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 → Matter and its states ↓


Melting and freezing


In this lesson, we will explore two important processes of matter: melting and freezing. Melting and freezing are two changes of state that you often see in everyday life. When matter changes its form from one state to another, it undergoes a phase change. Let's take a deeper look at each of these phase changes to better understand them.

Understanding the states of matter

Matter is found in three main states: solid, liquid, and gas. Each of these states has its own distinct characteristics, based on how the tiny particles, called atoms or molecules, are arranged and move. Let's take a brief look at these states:

Solid: In the solid state the particles are packed very closely with each other in a fixed, ordered arrangement. These particles vibrate but do not move from their position. This causes solids to have a definite shape and volume. For example, ice is a solid form of water.

Liquids: In the liquid state, the particles are still close together but not in an ordered arrangement, and they can slide past each other, causing the liquid to flow. Liquids have a fixed volume, but they take the shape of their container. Water is an example of a liquid state.

Gas: In the gas state the particles are far apart compared to solids and liquids and they move freely at high speeds. Because of this gases have neither a definite shape nor a definite volume. Water vapor is water in the gas state.

State of matter particle arrangement Solid Liquid Gas

Melting process

Melting is the process in which a solid substance turns into a liquid. This happens when a solid substance is heated. Heat is a form of energy, and adding heat to a solid substance gives the particles more energy, which makes them vibrate faster. When they get enough energy, they can break free from their fixed position and start moving around freely, turning them into a liquid.

Example: Consider a chocolate bar. When you hold it in your hand, your body heat warms it up, causing it to melt.

Melting point

Every substance has a certain temperature at which it melts, called the melting point. At this temperature, a solid turns into a liquid. For example, the melting point of ice is 0 o C (32 o F).

Melting Point of Ice: 0°C or 32°F

Ice making process

Freezing is the opposite of melting. It is the process in which a liquid turns into a solid. When a liquid cools, it loses heat energy. As the particles lose energy, they move more slowly and begin to come together, arranging themselves in fixed positions, forming a solid.

Example: When you put water in an ice tray in the freezer, the water cools and freezes and turns into ice.

Freezing point

The freezing point is the temperature at which a liquid becomes a solid. Usually the freezing point and melting point are the same. Therefore, the freezing point of water is also 0 o C (32 o F).

Freezing Point of Water: 0°C or 32°F

Factors affecting melting and freezing

Pressure

Pressure is the force applied to a substance. Changes in pressure can affect the melting and freezing points of a substance. Generally, increasing pressure lowers the melting point of ice, which is why ice skates glide more easily on ice. The pressure from the skate blade momentarily melts the ice, making it easier to glide.

Impurities

Adding impurities to a substance can change its melting point and freezing point. For example, when salt is added to snow, it lowers the melting point, helping to melt ice on roads in the winter.

Observing melting and freezing in everyday life

We see melting and freezing around us every day. Here are some examples you may recognize:

  • Melting Ice Cream: On a sunny day, ice cream cones tend to melt and drip.
  • Freezing the Popsicles: Homemade juice popsicles are made by freezing fruit juice in molds.
  • Melting butter: Butter is melted on a hot pan before it is used for frying.
  • Freezing Rain: In winter, rainwater freezes when it hits cold surfaces, forming ice.

Phase change diagram

Phase changes can be represented in a diagram known as a "phase change diagram" or "heating curve." It shows how a substance such as water changes from a solid to a liquid and then to a gas with the addition of heat.

Phase change diagram Solid Liquid Gas Melting point Boiling point

Experiments to observe melting and freezing

You can do simple experiments to see the process of melting and freezing. Here is an easy activity you can try:

Experiment: Melting Ice

Required Materials:

  • a few ice cubes
  • a plate or bowl

Process:

  1. Place some ice cubes on a plate.
  2. Observe them as they begin to thaw at room temperature.
  3. Note the time it takes for the ice to completely turn into water.

As the ice melts, you will notice that it will become liquid, demonstrating the melting process.

Experiment: Making Ice

Required Materials:

  • a plastic ice tray
  • Water
  • a freezer

Process:

  1. Fill the ice tray with water.
  2. Place it carefully in the freezer.
  3. Check the tray after a few hours to see how the water has turned into ice.

This transformation of water into ice is an example of the process of freezing.

Conclusion

Understanding melting and freezing is fundamental in the study of matter and its states. These processes are all around us, affecting everything from how we enjoy our favorite dishes to the operation of the natural world. By observing and experimenting with melting and freezing, we gain a better understanding of how substances interact with temperature, causing changes in their states.

The concepts of melting and freezing not only provide insight into the physical world but also form the basis for more advanced studies in chemistry and physics. These phenomena remind us of the amazing changes that can occur in the smallest structures of matter due to simple changes in energy and temperature.


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Melting and freezing

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