Electricity from chemical reactions
Chemical cells
Chemical A store of internal energy that can be transferred as an electric current in a circuit. 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. or The potential difference across a cell, electrical supply or electrical component. It is measured in volts (V). until the Substances present at the start of a chemical reaction. are used up. When this happens, we say the battery 'goes flat'.
Fuel cells
Device that produces a voltage continuously when supplied with a fuel and oxygen. work in a different way than chemical cells. Fuel cells produce a potential difference 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
Hydrogen fuel cells may be used as an alternative to Natural, finite fuel formed from the remains of living organisms, eg oil, coal and natural gas.. The use of more hydrogen fuel cell vehicles could help to reduce the Substances that are given off, especially in the form of gas. of air A toxic chemical or object that causes damage to the land, air or water..
In a hydrogen-oxygen fuel cell, hydrogen and oxygen are used to produce a potential difference.
The overall reaction inside the cell is equivalent to the The process of burning by heat. of hydrogen. The same A substance formed in a chemical reaction., water, is formed. This means that a hydrogen fuel cell car produces no air pollutants.
The overall reaction in a hydrogen-oxygen fuel cell is:
hydrogen + oxygen → water
2H2(g) + O2(g) → 2H2O(l)
In a hydrogen fuel cell car the energy produced drives an electric motor rather than an internal combustion engine (a normal car engine).
The hydrogen fuel is usually produced by The decomposition (breakdown) of a compound using an electric current.. During the generation of the electricity (in a fossil fuel power station) air pollutants will be produced. Although no pollutants are released by the vehicle they may be emitted elsewhere.
More guides on this topic
- Formulae and equations - Cambridge OCR 21st Century
- Earth's atmosphere
- Changes of state: interactive activity - Cambridge OCR 21st Century
- Energy changes in chemical reactions
- The evidence for climate change
- Improving the supply of potable water
- Sample exam questions - air and water - Cambridge OCR 21st Century
