Chapter 3 Section 3
1.5 class periods
3-3 Chemical Properties and Changes
In this section students will learn that the physical and chemical properties of a substance are useful in determining the identity of a substance. The properties that distinguish one substance from another without changing the substance are called physical properties. The properties that describe how a substance changes into another new substance are called chemical properties. Students will investigate flammability, or the ability of a substance to burn, as a chemical property. They will discover that the substance produced by the burning is a new substance that has been altered by the chemical change. Thus flammability is a chemical property, and burning is a chemical change. They will note that another name for a chemical change is a chemical reaction.
The themes that can be focused on in this section are energy, patterns of change, and systems and interactions.
Energy: Point out that substances can be made to change phase by adding or taking away energy, but that in a chemical change energy is released from or added to the particles making up the old substance to create the particles making up the new substances. Sometimes energy must be added to produce a chemical change, and sometimes a chemical change releases energy. Breaking up water into hydrogen and oxygen is an example of the first. The burning of hydrocarbons is an example of the second.
Patterns of change: Explain that a chemical change effects a change in the particles of a substance. Point out that the particles of a substance are indeed made of smaller particles that do not undergo a change when they are rearranged to form the new substances.
Systems and interactions: Note that during a chemical reaction, new substances with different physical and chemical properties are produced. Two or more substances, each with its own physical and chemical properties, interact under certain conditions to produce one or more new substances, each with its own physical and chemical properties.
Performance Objectives 3-3
Science Terms 3-3
Chemical property, p.76
Chemical change, p.77
Chemical reaction, p.77
Show students a wooden splint.
Light a match and set the splint on fire. Let it burn until at least half of it has become charred or has fallen off as ash.
Point out that chemical properties describe ways in which substances change into other substances.
Light a small candle, in a holder, then blow it out.
Re-light the candle, cover the candle with a 500-mL beaker.