Physical and Chemical Properties and Changes

​There are two types of changes in matter; physical change and chemical change. As the names suggest, a physical change affects a substance’s physical properties and a chemical change affects its chemical properties.

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• ​occur when there is a change to one or more physical properties

• ​does not result in a change in chemical identity

• are reversible​ in many cases

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• occur when one substance changes into another​ after a chemical reaction

• ​"ingredients" are called reactants and end results are called products

• irreversible​

• Production of gas/bubbles​

• Production of odor

• Change in color

• Formation of precipitate

• Exothermic/Endothermic reaction

• ​Release of light

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Identifying chemical changes

​Signs of a chemical change

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Chemical reactions tend to happen more quickly at higher temperatures. When temperatures are higher, atoms and molecules have more kinetic energy which enable them to move around and rearrange more quickly and easily.

This law states that mass cannot be created or destroyed during a physical or chemical change. The mass you have before the change is always equal to the mass after the change. For example, a chemical reaction between 93g of mercury and 7g of oxygen will produce 100g of mercuric oxide.

• Building an Argument about Changes:

  • We can use what we see to show if a substance changes in two ways: physically or chemically.

  • Observing Physical Changes:

    • Changes in state (solid, liquid, gas) without forming new substances.

    • Changes in shape or size that can be reversed.

  • Observing Chemical Changes:

    • Color changes indicating a new substance is formed.

    • Formation of bubbles or gas, showing a chemical reaction.

    • Release of heat or light during the change process.

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• Backing Up Our Claims:

  • Give examples of changes we can see and explain why they are physical or chemical.

• Examples of Changes:

  • Physical Changes:

    1. Melting Ice: Ice becomes water, still the same substance.

    2. Tearing Paper: Paper rips into smaller pieces, but it's still paper.

  • Chemical Changes:

    1. Burning Wood: Wood becomes ash and smoke, not wood anymore.

    2. Rusting of Iron: Iron reacts with air to form rust, changing its makeup.