Students’ Learning Outcomes
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Investigate the effect of heat on particle motion during a change in states · Demonstrate and explain the processes that are involved in the change of states.
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Information for Teachers
· When a solid is heated the vibration movement of its particles increases. At a certain temperature, the solid changes into its liquid. This process is called melting.
· When a liquid is heated, its particles get more energy and move away from one another. At a certain temperature these particles become independent of one another and the liquid is converted into a gas. This process is called boiling.
Material / Resources
Plastic balls, tray, ice, plate ice cubes, textbook
Worm up Activity
Ask the students:
· What happen to ice when it is heated?
(Students response: ice melts)
· What happens to water if you put it in the freezer?
(Students response: it freezes into ice)
· Introduce the topic “Effect of Heat on particle motion” and write the topic on the board.
Development
Activity 1
· Draw the following three figures on the writing board or show the chart having the following figures.
· Ask two students to come forward and arrange the plastic balls in a tray as shown in the figure 1
· Disturb the arrangement of the balls as shown in the figure 2
· Spread the plastic balls away from one another as shown in the figure3
Ask the students the following question:
· Which states of matter are represented by these three figures?
(Students response: figure 1 represents the regular arrangement of particles in solids.
· Figure 2 represents the irregular arrangement of particles in liquids.
· Figure 3 represents the particles of gases. These particles are far apart from each other)
· Is there a force of attraction present between the particles of a solid?
(Students response: Yes, the particles of a solid attract each other with a strong force of attraction)
· Are these particles moving?
(Students response: Yes, the particles are vibrating at a fixed position.
· What type of movement these particles have in each state?
(Students response: the particles of a child can only vibrate while the particles of a liquid and gas can move in all directions
Activity 2
· Take a piece of ice on a plate and let it melt with the help of a candle.
· Inform the students that:
——-Heat has changed the solid ice into liquid water.
——-This process is called melting and temperature at which ice melts is called the melting
point of ice.
——-when a solid is heated, its particles start vibrating faster and attraction between these
particles gets less effective. At a particular temperature, the particles lose their fixed
positions and the arrangement in them goes away and the solid loses its fixed shape.
—– It is converted into its liquid.
Activity 3
· Take water in kettle / beaker heat it so that water starts boiling.
· Inform the students that:
· Heat has changed the liquid water into steam (gas)
· This process is called boiling and the temperature at which a liquid boiles in an open vessel is called its boiling point.
· When a liquid is heated, its particles start moving at a higher speed. The force of attraction between them becomes less effective.
· At a particular temperature the force of attraction between these particles gets so infective that they become independent of one another.
· The liquid is converted into a gas.
Activity 4
· Divide students in groups. Ask each group to pour molten wax on a plate.
· Ask them what has happened to the wax that is poured on the plate?
(Students responses: The wax become solid)
· Why liquid wax is changed into solid wax when poured on the plate?
( Students response: Due to cooling the wax freezes when poured on the plate and becomes soild)
· Ask them what happen to the particles of a liquid that changes into solid?
(Students ‘ response: When a liquid loses its energy, its particles start arranging themselves and their movements slow down appreciably.
As a result the liquid freezes and changes into solid. In solid the particles simply vibrate at their fixed positions.
· Can water also become solid when poured on a plate? (Students’ response: No)
· Why not? (students’ reponse: because water needs more cooling than wax.
· Ask them how can you freeze water to change it into ice? (students’ response: keeping water in the freezez of a refrigerator until water freezes )
· Explain them that the changing of a liquid into solid is called freezing.
· Explain them the changes of a liquid them that changing of a liquid them that the changing of a liquid into solid is called freezing.
Sum Up / Conclusions
· A solid can be changed into its liquid form by heating. The process is called melting.
· A liquid can be changed into its gaseous form by heating. At a particular temperature the vaporization becomes maximum and the liquid starts boiling. This process in known as boil
Assessment
Ask the students the following questions:
· Particles of which state of matter move with the fastest speed? (Students’ response: particles of a gas move with the fastest speed)
· What makes a solid lose its shape? (students’ response: since the particles of a solid, on heating, lose their fixed positions, so their shape is also lost)
· Why does a gas not have fixed shape and a fixed volume? (Students’ response: particles of a gas are moving fast without any significant force of attraction between them.
· They behave independently and don’t have fixed position. Due to these characteristics gases neither have fixed shape nor a fixed volume)
· Involve the students in solving the questions given at the end of chapter / unit I textbook.
Follow up
· When you heat solid ice, it changes into water. How can you convert liquid water into solid ice? (expected response: by putting it changes in a freezer, the temperature of water will drop i
