The weight of an object is always equal to the sum of its parts, regardless of how it is assembled. In a chemical reaction or physical change matter is neither created nor destroyed. When two or more materials are combined, either a chemical reaction or physical change may occur. Chemical reactions are often indicated when materials give off heat or cool as they take in heat, give off light, give off gas, or change colors. In a chemical reaction, materials are changed into new substances. In a physical change a new substance is not formed.
Standard 1: Students will understand that chemical and physical changes occur in matter.
Objective 1: Describe that matter is neither created nor destroyed even though it may undergo change.
Objective 2: Evaluate evidence that indicates a physical change has occurred.
Objective 3: Investigate evidence for changes in matter that occur during a chemical reaction.
Standard 1: Students will understand that chemical and physical changes occur in matter.
Objective 1: Describe that matter is neither created nor destroyed even though it may undergo change.
- Compare the total weight of an object to the weight of its individual parts after being disassembled.
- Compare the weight of a specified quantity of matter before and after it undergoes melting or freezing.
- Investigate the results of the combined weights of a liquid and a solid after the solid has been dissolved and then recovered from the liquid (e.g., salt dissolved in water then water evaporated).
- Investigate chemical reactions in which the total weight of the materials before and after reaction is the same (e.g., cream and vinegar before and after mixing, borax and glue mixed to make a new substance).
Objective 2: Evaluate evidence that indicates a physical change has occurred.
- Identify the physical properties of matter (e.g., hard, soft, solid, liquid, gas).
- Compare changes in substances that indicate a physical change has occurred.
- Describe the appearance of a substance before and after a physical change.
Objective 3: Investigate evidence for changes in matter that occur during a chemical reaction.
- Identify observable evidence of a chemical reaction (e.g., color change, heat or light given off, heat absorbed, gas given off).
- Explain why the measured weight of a remaining product is less than its reactants when a gas is produced.
- Cite examples of chemical reactions in daily life.
- Compare a physical change to a chemical change.
- Hypothesize how changing one of the materials in a chemical reaction will change the results.