Content Focus: Changes in Matter

Key Content Ideas (K-2)
• Matter can change when heating or cooling (shape, reaction)
• Some changes in matter are reversible, others irreversible

Key Content Ideas (3-5)
• Materials can be mixed and may (or may not) originate new substances.
• New substances can be identified by their properties

This sub-area focuses on physical and chemical changes in matter. During a physical change, a substance changes form but not chemical composition. During a chemical change, a new substance with a different composition and properties is formed. Matter can change when heated or cooled. Chemical changes also may occur when two or more substances are mixed. Some changes in matter are reversible, while others are irreversible. Observations of the quantitative properties (e.g., mass, density) and qualitative properties (e.g., state of matter, color, texture, and odor) of the substances are used to determine what type of change occurred.

In grades K-2, this sub-area is typically explored through observing the effects on matter by heating or cooling. Changes caused by heating and cooling may be reversible or irreversible. As an example of a reversible change, ice can be melted into liquid water by heating and then refrozen into ice. The cooking of an egg is an example of an irreversible change; upon cooling, the egg does not revert to its original form.

In grades 3-5, this sub-area is typically explored in the context of planning and carrying out investigations to produce data that will serve as evidence that mixing two or more substances may have resulted in a chemical change. An investigational plan will include observations and measurements of quantitative and qualitative properties of the substances before and after they are mixed. Also included in the plan can be methods, such as controlling the variables and running multiple trials, to ensure reliable data. Examples of reactions that produce observable changes include baking soda and vinegar (gas production) and milk and vinegar (curdling).