Physical Properties and Changes

Chapter 7, Lesson 3

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.

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.

Physical Properties (cont’d)

•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.

Physical Properties (cont’d)

• Pressure also affects the boiling point

• The higher the air pressure, the higher the boiling point.

Physical Properties (cont’d)

• 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 substance’s density is higher when its

particles are packed more tightly together.– D =

Physical Properties (cont’d)

• 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.

Physical Properties (cont’d)

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

Physical Properties (cont’d)

• 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.

Physical Properties (cont’d)

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

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.

What is a physical change? (cont’d)

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

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)

7-3: Lesson Review Questions

1) When water changes to ice, it is undergoing a ____.

Achemical change

Bphysical change

C radioactive decay

Dmetallic change

7-3: Lesson Review Questions

2) Which of the following is NOT a physical change?

A ice melting into water

Bsugar dissolving into water

Csand and sugar mixing

Dburning a candle

7-3: Lesson Review Questions

3) Which of the following is NOT a physical property?

Adensity

Bconductivity

Chardness

Dall are physical properties