The sequence for HEATING water is: solid – (melting) – liquid – (evaporation or boiling ) – gas
The sequence for COOLING water is: gas – (condensation) – liquid – (freezing) – solid
Temperature can be measured
EXAMPLE QUESTIONS
What happens when water is heated?
What can happen when water is cooled?
What happens when water is boiled?
What do you think steam is?
How can you measure how hot something is?
HEATING AND COOLING WATER SEQUENCES
The sequence for heating is:
ICE – melts – WATER – boils – WATER VAPOUR
The sequence for cooling is:
WATER VAPOUR – condenses –WATER – freezes – ICE
STEAM
We tend to think of steam as something that comes form a kettle full of boiling water, or from our mouths when we exhale in cold weather.
We think of steam as something we can see.
Strictly speaking though, steam is the scientific term for water vapour that is produced by boiling water.
In its pure form, water vapour, or steam is invisible.
Scientists refer to steam as water vapour that is over 100°C.
Therefore, the ‘steamy’ breath coming out of our mouths on a cold morning is not really steam at all but condensed water vapour, because it is less than 100°C.
The ‘mist’ that can be seen rising above a kettle of boiling water is steam that has cooled to just below 100°C to form tiny droplets of water.
If you look closely at a boiling kettle spout, you will see that the gas coming out is invisible close to the spout, and that the visible droplets are forming a few centimeters away from the spout.
This idea can be confusing because there is a difference between our ‘everyday’ use of the word steam and its ‘scientific’ term.
