Grade 5 | Science | Unit 2 - Concept 3 - Lesson 2 - Temperature and state of matter

Welcome dear students!
Melting
• In this process, the particles of a solid matter gain energy.
• This causes particles to move around more and their temperature increases.
• So, the matter changes to liquid state.
• For example:
• When the temperature of solid ice increases above 0°C, its particles gain energy and they move around more, so the ice changes to liquid water.
Freezing
• In this process, the particles of liquid matter release energy.
• This causes particles to move slower and their temperature decreases.
• So, the matter changes to solid state.
• For example :
• When the temperature of liquid water decreases below 0°C, its particles release energy and they move slower, so liquid water changes to solid ice.
Notes
1. (°C) is the measuring unit of temperature.
2. 0°C is known as the freezing point of water.
3. Water is found in liquid state between 0°C and 100°C.
• Melting of ice and freezing of water are examples of a change in the state of matter.
• Changing the state of matter is considered as a "physical change".
But, what is meant by physical change?
Physical change:It is a change in matter without any change in its structure.
Example: When chocolate melts, it changes from solid state to liquid state, but its taste, color and smell don't change.
• Physical changes are usually reversible such as melting is the reverse process of freezing.
Changing a solid to a liquid (Melting)
When placing a container of ice cubes on a hot stove:
The ice gains thermal energy.
So, the particles of ice move faster and separate from each other.
This causes the change of the ice from solid state to liquid state (water).
Changing a liquid to a solid (Freezing)
When placing a water container in a freezer :
The water loses the thermal energy to the space in the freezer.
So, the particles of water move slower and get close together.
This causes the change of the water from liquid state to solid state (ice).
Changing a liquid to a gas (Evaporation)
When boiling a water container on a hot stove:
1. The water gains thermal energy.
2. So, the particles of water move more faster and separate much more from each other.
3. This causes the change of the water from liquid state to gas state (water vapor).
Changing a gas to a liquid (Condensation)
When water vapor touches a cold surface:
1. The water vapor loses the thermal energy to the cold surface.
2. So, the particles of water vapor move slower and get close together.
3. This causes the change of water vapor from gas state to liquid state (water).
Note: Water vapor differs from steam
• When water boils, it produces water vapor which is invisible in the air.
• When the water vapor hits cooler air, it condenses into tiny water droplets forming a visible small white cloud known as steam.

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Mr. Raouf Ashraf