Grade 6
  1. Introduction to Chemistry  1.1. What is Chemistry?  1.2. Importance of chemistry in daily life  1.3. Branches of chemistry  1.4. Safety rules in chemistry laboratory  1.5. Common Laboratory Equipment and Their Uses
  2. Matter and its states  2.1. Definition of Matter  2.2. Properties of matter  2.3. States of matter  2.4. Solid state  2.5. Fluid state  2.6. Gaseous state  2.7. Plasma state  2.8. Changes in the states of matter  2.9. Melting and freezing  2.10. Evaporation and Condensation  2.11. Sublimation  2.12. Deposit
  3. Physical and chemical changes  3.1. Definition of Physical Change  3.2. Examples of physical change  3.3. Definition of Chemical Change  3.4. Examples of chemical change  3.5. Difference Between Physical and Chemical Changes  3.6. Indicators of Chemical Change
  4. Elements, Compounds, and Mixtures  4.1. Definition of the element  4.2. Classification of elements  4.3. Metals  4.4. Non metallic  4.5. Metalloids  4.6. Noble gases  4.7. Definition of compound  4.8. Properties of Compounds  4.9. Definition of Mixture  4.10. Types of mixtures  4.11. Homogeneous mixture  4.12. Heterogeneous mixtures
  5. Separation of mixtures  5.1. The need for isolation  5.2. Separation methods  5.3. Handpicking and winnowing  5.4. Filtration  5.5. Sedimentation and decantation  5.6. Evaporation  5.7. Crystallization  5.8. Distillation  5.9. Magnetic Separation  5.10. Chromatography
  6. Air and its composition  6.1. Components of air  6.2. Importance of Oxygen  6.3. The importance of nitrogen in the air and its composition  6.4. Carbon dioxide in the atmosphere  6.5. The role of water vapor and other gases in air and its composition  6.6. Properties of Air  6.7. Uses of air  6.8. Air pollution and its effects
  7. Water and its properties  7.1. Importance of Water  7.2. Sources of water  7.3. Properties of water  7.4. Water as the universal solvent  7.5. Water Purification  7.6. Water purification methods (boiling, filtration, chlorination)  7.7. Water cycle  7.8. Water conservation  7.9. Water pollution and its effects
  8. Acids, Bases and Salts  8.1. Definition of Acid  8.2. Properties of Acids  8.3. Examples of Acids  8.4. Definition of Bases  8.5. Properties of bases  8.6. Examples of Bases  8.7. Definition of Salt  8.8. Neutralization reaction  8.9. pH Scale and Indicators  8.10. Uses of Acids, Bases and Salts
  9. Introduction to the Periodic Table  9.1. History of the Periodic Table  9.2. Arrangement of elements in the periodic table  9.3. Groups and periods  9.4. Importance of periodic table  9.5. First 10 elements and their symbols
  10. Metals and Nonmetals  10.1. Properties of Metals  10.2. Properties of Non-Metals  10.3. Difference Between Metals and Nonmetals  10.4. Uses of metals and nonmetals  10.5. Corrosion of metals and its prevention
  11. chemical reactions  11.1. Introduction to Chemical Reactions  11.2. Types of Chemical Reactions  11.3. combustion reaction  11.4. Oxidation and Reduction  11.5. Simple chemical equations  11.6. Rusting of iron
  12. Fuel and energy  12.1. Types of fuel  12.2. Fossil fuels  12.3. Renewable and non-renewable sources of energy  12.4. Energy Conservation  12.5. Alternative sources of energy (solar, wind, hydropower)
  13. Plastic and fiber  13.1. Natural and synthetic fibers  13.2. Properties of plastics  13.3. Advantages and disadvantages of plastic  13.4. Recycling of plastic  13.5. Biodegradable and non-biodegradable materials

Grade 6 → Physical and chemical changes ↓


Difference Between Physical and Chemical Changes


In the wonderful world of chemistry, everything around us is made up of tiny building blocks called atoms and molecules. These can undergo changes that are divided into two main categories: physical changes and chemical changes. Understanding the difference between these two types of changes is essential to knowing how matter interacts in our universe.

What is a physical change?

A physical change affects the appearance of a chemical substance, but not its chemical composition. This means that a substance that undergoes a physical change remains the same substance. These changes are usually reversible and involve changes in physical properties such as shape, size, phase (e.g. solid, liquid, gas) and density.

Examples of physical change

  • Melting ice to make water
  • Boiling water into steam
  • Breaking the glass
  • Masturbation
  • Crushing the can

Visual example: melting snow

Ice 🧊 water 💧

What is a chemical change?

On the other hand, a chemical change occurs when a substance combines with another substance to form a new substance. This process often involves making or breaking chemical bonds and results in substances with new chemical properties. Chemical changes are usually not easily reversible.

Examples of chemical change

  • Burning wood produces ash and gases
  • Rusting of iron
  • Baking the cake
  • Souring of milk
  • Making Carbon Dioxide Gas by Mixing Baking Soda and Vinegar

Visual example: vinegar and baking soda reaction

Baking Soda (NaHCO3) Vinegar (CH3COOH) + Reacts to production Carbon dioxide (CO2) gas

Indicators of Chemical Change

Identifying a chemical change can sometimes be challenging, but there are several signs we can look for. Here are some signs that a chemical change has occurred:

  • Discoloration (e.g., rusting of iron)
  • Formation of precipitate (solid substance formed from solution)
  • Gas production (bubbles or smoke)
  • Change in temperature (the reaction may release or absorb heat)
  • Changes in light or sound (e.g., explosions or light emissions)

Lesson example: baking a cake

Baking a cake is a delicious example of a chemical change. When you combine ingredients such as flour, eggs, sugar and baking powder, the heat from the oven causes the baking powder to release carbon dioxide gas. This gas makes the cake rise and gives it a fluffy texture. Also, proteins and carbohydrates undergo reactions that give the cake its delightful taste and aroma.

Caking Baking Reaction:
Baking soda (NaHCO3) + acid (e.g., vinegar) → carbon dioxide (CO2)

Detailed comparison

Reversibility

One of the primary differences between physical and chemical changes is reversibility. Physical changes, such as melting or freezing, can generally be reversed. For example, water can freeze into ice and then melt back into water.

Chemical changes usually cannot be reversed by simple physical means. For example, once wood is burned to ashes, it cannot be turned back into wood.

Energy transformation

Both physical and chemical changes can involve energy changes.

  • The energy changes in physical changes are usually small, such as the energy needed to change the phase of water.
  • Chemical changes often involve significant energy transformations, such as the release of heat during combustion.

Changes in structure

The composition of matter remains the same during physical changes. Chemically, ice and water are both H2O

In chemical changes the composition of matter changes. For example, burning methane in oxygen produces carbon dioxide and water.

Methane combustion reaction:
CH4 + 2O2 → CO2 + 2H2O

Visual representation of the differences

Consider the following simplified visualization:

Physical changes Reversible Chemical change Not reversible

Conclusion

Understanding the difference between physical and chemical changes is a foundational concept in chemistry. While both types of changes can occur naturally, seeing them in action—such as water boiling, bread baking, or leaves changing color—helps us understand the processes at work. Identifying whether a change is physical or chemical gives us information about the nature of matter and the universe. It also allows chemists to purposefully manipulate substances, contributing to advances in technology, medicine, and countless other fields.


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Difference Between Physical and Chemical Changes

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