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Change of State | Science Class 5 PDF Download

You will learn about:

  1. Change of State of matter 
  2. Melting 
  3. Evaporation 
  4. Condensation 
  5. Freezing 
  6. Expansion and contraction of matter 

Introduction

Matter can change from one state to another on heating or cooling.

Change of State | Science Class 5

Melting 

Change of State | Science Class 5

When ice is kept out of a refrigerator, it melts into water. The process of changing a solid into a liquid on heating is called melting.
When ice is kept in a warm place, the molecules of ice start vibrating faster and become free from the rigid form. They become loosely packed to form water.

Evaporation 

Change of State | Science Class 5

When water is heated, it changes into water vapour. The process of changing of a liquid into a gas on heating is called evaporation. The molecules of water start vibrating faster on heating. They become free and escape into the air as gas. Molecules of a gas move much more freely.

Condensation 

Change of State | Science Class 5

When the steam touches a cold surface, it changes into water. The process of changing a gas into a liquid on cooling is called condensation. When molecules of steam or water vapour touch a cold surface, their movement slows down. They become less free to move and form water. 

Freezing 

Change of State | Science Class 5

When water is kept in a freezer, it changes into ice. The process of changing a liquid into a solid on cooling is called freezing. On cooling water, the molecules slow down and come very close to each other. They pack themselves into a rigid form to make ice.

Expansion and contraction of matter 

  • When we heat a substance, the molecules start vibrating rapidly. 
  • Due to this intermolecular space between the molecules increases and the substance expands
  • Thus, expansion is the increase in size of matter on heating. For example, tight metal lid of a jar can be opened easily by dipping it in hot water. 
    Change of State | Science Class 5
  • This happens because hot water causes the lid to expand a little and thus it opens out easily. 
  • Similarly, electric wires between electric poles hang loose in summer season. 
    Pole wires in SummersPole wires in Summers
  • On the other hand when we cool a substance, the movement of molecules slows down. 
  • Due to this intermolecular space between the molecules decreases and the substance contracts. 
  • Thus, contraction is the decrease in size of matter on cooling. For example, electric wires do not hang loose between electric poles in winter season. 

Change of State | Science Class 5

The document Change of State | Science Class 5 is a part of the Class 5 Course Science Class 5.
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FAQs on Change of State - Science Class 5

1. What is melting?
Ans. Melting is a process in which a solid substance changes into a liquid state due to the application of heat. This occurs when the substance's temperature reaches its melting point.
2. What causes expansion and contraction of matter?
Ans. Expansion and contraction of matter occur due to changes in temperature. When matter is heated, its particles gain energy and move faster, causing the substance to expand. On the other hand, when matter is cooled, its particles lose energy and move slower, leading to contraction.
3. How does the change of state occur?
Ans. The change of state occurs when a substance transitions from one physical state to another, such as from solid to liquid (melting) or from liquid to gas (evaporation). This change happens when the substance reaches a specific temperature, known as the melting point or boiling point.
4. What factors affect the melting point of a substance?
Ans. Several factors can influence the melting point of a substance. One significant factor is the strength of the intermolecular forces between its particles. Substances with stronger forces require more energy to break these bonds and therefore have higher melting points. Additionally, the purity and composition of the substance can also affect its melting point.
5. Can expansion and contraction of matter be reversible?
Ans. Yes, the expansion and contraction of matter can be reversible. When a substance expands due to heating, it contracts back to its original state when cooled down. This behavior is known as thermal expansion and contraction. However, it is important to note that irreversible changes can also occur in certain cases, such as when materials undergo physical or chemical reactions.
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