Energy and temperature

Internal energy is linked to the temperature of matter but the two are very different things:

  • Internal energy is a measure of the total energy of all the particles in the object or substance. This includes the kinetic energy of the particles and chemical potential energy of the bonds between them.
  • Temperature is a measure of the average speed of the particles. This is based on the kinetic energy of individual particles.

Heating water causes the water molecules to gain kinetic energy and speed up. It takes more energy to raise the temperature of a large amount of water because more molecules need to have their speed changed.

One large beaker and one small beaker filled with water, being heated by bunsen burners. The smaller beaker of water is bubbling and turning into steam.

In the diagrams above the two beakers have been heated by the same Bunsen burner for the same amount of time, so both have been given the same amount of energy. However, the smaller beaker has had a bigger temperature rise because the same energy has been given to a smaller number of particles so each particle is moving faster than those in the other beaker.

Example

Imagine a teaspoon of boiling water at 100 degrees Celsius (°C) and a large bowl of water at room temperature:

  • the teaspoon of hot water would not be able to melt an ice cube - even though the particles have lots of kinetic energy, there are very few of them
  • the bowl of room temperature water would be able to melt an ice cube - even though each individual particle has less kinetic energy, there are many more of them, making the total available energy much larger