M3.5 Flashcards
(35 cards)
What is the difference between a primary and secondary cell?
Primary cells are not rechargeable, secondary cells are rechargeable.
Are the electrochemical processes in a primary cell reversible?
No (they are not rechargeable)
What are dry cells?
Cell in which the electrolyte is as paste rather than a liquid.
Name 2 types of primary cell
Zinc-carbon dry cell, Alkaline battery.
What makes up a zinc-carbon dry cell?
The zinc makes up the container and acts as the negative electrode. The positive electrode is a carbon rod in the centre of the cell. It is surrounded by an electrolyte paste containing manganese oxide, zinc chloride, ammonium chloride, carbon powder and a small amount of water.
What is the nominal voltage of a zinc carbon cell and does it change during discharge?
1.5V and decreases during discharge
What is a disadvantage of a zinc-carbon dry cell?
The zinc container oxidises over time until its contents start leaking.
How do alkaline primary batteries differ from a zinc-carbon cell?
They can deliver 5 times the energy compared to similar size zinc-carbon battery. They can also be recharged a few times but are not designed to do so.
How are alkaline primary batteries similar to zinc-carbon cells?
They are also prone to leaking, so should be removed for long term storage.
Are the electrochemical reactions in secondary cells reversible?
Yes (rechargeable)
What are secondary cells used in?
Aircraft, cars, laptops etc
Name 2 examples of secondary cells
Lead Acid Cells, Nickel Cadmium Cells
What is the initial voltage and final voltage of a lead acid cell?
2.2V, discharging to 1.83V
What is a lead acid cell made of?
A lead peroxide positive plate, and a negative plate filled with pure spongy lead, with a liquid electrolyte made up of sulphuric acid(30%) and distilled water (70%).
What is the initial and discharged voltage of a nickel cadmium cell?
1.2V initial, falling to 1.0V when discharged.
What is a nickel cadmium cell made from?
The positive plate is made from nickel oxyhydroxide, the negative plate is metallic cadmium. The electrolyte is potassium hydroxide.
What will happen to the electrolyte level during charging in a nickel cadmium cell?
It will increase.
What are the advantages of Nickel Cadmium compared to Lead Acid cells?
- Tolerates higher discharge currents
- Closed circuit voltage remains almost constant throughout the discharge
- Higher energy density
- Greater number of charge/discharge cycles
What are the disadvantages of Nickel Cadmium compared to Lead Acid cells?
- More costly
- More complicated charging requirements
- Rick of thermal runaway. As battery temp rises internal resistance decreases.
- High toxicity of cadmium
What is the general structure of a galvanic cell?
A positive and negative plate with an electrolyte in the middle, surrounded by a steel plate.
What is the rated voltage of a mercury oxide coin cell?
1.35V
How does the resistance and voltage change in a mercury oxide coin cell during the discharge process?
They are constant
What arecoin cells used in?
Hearing aids, watches, meters, exposure meters and cameras
What is the rated voltage of a silver oxide coin cell?
1.55V
