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 (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.

5. Physical Properties (cont’d) • Pressure also affects the boiling point • The higher the air pressure, the higher the boiling point.

6. 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 =

7. 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.

8. Physical Properties (cont’d) • The table below shows the difference between the structure of diamonds and graphite, both of which are forms of carbon.

9. 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.

10. Physical Properties (cont’d) • 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? (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

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