Energy and temperature
temperatureHow warm or cold something is. is a measure of the average kinetic energyEnergy which an object possesses by being in motion. of the particleA general term for a small piece of matter. For example, protons, neutrons, electrons, atoms, ions or molecules. in a substance. It shows how hot something is, and is measured with a thermometer or a temperature sensor. There are two commonly used temperature scales:
- degrees Celsius (掳C)
- kelvin (K)
The difference between 1掳C and 2掳C is the same as the difference between 1 K and 2 K.
Temperature does not show the energyThe capacity for doing work. store associated with an object.
How do energy and temperature differ?
The energy stored in a substance or system is measured in joules (J). When energy is transferred by heating, it can:
- change the energy stored in the system
- change the physical state of the system
- make chemical reactions occur
When energy is transferred to water in the liquid state, water moleculeA collection of two or more atoms held together by chemical bonds. gain kinetic energy and speed up. The larger the mass of water, the more energy needed to raise the temperature by a given amount. This is because more molecules need to have their speed changed.
Example
In the diagram above, the water in the two beakers has been heated by the same Bunsen burner for the same amount of time. This means that the same amount of energy is transferred to both. However, the smaller volume of water increases in temperature more. The same amount of energy has been transferred to a smaller number of particles, so on average each one moves faster than the particles in the other beaker.
Imagine a teaspoon of boiling water at 100掳C and a large bowl of water at room temperature (about 20掳C):
- the teaspoon of water could not melt an ice cube - even though each particle has a greater energy store because there are relatively few of them
- the bowl of water could melt an ice cube - even though on average each particle has a smaller energy store because there are many more of them, so the total energy available for transfer is much greater