Physical and Chemical Changes

A physical change is a change in which only the physical properties of a substance, such as shape, size, or state, are altered and a chemical change is a change in which the chemical composition of a substance changes, resulting in the formation of one or more new substances with different properties.

Example:

• Physical changes: melting of ice, boiling of water, cutting paper
• Chemical changes: rusting of iron, burning of wood, cooking of food

Physical Change

A physical change is a change in which only the physical properties of a substance (such as shape, size, or state) change, and no new substance is formed.

Example:

• Melting of ice
• Boiling of water
• Freezing of water
• Cutting or tearing of paper
• Breaking of glass

Characteristics of Physical Change

The important characteristics of a physical change are:

• No new substance is formed: The substance remains the same before and after the change.
• Only physical properties change: Properties such as shape, size, state, volume, or appearance may change.
• Chemical composition remains unchanged: The molecules of the substance remain the same.
• Usually reversible: Many physical changes can be reversed to obtain the original substance.
• Small energy change: Only a small amount of energy is absorbed or released, mainly during change of state.
• No chemical reaction occurs: The change does not involve breaking or forming of chemical bonds.
• Only arrangement of particles changes: The particles remain the same, but their arrangement or distance may change.

Chemical Change

A chemical change is a change in which one or more new substances are formed with different chemical properties due to a change in the chemical composition of the original substance.

Example:

• Rusting of iron
• Burning of wood
• Cooking of food
• Curd formation from milk

Characteristics of Chemical Change

The main characteristics of a chemical change are:

• Formation of a new substance: One or more new substances with properties different from the original substance are produced.
• Change in chemical composition: Atoms rearrange and new chemical bonds are formed, resulting in new molecules.
• Usually irreversible: Most chemical changes cannot be easily reversed to obtain the original substance.
• Energy change occurs: Chemical changes often involve the absorption or release of energy in the form of heat, light, or sound.
• Chemical reaction takes place: Bonds are broken and new bonds are formed during the process.
• Properties change completely: The new substance has different physical and chemical properties from the original substance.
• Observable changes may occur: Such as change in colour, evolution of gas, formation of a precipitate, or change in temperature.

Physical vs Chemical Change

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