular maintenance
- Environmental hazards if not recycled properly
9. How should lead-acid batteries be maintained and disposed?
For safe maintenance and disposal:
- Keep terminals clean and check electrolyte level regularly (flooded types)
- Avoid overcharging and deep discharging
- Recycle batteries at authorized facilities to recover lead and reduce pollution
- Handle with gloves and goggles as lead and acid are hazardous
10. What is the difference between lead-acid and lithium-ion batteries?
Lead-acid batteries are heavier, less energy-dense, and require more maintenance, but are less expensive and easier to recycle. Lithium-ion batteries offer higher energy density, lighter weight, and longer lifespan but at a higher cost and with recycling challenges.
11. What is the purpose of recycling lead-acid batteries?
Recycling lead-acid batteries reduces hazardous waste, conserves resources, and helps prevent soil and water contamination by recovering lead, plastic, and acid for reuse.
12. Why is voltage regulation important in lead-acid battery maintenance?
Voltage regulation is crucial to prevent overcharging or undercharging, which can cause reduced battery life, decreased efficiency, and safety risks. Proper voltage ensures optimal battery performance and longevity.
