http://www.ck12.org Chapter 2. Matter and Change
freezing (liquid to solid), and condensation (gas to liquid). Dissolving is also a reversible physical change. When
salt is dissolved in water, the salt is said to have entered the aqueous state. Boiling off the water will cause the salt
to reform in its solid state.
An example of an irreversible physical change would be grinding a piece of wood into sawdust. Such a change is
irreversible because the sawdust cannot be reconstituted into the same piece of wood that it was before. Cutting the
grass or pulverizing a rock would be other irreversible physical changes.
Some other examples of physical changes can be seen on the web:
- The melting and freezing oftert-butanol can be viewed at these two links:
- Melting: http://www.dlt.ncssm.edu/core/Chapter2-Phys_and_Chem_Prop/melt_tbutanol-lg.htm
- Freezing: http://www.youtube.com/watch?v=lQnrRIDpPlU
- Iodine undergoes an interesting physical change called sublimation. Click http://www.youtube.com/watch?v=4E0s
y-FN2M8 to watch! - Metals expand when heated. This physical change can be seen using a ball and ring at http://www.youtube.com/
watch?v=QNoE5IoRheQ.
Lesson Summary
- A pure substance is a sample of matter with a fixed composition and identifiable physical properties that are
the same for every sample of a particular substance. - Extensive properties depend on the size of a sample, while intensive properties do not.
- Solid, liquid, and gas are the three common states of matter.
- Physical changes do not alter the identity of a substance.
Lesson Review Questions
Reviewing Concepts
- Explain why water is considered a pure substance, while milk is not.
- List at least three physical properties of silver.
- Give an example of an extensive property and an intensive property of an iron nail. Explain.
- Compare the arrangements of particles in the three states of matter.
- The odor of gasoline is very strong and distinctive. Can gasoline in the gaseous state be referred to as a vapor?
Explain. - Describe how the sharpening of a pencil is a different type of physical change than dissolving some sugar in
water.
Problems
Use theTable2.1 to answer the following questions.
TABLE2.1: Properties of Substances
Substance Color Melting Point (°C) Boiling Point (°C)
Bromine red-brown -7 59