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7th Grade Physical and Chemical Changes Worksheets (Definition and Examples)

 

Grade 7 Science Worksheets

Physical changes involve alterations in the form or state of matter without affecting its chemical composition. These changes are typically reversible, and examples include melting, freezing, and boiling. On the other hand, chemical changes result in the formation of new substances with distinct chemical properties. These changes are often irreversible and involve chemical reactions, such as rusting of iron or burning of wood.

physical and chemical changes

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Physical Properties: A physical property of a substance means its shape, size and physical state of a substance. For example: when water boils it turns to vapor but its still water in gaseous form. Although its state changes.

Chemical Properties: The basic inherent nature of a substance is known as chemical properties. For example mold on a piece of bread. Once yeast is formed, we would never get the original bread form.

physical and chemical changes

All such changes can be separated into two types – Physical and Chemical.

What are the physical changes?

  • Physical changes are the changes in physical properties which does not involve new produce of substances.  Changes are very much reversible like – melting of ice.

Nature of a Physical change –

  • Physical changes are mostly reversible
  • Physical properties of a substance only changes not its chemical properties
  • New substance is not created in this process
physical and chemical changes

Chemical Changes

Chemical changes are permanent changes which happen to the original substances making it lose its inherent properties. Changes like these are irreversible like – rusting of iron, burning of wood.

Credit: https://pixabay.com/en/chain-rust-iron-metal-macro-rusty-566778/

Nature of a Chemical change :

  • A chemical change cannot be brought to original by physical methods. Chemical properties of substance change
  • In a chemical change, new substances are formed
  • Chemical changes are not reversible
  • The chemical composition and properties of a substance changes during a chemical chnage
  • Gas evolves

Results of Chemical Change :

  • Change in smell.
  • Gas evolves.
  • Heat is produced.
  • Sound is produced.
  • Change in color. 

What is an example of a physical change?

Heating of water: When water is heated no new substance is formed. No change in color or smell.

Paper folding:  A paper can be folded or refolded and unfolded again hence it is an example of physical change. Here, no new substance is formed in this. So, it is a physical change. 

Molding of clay: Clay when molded. Shape changes, its size changes but no gas evolves, or no new substance is formed and no smell is produced. 

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Cutting of wood: When we cut a piece of wood we get more number of wood pieces but there is no new substance produced, no gas evolution and no change in the property of wood.

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Crushing paper: Here, again no new substance is formed. Can be brought back to its original form. No gas is released.

Mixing salt in water: Water and salt can be easily separated. This is a physical change because no new substance is formed and the chemical properties of substances involved are completely intact. 

Chemical Changes

When properties of substance change and new substances are formed is called chemical changes. Sometimes chemical changes are irreversible.  In chemical change  where it can be reversed chemical properties of substance alter and a new substance is formed. 

What is an example of a chemical change?

Burning of anything like paper, wood, fuel etc. When a substance burns, many new substances are formed like ash and carbon dioxide is formed.  A burnt substance cannot be turned to the original form by any chance since ash is what remains.

Hence, burning of a substance is an irreversible chemical change.

Wax melting: This is a reversible change because wax solidifies in room temperature. There is no new substance formed. No gas emissions and chemical property of wax does not change.

Physical and Chemical Changes Worksheets

Cooking vegetables: This involves baking or frying of food which then cannot be brought back to the original self. Smell is produced. It’s a new substance altogether.

Digestion is an example of chemical change. New substances are produced. Food is broken down. Energy is released, cannot be converted to food again.

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Weathering of rocks: Rock formation involves immense heat and pressure. Running water on them, intense wind and expansion as a result of heat. These changes are irreversible.

Weathering of rocks

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Check Point

I. State True or False –

  1. Melting of wax is a chemical change.
  2. A physical change involves formation of new products.
  3. A chemical change is irreversible.
  4. Burning of paper is a chemical change.
  5. Chemical change cannot be reversed by simple physical means.
Answer Key
  1. False
  2. False
  3. True
  4. True
  5. True
What is a physical change?

A physical change refers to a transformation in the physical properties of a substance without altering its chemical composition. This means that the substance remains the same at the molecular level, and the change is often reversible. Examples of physical changes include changes in state (solid to liquid to gas), dissolving, cutting, and bending.

What is a chemical change?

A chemical change, also known as a chemical reaction, occurs when one or more substances react to form new substances with different chemical properties. During a chemical change, the atoms and molecules rearrange and bond differently, leading to the formation of entirely new substances. Chemical changes are typically irreversible. Examples include combustion, rusting, and fermentation.

How can we differentiate between a physical and a chemical change?

The key difference lies in whether the change affects the chemical composition of the substance. In a physical change, the substance remains the same at the molecular level, whereas in a chemical change, new substances with distinct properties are formed. Additionally, physical changes are usually reversible, while chemical changes are not.

Is boiling water a physical or a chemical change?

Boiling water is a physical change. During boiling, water changes its state from a liquid to a gas (water vapor), but its chemical composition remains H2O molecules. When the water vapor cools down, it condenses back into liquid water, demonstrating the reversibility of this physical change.

Why are chemical changes considered irreversible?

Chemical changes involve the formation of new substances with different chemical properties, and reversing these reactions would require different conditions and reactions. Once the chemical bonds are broken and new ones are formed, it is challenging to revert to the original substances, making chemical changes irreversible.

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