Memory Anchor:

• Super Challenge:

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  Challenge:

Key Questions:

1. Why are chemical cells useful?
   • Cells contain chemicals which react to produce electricity.
2. What factors can affect the voltage produced by a chemical cell?
   • The voltage produced by a Cell is dependent upon a number of factors including the type of electrode and electrolyte.
3. How can a simple chemical cell be made?
   • A simple Cell can be made by connecting two different metals in contact with an electrolyte.
4. What is the structure of a battery like?
   • Batteries consist of two or more Cells connected together in series to provide a greater voltage
5. Why do re-chargeable cells and batteries stop working?
   • In non-rechargeable Cells and batteries the chemical reactions stop when one of the reactants has been used up.
6. How can re-chargeable cells and batteries be re-charged?
   • Rechargeable Cells and batteries can be recharged because the chemical reactions are reversed when an external electrical current is supplied.
7. Which cell would be the best choice to use to power a machine? Cell A produces 0.01V of energy and cell B produces 0.20V of energy. Give a reason for your answer.
   • Cell B would be the better choice to power a machine as it produces more electricity.
8. What type of batteries are non-rechargeable?
   • Alkaline batteries are non-rechargable.
9. How do fuel cells produce a potential difference?
   • Fuel Cells are supplied by an external source of fuel (eg hydrogen) and oxygen or air. The fuel is oxidised electrochemically within the fuel Cell to produce a potential difference.
10. What sort of reaction occurs in a hydrogen fuel cell?
    • The overall reaction in a hydrogen fuel Cell involves the oxidation of hydrogen to produce water.
11. What do hydrogen fuel cells offer alternatives to?
    • Hydrogen fuel Cells offer a potential alternative to rechargeable Cells and batteries.
12. What are the advantages and disadvantages of using hydrogen fuel cells compared with rechargeable cells and batteries?
    • Similarities: Both convert chemical Energy directly into electrical Energy using ?spontaneous? redox reactions / Both function in similar ways ? that is, there is a negative electrode where an oxidation half-reaction occurs and a positive electrode where a reduction half-reaction occurs / Both generate electrical Energy using chemical Energy (compounds in the Cells undergo chemical reactions which send electrons into an external circuit) / Both generate a current through an external circuit, which is caused by the separation of the half-reactions part of a full redox reaction / Both are made up of an electrolyte, an anode, and a cathode. Differences: The hydrogen oxygen fuel Cell is an Energy conversion device while the rechargeable battery is an Energy storage device / Fuel Cells can only provide electrical Energy when reactants (fuel) are constantly provided to the Cell (open system) / Rechargeable batteries have chemical Energy stored in its parts, in a closed system, and so can provide electricity until its stored chemical Energy is used up, at which point the battery requires recharging to renew its chemical Energy level. Fuel Cells do not require charging, as long as reactants continue to be provided, whereas rechargeable batteries must be charged, which takes the battery out of operation for a period of time / Fuel Cells can provide electrical Energy for a much longer duration, whereas rechargeable batteries can only provide Energy in an intermittent schedule / Electrodes in fuel Cells are made of porous material, which allows for the free movement of hydrogen, oxygen, and water, while those in rechargeable batteries are made of solid metal compounds and lattices / Currently, fuel Cells are much more expensive than rechargeable batteries, due to the high prices of its individual parts, such as the platinum catalysts / Currently, fuel Cells are far larger than rechargeable batteries / Fuel Cells are able to generate a large amount of electrical Energy, much greater than that produced by rechargeable batteries.
13. (HT only) What are the half equations for the electrode reactions in a hydrogen fuel cell?
    • (HT only) At the cathode (negative electrode): H2(g) – 2e– → 2H (aq) At the anode (positive electrode): 4H (aq) O2(g) 4e– → 2H2O(g)