Heat energy

When you heat something up you are giving it heat energy. This heat energy raises the temperature of the object that you are heating and so we can say that the rise in temperature is a good guide to the amount of heat energy that we have put in – more energy the greater the rise in temperature.


If you do some simple experiments on heating things you will quickly realise that for the same amount of heat energy put in (say using a certain Bunsen burner for a certain amount of time) the rise in the temperature of different objects is different. The rise in temperature will depend on three things:
(a) the amount of heat energy that you put in
(b) the amount (mass) of the object that you are heating
(c) the material from which the object is made.

The more massive the object the more heat energy it needs to raise its temperature by a certain amount. For example it takes twice as much energy to heat 400 g of water from 20^oC to 100^oC as it does to heat 200 g of water from 20^oC to 100 ^oC.

This energy difference is most important these days when we are trying to save energy. Always only heat the water that you need otherwise you will be wasting energy. The hot water that you leave in the kettle will eventually cool down and all that heat energy will be lost to the surroundings.

Some materials take a lot of energy to raise their temperature. For example a kilogram of water takes more than ten times as much energy to raise its temperature by 1^oC than does a kilogram of copper.


Think about how that affects the material that saucepans are made from.

The difference between heat energy and temperature is very obvious if you think about a candle flame and beaker of boiling hot water. The candle flame is at a much higher temperature (about 900^oC but there is a lot more heat energy 'locked away' in the beaker of boiling hot water.

Once you have got something hot it is important to try and keep it hot. It is for this reason that insulation jackets are put round hot water tanks.

When you heat something steadily its temperature also rises steadily. However there is always going to be some heat energy lost to the room. The bigger the difference between the temperature of the object being heated and the temperature of the room the faster the object will cool.