Comparing cells
Reaction in which energy is given out to the surroundings. The surroundings then have more energy than they started with so the temperature increases. reactions transfer The capacity of a system to do work or the quantity required for mechanical work to take place. Measured in joules (J). For example, a man transfers 100 J of energy when moving a wheelbarrow. to their surroundings. This is usually transferred by heating, but the energy can be transferred in other ways. Chemical A store of internal energy that can be transferred as an electric current in a circuit. use chemical reactions to transfer energy by The flow of charge through a conductor..
Chemical cells
Chemical cells include the familiar A chemical supply of electrical energy. For example, common battery voltages include 1.5 V and 9 V. used in torches and mobile phones. There are different designs of chemical cells, with different reactions depending on the type of cell.
Chemical cells produce a The potential difference (or voltage) of a supply is a measure of the energy given to the charge carriers in a circuit. Units = volts (V). This is the voltage between two points that makes an electric current flow between them. until one of the A substance that reacts together with another substance to form products during a chemical reaction. is used up. When this happens, we say the battery 'goes flat'.
The different materials used also change the power of the cell. For example:
- the first cells were made from zinc and copper and produced 1.1 V
- standard zinc carbon batteries used in torches or calculators produce 1.5 V
- lithium batteries in mobile phones can produce up to 3.6 V
Fuel cells
Device that produces a voltage continuously when supplied with a fuel and oxygen. work in a different way to chemical cells. Fuel cells produce a voltage continuously, as long as they are supplied with:
- a Material that is used to produce heat, like coal, oil or gas.
- oxygen (from the air)
Hydrogen-oxygen fuel cells
In a hydrogen-oxygen fuel cell, hydrogen and oxygen are used to produce a voltage. Water is the only product. The overall reaction in a hydrogen-oxygen fuel cell is:
Hydrogen + oxygen 鈫 water
2H2(g) + O2(g) 鈫 2H2O(l)
Each hydrogen-oxygen fuel cell typically produces less than 1 V, but the cells can be made very small so a battery of cells can produce a higher voltage. The fuel cell will continue to operate as long as it is provided with hydrogen (the fuel) and oxygen.