L3 - Energy in Changes of State

objectives

„Water can be a solid (ice), a liquid (water), and a gas (water vapour or steam). Its state can be changed by heating or cooling:

Changing States of Water

„And when steam is cooled, the opposite changes take place:

„You can see that:

• condensing is the opposite of evaporating
• freezing is the opposite of melting
• the freezing point of water is the same as the melting point of ice, 0 °C.

All other matter can also change State - it's not just water!

„It’s not just water! Nearly all substances can exist as solid, liquid and gas. Even iron and diamond can melt and boil! Some melting and boiling points are given below. Look how different they are:

Changing States and Graphs

„Look at this graph. It shows how the temperature changes as a block of ice is steadily heated. First the ice melts to water. Then the water gets warmer and warmer, and eventually turns to steam:

A graph like this is called a heating curve.

„Look at the step where the ice is melting. Once melting starts, the temperature stays at 0 °C until all the ice has melted. When the water starts to boil, the temperature stays at 100 °C until all the water has turned to steam. So the melting and boiling points are clear and sharp.