Method
- Place some ice in a beaker
- Measure the temperature of the ice and record it.
- After 10 s measure the temperature again and record it. Repeat every 10 s, until at least 1 minute after the ice has melted.
- Heat some water in a beaker until it boils. Measure and record the temperature of the water.
- Remove the water from the heat and measure the temperature every 10 s, until the beaker is cool to touch
Be careful when handling the beaker of hot water. Do not touch the beaker with your hands, you will burn yourself.
Results
Record your results in the following table:
|
Temperature of ice |
Time (s) |
Temperature of water |
Time (s) |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Table of results
Plot a graph of temperature against time for the ice melting and the boiling water cooling.
Discussion and conclusion
Discuss your results with others in your class. What conclusions can you draw? You should find that the temperature of the ice increases until the first drops of liquid appear and then the temperature remains the same, until all the ice is melted. You should also find that when you cool water down from boiling, the temperature remains constant for a while, then starts decreasing.
In the above experiment, you investigated the heating and cooling curves of water. We can draw heating and cooling curves for any substance. A heating curve of a substance gives the changes in temperature as we move from a solid to a liquid to a gas. A cooling curve gives the changes in temperature as we move from gas to liquid to solid. An important observation is that as a substance melts or boils, the temperature remains constant until the substance has changed state. This is because all the heat energy goes into breaking or forming the forces between the molecules.
The above experiment is one way of demonstrating the changes of state of a substance. Ice melting or water boiling should be very familiar to you.
The kinetic theory of matter
The
kinetic theory of
matter helps us to explain why matter exists in different
phases (i.e. solid, liquid and gas), and how matter
can change from one phase to the next. The kinetic theory of matter also helpsus to understand other properties of matter. It is important to realise that
what we will go on to describe is only a
theory . It cannot be proved beyond doubt, but the
fact that it helps us to explain our observations of changes in phase, and otherproperties of matter, suggests that it probably is more than just a theory.
Broadly, the Kinetic Theory of Matter says that:
- Matter is made up of
particles that are constantly moving.
- All particles have
energy , but the energy varies depending on whether the
substance is a solid, liquid or gas. Solid particles have the least amount ofenergy and gas particles have the greatest amount of energy.
- The
temperature of a
substance is a measure of the
average kinetic
energy of the particles.
- A change in
phase may occur when the energy of the particles is changed.
- There are
spaces between the particles of matter.
- There are
attractive
forces between particles and these become stronger as the particles
move closer together. These attractive forces will either be intramolecularforces (if the particles are atoms) or intermolecular forces (if the particles
are molecules). When the particles are extremely close, repulsive forces startto act.
