Chapter 15: Simple Cell Flashcards
Define a simple cell.
A simple cell is a device that converts chemical energy into electrical energy (spontaneous reaction, can happen on its own)
Define electrolyte.
An electrolyte is a molten or an aqueous solution of an ionic compound which contains mobile ions and can conduct electricity. The solution must correspond with the weaker metal in the simple cell.
Define electrode
An electrode is a rod or plate that allows the conduction of electricity in an electric cell.
For simple cells, who is the anode and who is the cathode? Who gets oxidised and who gets reduced?
Anode will always be the more reactive metal → connected to positive terminal → lose electron(s), oxidised
Cathode will always be the less reactive metal → connected to negative terminal → gain electron(s), reduced
List the 3 standard observations made for simple cell.
1) Anode/ more reactive metal becomes smaller (oxidised from element to ion)
2) Electrolyte changes colour according to the reaction → solution of more reactive metal compound formed
3) Deposit of less reactive metal forms. (reduced from ion in electrolyte to form element)
Important:
1) Anode always decreases in size
2) Cathode always increases in size (ions that are reduced to form the metal are deposited at the anode)
What are fuel cells?
- Fuel cells are not energy storage cells
- A primary cell in which reactants are constantly replaced and products are continuously removed
State the reactions at the anode (-) and the cathode (+) respectively for the hydrogen-oxygen fuel cell.
1) Anode (-): Hydrogen is oxidised to water
2H2 (g) + 4OH- (aq) → 4H2O (l) + 4e-
2) Cathode (+): Oxygen is reduced to hydroxide
O2 (g) + 2H2O (l) + 4e- → 4OH- (aq)
State the overall equation for hydrogen-oxygen fuel cell.
O2 (g) + 2H2 (g) → 2H2O (l)
What is an application of hydrogen-oxygen fuel cell, and why are they used in that particular context?
Application: used in spacecraft to provide not only energy but water for the astronauts
1) Clean fuel → no pollutants involved in the reaction
2) Very efficient → ≥70% of the chemical energy converted into electricity
What are the implications regarding hydrogen-oxygen fuel cell?
1) Difficult to find a cheap source of hydrogen gas
- Obtained through the catalytic cracking of long-chained hydrocarbons, which requires lots of heat → 670° C
- Burn fuels to produce heat
OR Obtained through electrolysis of water
- Burn fuels to produce electricity
IN CONCL: essentially burning fuels to create a source of fuel. Not a completely non-polluting fuel because of these reasons.
2) Difficult to find an effective way to store the gas
- Very big volume
- Must be stored under high pressure
State the relationship between the difference in reactivity of two metal electrodes in a simple cell and the resulting voltage.
The larger the difference in metal reactivity of the two metals, the larger the voltage.
State the relationship between the direction of electron flow between the electrodes in a simple cell and the sign of the resulting voltage.
In a simple cell, the flow of electrons is always from the more reactive metal to the less reactive metal. The sign of the resulting voltage (either +ve or -ve) only tells you the direction of flow of electrons.
In questions, they will give you different pairs of metal electrodes with varying resulting voltages that have different signs. It is up to you to infer which metal is more reactive if there is an unknown metal whose identity you must deduce.
