How chemical cells produce a voltage, the difference between rechargeable and non-rechargeable, and how a hydrogen fuel cell compares with a rechargeable battery. Chemistry only content.
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1.What is a chemical cell?
A device that uses a chemical reaction to produce a voltage between two electrodes.
2.What is needed to make a simple cell?
Two different metals as electrodes, dipped into an electrolyte and connected by a wire.
3.What determines the voltage of a cell?
The difference in reactivity between the two metals, and the electrolyte used.
4.How could you make a cell produce a larger voltage?
Use two metals that are further apart in the reactivity series.
5.What is a battery?
Two or more cells connected together in series.
6.Why does connecting cells in series increase the voltage?
The voltages of the individual cells add together.
7.Why do non-rechargeable batteries stop working?
The reactions are not reversible, so once one of the reactants is used up no more voltage can be produced.
8.Give an example of a non-rechargeable cell.
An alkaline battery.
9.How does a rechargeable battery work?
The reactions can be reversed by supplying an external electric current, which restores the original reactants.
10.What is a fuel cell?
A cell supplied with a fuel and oxygen, which produces a voltage continuously while the fuel is supplied.
11.What fuel is used in the fuel cell on the specification?
Hydrogen.
12.What is the overall reaction in a hydrogen fuel cell?
Hydrogen + oxygen gives water, and the reaction is exothermic.
13.Write the overall equation for a hydrogen fuel cell.
2H2 + O2 gives 2H2O
14.What is oxidised in a hydrogen fuel cell?
The hydrogen, because it loses electrons.
15.Give three advantages of hydrogen fuel cells over rechargeable batteries.
The only product is water so there is no pollution at the point of use, they do not need recharging or lose charge over time, and they can be made in a wide range of sizes.
16.Give three disadvantages of hydrogen fuel cells.
Hydrogen is a gas so it is difficult to store and transport, it is highly flammable, and producing the hydrogen in the first place often uses fossil fuels.
17.Why is the water product an advantage?
It is not a pollutant, unlike the carbon dioxide and other gases produced by burning fossil fuels.
18.Why is hydrogen production a problem for the environmental case?
Most hydrogen is currently made from fossil fuels or by electrolysis using electricity that may come from fossil fuels, so emissions are moved elsewhere rather than removed.
19.Give an advantage of rechargeable batteries over fuel cells.
They can be recharged from mains electricity and do not need a supply of fuel to be stored or transported.
20.Give a disadvantage of rechargeable batteries.
They lose capacity over time and eventually need replacing, and their disposal creates waste.
21.What happens to the mass of the more reactive electrode in a simple cell?
It decreases, because it is oxidised and dissolves into the electrolyte.
22.Why must an electrolyte be present in a cell?
It allows ions to move and complete the circuit between the electrodes.
23.Why does a cell made from two identical metals produce no voltage?
There is no difference in reactivity between the electrodes, so there is nothing to drive electrons from one to the other.
24.Where might hydrogen fuel cells be used?
In vehicles, and in situations such as spacecraft where a reliable supply with no polluting exhaust is important.
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