2.1b inter molecule

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.


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

MeltingWhen a solid is heated, the particles in the solid gain kinetic energy and vibrate more vigorously.



MeltingWhen 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.


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

MeltingWhen 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.


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

MeltingThe 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.



FreezingWhen a liquid is cooled, the particles in the liquid lose energy and move slower.



FreezingWhen 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.



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.



BoilingWhen 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.



BoilingThe 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.



CondensationWhen 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.



CondensationEventually, 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.



SublimationSublimation 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).

Experiment 2.2 To determine the melting and freezing points of naphthalene.Aim: To determine the melting and freezing points of naphthaleneChanges in states of matter


Experiment 2.2 To determine the melting and freezing points of naphthalene.MaterialsNaphthalene powder, water.


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


Procedure1. A boiling tube is filled with naphthalene to a depth of 3 cm and a thermometer is put into it.

Changes in states of matterProcedure2. 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.

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

Procedure3. The water is heated and the naphthalene is stirred slowly with the thermometer.


Procedure4. 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.


Procedure1. 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.


Procedure2 The temperature and state(s) of the naphthalene are recorded at 30-seconds interval until it reaches 60C.


Results


DiscussionThe heating graph of naphthalene1.Notice that there is a certain part of the curve where is no change in temperature with time during heating.


DiscussionThe heating graph of naphthalene1.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.


DiscussionThe heating graph of naphthalene(a) At point A, naphthalene exists as solid.


DiscussionThe 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.

(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.The cooling graph of naphthalene


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


(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.

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.


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.


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


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.


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.


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


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.


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.


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


Discussion4.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.


Discussion4.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.


Discussion5.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.


ConclusionThe 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.

2.1b inter molecule

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