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Physical Change and Chemical Change - Examples, Differences, Definition and Activities

 

Introduction and Overview

Changes are a natural aspect of life and are constantly present. Sometimes just one substance is involved. Whereas other times two or more than two substances are involved. Everything is an illustration of change, from dissolving salt in the water to churning of milk.

A change in the condition or state of the material occurs during some of the changes. While in others, the substance's current bonds break, leading to the formation of new bonds. It leads to the formation of new substances. There are two types of changes:

  • Physical changes
  • Chemical changes

Physical Changes

  • The physical state and appearance of a compound change during a physical change but the molecular composition remains unchanged. There is no new substance formed.
  • Color, texture, temperature, form, condition, and a variety of other factors may all undergo alterations due to physical change.
  • The physical qualities of a substance that change are lustre, malleability, ductility, density, mass, volume, solubility, and viscosity.
  • For a physical change, no amount of energy is required. As a result, no energy is needed to reverse it.
  • Physical changes are reversible since they are temporary. Hence, these changes are also called temporary changes.

Examples

  • A crumpled sheet of aluminum foil
  • Boiling of water
  • Casting silver into a mold
  • Evaporation of alcohol
  • Dry ice is sublimated into carbon dioxide vapor

Chemical Changes

  • The molecular composition of material changes completely during a chemical change, resulting in new substances. The chemical identity of the substance changes.
  • During a chemical reaction, the chemical composition and properties of the reactants change entirely.
  • In a chemical reaction, there is the involvement of energy. The energy difference between the breaking of existing bonds and forming of new bonds is equivalent to the energy involved in a chemical change. During a chemical reaction, this energy is either absorbed or released, generally in the form of heat.
  • The chemical changes are irreversible and permanent. However, they can occasionally be reversed by undergoing another chemical process.

Examples

  • Burning of paper
  • Cooking food
  • Souring of milk
  • Rusting of a metal
  • Fireworks exploding

Difference Between Physical and Chemical Change

PHYSICAL CHANGE CHEMICAL CHANGE Physical changes are temporary and reversible. Chemical changes are permanent and irreversible. In a physical change, only the physical properties of a substance are affected. The composition, physical and chemical properties change during a chemical change. No new substance is formed. One or more new substances are formed. In a physical change, the composition remains the same, but the molecules of the matter undergo rearrangement. In a chemical change, the molecular composition changes. A little or no energy is absorbed or released. Production and absorption of energy take place. In a chemical reaction, the primary form of energy involved is thermal energy.

Did you Know?

A chemical change leaves behind indicators to suggest that a chemical reaction might be underway. These indicators can be

  • Detectable odour
  • Change in temperature
  • Change in colour
  • Formation of bubbles
  • Formation of gas
  • Formation of a precipitate
  • Increment and decrement in the mass of the reactants
  • Heat or ultraviolet radiations are absorbed

A chemical reaction in which the energy is absorbed is known as an endothermic process. A chemical reaction where the energy is released is known as an exothermic process.

Chemical changes are greatly studied using thermodynamic systems, whereas physical changes can be studied by mere observation.

Activities

Put some ice cubes in a jar and set them aside. Place the container in a warm area. After a few minutes, the ice melts and gets converted to water. Place this container of water in the freezer once more. The ice is formed after one hour. This change that involves only a change in the state of matter is called a physical change.

Use magnesium in the form of a thin strip or ribbon. Using sandpaper, clean the tip of the strip or ribbon. Place the strip or the ribbon on the flame of a burning candle. It emits a bright white light when lit. When entirely burned, it leaves fine ash behind. This change that caused the emission of bright light and residues, is because of the formation of a new product, hence the change is called a chemical change.

The change that occurred is: Magnesium (Mg) + Oxygen (O2 ) → Magnesium oxide (MgO)

Fig 2: Reaction of metals with oxygen

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