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 ____. A chemical change B physical change C radioactive decay D metallic change

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

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