Physical Properties and Changes

1
Physical Properties and Changes

• Chapter 7, Lesson 3

2
What is a physical property?

• A physical property is any characteristic of a
  material that can be observed without changing
  the identity of the material itself such as
  color, shape or length.
• Some physical properties, such as mass and
  volume, depend on the amount of matter other
  physical properties do not depend on the amount
  of matter.

3
Physical Properties

• The temperature at which a solid changes to a
  liquid is its melting point. This does not
  depend on the amount of matter.
• The temperature at which a liquid changes to a
  gas is its boiling point. This does not depend
  on the amount of matter.

4
Physical Properties (contd)

• Attractive forces determine the melting and
  boiling points of a substance.
• Molecules with weak attraction have low melting
  and boiling points.
• Molecules with strong attraction have high
  melting and boiling points.

5
Physical Properties (contd)

• Pressure also affects the boiling point
• The higher the air pressure, the higher the
  boiling point.

6
Physical Properties (contd)

• Density is a physical property of a substance
  that does not depend on the amount of matter.
• Density is the mass-per-unit volume of a
  substance.
• A substances density is higher when its
  particles are packed more tightly together.
• D

7
Physical Properties (contd)

• Hardness is a physical property that shows how
  strongly the particles of a substance are held
  together.
• Diamonds are a form of carbon and are the hardest
  substance found in nature.

8
Physical Properties (contd)

• The table below shows the difference between the
  structure of diamonds and graphite, both of which
  are forms of carbon.

9
Physical Properties (contd)

• Thermal conductivity is the ability of a material
  to transfer heat.
• When one part of a metal is heated, the particles
  collide into other particles and the heat is
  transferred throughout.

10
Physical Properties (contd)

• Electrical conductivity is the ability of a
  material to transfer electric charge.

11
What is a physical change?

• A physical change is any change in size, shape,
  or state of matter in which the identity of the
  substance is not changed.
• Dissolving is a physical change in which one
  substance is mixed into another substance to form
  a solution.
• Mixing is a physical change that takes place when
  two substances are combined and neither substance
  dissolves.

12
What is a physical change? (contd)

• Changes in the state of matter of a substance are
  physical changes and are reversible
• Melting and freezing
• Boiling and condensing
• Subliming and deposing

13
What is a chemical change?

• In comparison, a chemical change is the change of
  one or more substances into other substances.
• A chemical change can not be reversed
• Burning paper ash, CO2, H2O
• Baking soda vinegar CO2, H2O
• Rust FeO (iron oxide)
• (more to come in Chapter 8)

14
7-3 Lesson Review Questions

• 1) When water changes to ice, it is undergoing a
  ____.
• A chemical change
• B physical change
• C radioactive decay
• D metallic change

15
7-3 Lesson Review Questions

• 2) Which of the following is NOT a physical
  change?
• A ice melting into water
• B sugar dissolving into water
• C sand and sugar mixing
• D burning a candle

16
7-3 Lesson Review Questions

• 3) Which of the following is NOT a physical
  property?
• A density
• B conductivity
• C hardness
• D all are physical properties