Changes in states of matter

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Changes in states of matter

• 1. The changes in the states of matter are
  caused by heating or cooling. For example, ice
  melts when it is heated and water changes into
  ice when it is frozen.

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Changes in states of matter

• 2. The kinetic theory of matter is used to
  explain the changes in states of matter.

Melting
?When a solid is heated, the particles in the solid gain kinetic energy and vibrate more vigorously.
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Changes in states of matter

• 2. The kinetic theory of matter is used to
  explain the changes in states of matter.

Melting
?When a solid is heated, the particles in the solid gain kinetic energy and vibrate more vigorously. ?The particles vibrate faster as the temperature increases until the energy they gain is able to overcome the forces that hold them at their fixed positions.
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Changes in states of matter

• 2. The kinetic theory of matter is used to
  explain the changes in states of matter.

Melting
?When a solid is heated, the particles in the solid gain kinetic energy and vibrate more vigorously. ?The particles vibrate faster as the temperature increases until the energy they gain is able to overcome the forces that hold them at their fixed positions. ?At this point, the solid becomes a liquid.
Liquid
Solid
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Changes in states of matter

• 2. The kinetic theory of matter is used to
  explain the changes in states of matter.

Melting
?The temperature at which this happens is called the melting point. ?Melting point is the temperature at which a solid changes into a liquid at a particular pressure.
Liquid
Solid
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Changes in states of matter

• 2. The kinetic theory of matter is used to
  explain the changes in states of matter.

Freezing
?When a liquid is cooled, the particles in the liquid lose energy and move slower.
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Changes in states of matter

• 2. The kinetic theory of matter is used to
  explain the changes in states of matter.

Freezing
?When a liquid is cooled, the particles in the liquid lose energy and move slower. ?As the temperature continues to drop, the particles continue to lose more energy until they do not have enough energy to move freely.
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Changes in states of matter

• 2. The kinetic theory of matter is used to
  explain the changes in states of matter.

Freezing
? At this point, the liquid changes into a solid. ?The temperature at which this happens is called the freezing point. ?Freezing point is the temperature at which a liquid changes into a solid at a particular pressure.
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Changes in states of matter

• 2. The kinetic theory of matter is used to
  explain the changes in states of matter.

Boiling
?When a liquid is heated, the particles of the liquid gain kinetic energy and move faster as the temperature increases. ?Eventually, the particles have enough energy to completely break the forces holding them together.
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Changes in states of matter

• 2. The kinetic theory of matter is used to
  explain the changes in states of matter.

Boiling
?The particles are now able to move freely and far apart. ?A gas is formed. ?The temperature at which this happens is called the boiling point. Boiling point is the temperature at which a liquid changes into a gas at a particular pressure.
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Changes in states of matter

• 2. The kinetic theory of matter is used to
  explain the changes in states of matter.

Condensation
?When a gas is cooled, the particles in the gas lose energy and move slower. ?As the temperature drops, the gas particles lose energy and move more slowly.
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Changes in states of matter

• 2. The kinetic theory of matter is used to
  explain the changes in states of matter.

Condensation
?Eventually, the movements of the particles become slow enough for the gas to change into a liquid. ?This change occurs at the boiling point of the substance.
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Changes in states of matter

• 2. The kinetic theory of matter is used to
  explain the changes in states of matter.

Sublimation
Sublimation is a process by which a solid changes directly into a gas without passing through the liquid state and vice versa. Examples of substances that undergo sublimation are iodine, ammonium chloride, NH4Cl and dry ice (solid carbon dioxide).
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Changes in states of matter

• Experiment 2.2 To determine the melting and
  freezing points of naphthalene.
•  
• Aim To determine the melting and freezing points
  of naphthalene

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Changes in states of matter

• Experiment 2.2 To determine the melting and
  freezing points of naphthalene.
• Materials
• Naphthalene powder, water.

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Changes in states of matter

• Experiment 2.2 To determine the melting and
  freezing points of naphthalene.
• Apparatus
• Retort stand, beaker 250 cm3, boiling tube, a
  large conical flask, thermometer (0 -100C),
  stop watch, wire gauze, Bunsen burner.

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Changes in states of matter

• Procedure
• 1. A boiling tube is filled with naphthalene to
  a depth of 3 cm and a thermometer is put into it.

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Changes in states of matter

• Procedure
• 2. The boiling tube is suspended in a beaker
  half-filled with water using a retort stand and a
  clamp as shown in Figure 2.10. The level of
  naphthalene in the boiling tube is ensured to be
  below the level of water in the beaker.

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Inter-conversion of States of Matter and Kinetic
Theory of Matter

• Procedure
• 3. The water is heated and the naphthalene is
  stirred slowly with the thermometer.

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Changes in states of matter

• Procedure
• 4. When the temperature of the naphthalene
  reaches 60C, the stopwatch is started. The
  temperature and the state(s) of the naphthalene
  are recorded at half-minute intervals until the
  temperature of the naphthalene reaches 90C.

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Changes in states of matter
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Changes in states of matter

•  Procedure
• 1. The boiling tube in section A is removed from
  the water bath. The outer surface of the boiling
  tube is dried and immediately it is put in a
  conical flask, as shown in Figure 2.11. The
  naphthalene is stirred continuously.

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Changes in states of matter

•  Procedure
• 2 The temperature and state(s) of the
  naphthalene are recorded at 30-seconds interval
  until it reaches 60C.

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Changes in states of matter
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Changes in states of matter

• Results

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Changes in states of matter

• Discussion
• The heating graph of naphthalene
• 1. Notice that there is a certain part of the
  curve where is no change in temperature with time
  during heating.

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Changes in states of matter

• Discussion
• The heating graph of naphthalene
• 1. Notice that there is a certain part of the
  curve where is no change in temperature with time
  during cooling. At this temperature, both solid
  and liquid are present. It is the melting point
  of naphthalene. Hence, the melting point of
  naphthalene is 80.0C.

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Changes in states of matter

• Discussion
• The heating graph of naphthalene
• (a) At point A, naphthalene exists as solid.

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Changes in states of matter

• Discussion
• The heating graph of naphthalene
• (b) When the solid is heated, heat energy is
  absorbed. This causes the particles to gain
  kinetic energy and vibrate faster. The
  temperature increases from point A to point B.

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The cooling graph of naphthalene

• (c) At point B, solid naphthalene begins to
  melt. During the melting process, the temperature
  of naphthalene does not rise even though heating
  continues. The temperature remains constant
  because the heat energy absorbed by the particles
  is used to overcome the forces between particles
  so that the solid can turn into a liquid. At this
  temperature, both solid and liquid are present.

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Changes in states of matter

• (d) At point C, all the solid naphthalene has
  melted.

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Changes in states of matter

• (e) From point C to point D, the particles in
  liquid naphthalene absorb heat energy and move
  faster. The temperature increases from point C to
  point D.

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The cooling graph of naphthalene

• Discussion
• 2. Notice that there is a certain part of the
  curve where is no change in temperature with time
  during cooling.

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The cooling graph of naphthalene

• Discussion
• 2. Notice that there is a certain part of the
  curve where is no change in temperature with time
  during cooling. At this temperature, both solid
  and liquid are present. It is the freezing point
  of naphthalene. Hence, the freezing point of
  naphthalene is 80.0C.

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The cooling graph of naphthalene

• Discussion
• (a) At point M, naphthalene exists as liquid.

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The cooling graph of naphthalene

• Discussion
• (b) When the liquid is cooled, the particles in
  the liquid lose their kinetic energy. They move
  slower as the temperature decreases from point M
  to point N.

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The cooling graph of naphthalene

• Discussion
• (c) At point N, liquid naphthalene begins to
  freeze. During the freezing process, the
  temperature of naphthalene remains constant
  because the heat loss to the surroundings is
  balanced by the heat energy given off during
  freezing. At this temperature, both solid and
  liquid are present.

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The cooling graph of naphthalene

• Discussion
• (d) At point O, all the liquid naphthalene has
  frozen.

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The cooling graph of naphthalene

• Discussion
• (e) From point O to point P, the particles in
  solid naphthalene release heat energy and vibrate
  slower. The temperature decreases from point O to
  point P.

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Inter-conversion of States of Matter and Kinetic
Theory of Matter

• 3. During the heating of naphthalene,
• (a) a water bath is used instead of direct
  heating with a Bunsen flame. This is to ensure
  that the naphthalene is heated evenly.
  Furthermore, the naphthalene is flammable.  

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Inter-conversion of States of Matter and Kinetic
Theory of Matter

• 3. During the heating of naphthalene,
• (b) the naphthalene is stirred continuously to
  ensure an even heating.

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Inter-conversion of States of Matter and Kinetic
Theory of Matter

• Discussion
• 4. During the cooling of naphthalene,
• (a) the boiling tube containing the liquid
  naphthalene is placed in a conical flask. The air
  trapped in the conical flask is a poor conductor
  of heat. This helps to minimise the heat loss to
  the surroundings which may affect the accuracy of
  the freezing point obtained.

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Inter-conversion of States of Matter and Kinetic
Theory of Matter

• Discussion
• 4. During the cooling of naphthalene,
• (b) the naphthalene is stirred continuously to
  avoid supercooling. Supercooling is a condition
  in which the temperature of a cooling liquid
  drops below its normal freezing point, without
  the appearance of a solid.

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Inter-conversion of States of Matter and Kinetic
Theory of Matter

• Discussion
• 5. A water bath is used in this experiment
  because the melting point of naphthalene is below
  100C, the maximum temperature that can be
  attained by the water bath. For solids with
  melting points above 100C, a liquid with a
  higher boiling point than water such as oil must
  be used.

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Inter-conversion of States of Matter and Kinetic
Theory of Matter

• Conclusion
• The temperature of naphthalene increases when the
  solid is heated and it decreases when liquid
  naphthalene is cooled down. The melting and
  freezing points are the same, that is 80C.