Changes in the state of matter

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Malaysia SPM Chemistry, Form 4, Chapter 2, Structure of Atom
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Contents 1 Characteristic of Matter in Solid, Liquid and Gaseous State 2 The changes in the state of matter 2.1 Melting 2.2 Freezing 2.3 Vaporization 2.3.1 Evaporation 2.3.2 Boiling 2.4 condensation 2.5 sublimation 3 Melting Point, Freezing Point and Boiling Point 3.1 Melting Point 3.2 Freezing Point 3.3 Boiling Point 4 Physical State and Temperature 5 The Graph of the Heating Process 6 The Graph of the Cooling Process 6.1 Supercooling

[edit] Characteristic of Matter in Solid, Liquid and Gaseous State

Characteristic	Solid	Liquid	Gas
Image
Arrangement of Particles	Particles are arranged in an orderly manner and close to one another.	Particles are not arranged in order.	The space between particles is moderately large. The particles are very far apart and randomly arrange.
Movement of Particles	Particles vibrate at fixed positions.	Particles move randomly and slowly and sometimes will collide against each other.	The particles move randomly in all directions at great speed.
Force of Attraction between particles	very strong	Strong but weaker than in the solid state.	very weak
Ability to be compressed	Very difficult to be compressed because the particles are packed closely.	Not easily compressed because the particles are packed quite closely.	Easily compressed because the particles are very far apart.
Volume	Fixed	Fixed	Varied
Heat Energy content	Lowest Energy Content	Moderate energy content.	Highest energy content
Shape	Fixed	Follows the container	Fills the whole container

[edit] The changes in the state of matter

[edit] Melting

Definition Melting is the process where a solid changes to its liquid state at a certain temperature (called the melting point) and pressure when it is heated.

Notes

• When a solid is heated, the particles obtain energy and vibrate at a faster rate.
• As the temperature increases, the vibration of the particles increases until they reach the melting point where the particles obtain enough energy to overcome the forces that hold them in their fixed positions.The solid then changes into a liquid.
• During melting, the temperature remains constant. This is because the heat energy is taken in by the particles to overcome forces between them instead of being used to raise the temperature.
• The freezing and melting points of a pure substance are the same.

[edit] Freezing

Definition Freezing is the process where a liquid changes to its solid state at a certain temperature (called freezing point) and pressure when it is cooled.

Notes

• When a liquid is cooled, the temperature drops as heat energy is released to the surroundings.
• As heat energy is released, the kinetic energy of the particles in the liquid decreases, causing a slower movement of particles.
• The particles lose their energy and are pulled closer by the strong forces between the particles.
• As the temperature keep on dropping until it reach the freezing point, the liquid start changing into solid.
• The temperature stays constant while the liquid freezes because heat energy is released when the particles slow down to take up fixed and orderly positions in the solid.

[edit] Vaporization

Definition Vaporization, also called evaporation is the process whereby atoms or molecules in a liquid state gain sufficient energy to enter the gaseous state.

Boiling is the rapid vaporization of a liquid at a certain temperature (the boiling point) and pressure when heat is applied to it.

Notes

[edit] Evaporation

• Evaporation occurs below the boiling point of the liquid.
• The particles escape from the surface of the liquid to form gas.
• Evaporation differs from boiling in that it only takes place at the surface of the liquid and it is very slow.
• On the other hand, boiling takes place throughout the liquid and is very fast.
• Factors influencing rate of evaporation

1. Humidity of the air.
2. Temperature of the substance.
3. Flow rate of air.
4. Inter-molecular forces. The stronger the forces keeping the molecules together in the liquid or solid state the more energy that must be input in order to evaporate them.

• If conditions allow the formation of vapour bubbles within a liquid, the vaporization process is called boiling.

[edit] Boiling

• When a liquid is heated, the particles gain energy and move faster.
• As heat energy is keep on supplying to the liquid, the particles will eventually obtain enough energy to completely break the forces in between molecule.
• The liquid then changes into a gas and particles are now able to move freely and are far apart.
• The temperature at which this happens is called the boiling point.

The temperature remains constant during boiling because heat energy that is absorbed by the particles is used to break the forces holding them together.

[edit] condensation

Definition Condensation is the process by which a gas or vapor changes to liquid state at certain temperature and pressure when it is cooled.

Notes

• When a gas is cooled, the particles lose kinetic energy.
• As a result they move slower and this will cause the forces between them grow stronger.
• At this point, the gas changes into liquid.
• During condensation, heat is given out to the surroundings.
• Condensation can occur at or below the boiling point of the substance

[edit] sublimation

Definition Sublimation is a process of conversion of a substance from the solid to the vapour state without its becoming liquid.

Notes

• Some solids change directly into gas without becoming a liquid.
• This process is called sublimation.
• When heated, the particles of the solid gain enough energy to break the forces between them and move freely as a gas.
• When cooled, the gas changes straight back to solid.
• Examples of substances which sublime are solid carbon dioxide (dry ice), ammonium chloride and iodine.

Sublimation of Solid Carbon Dioxide (Dry Ice) Sublimation of Iodine (In this video, you can observe that when iodine is heated, it sublimes into purple gas. you can also observed that the purple gas reverse sublimes and forms black iodine on the test tube in the middle of the conical flask.) Other related video: http://www.youtube.com/watch?v=J8mDGwf-5x0

[edit] Melting Point, Freezing Point and Boiling Point

[edit] Melting Point

Melting Point Melting Point is the temperature at which the solid and liquid forms of a pure substance can exist in equilibrium.

[edit] Freezing Point

Freezing Point Freezing Point is the temperature at which a liquid becomes a solid.

[edit] Boiling Point

Boiling Point is the temperature at which the pressure exerted by the surroundings upon a liquid is equalled by the pressure exerted by the vapour of the liquid. Under this condition, addition of heat results in the transformation of the liquid into its vapour without raising the temperature.

[edit] Physical State and Temperature

The physical state of a substance at a certain temperature and pressure depends on the values of its melting and boiling points.

• A substance is in solid state if it exists at a temperature below its melting point.
• A substance is in liquid state if it exists at a temperature above its melting point but below its boiling point.
• A substance is in gaseous state if it exists at a temperature above its boiling point.

Change in heat and kinetic energy of particles

• The change in temperature will influences the kinetic energy or the speed of the motion of the particles.
• When a substance is heated, the kinetic energy of the particles in the substance increases. This causes the particles to move or vibrate faster.
• Likewise, when a substance is cooled, the kinetic energy of the particles in the substance decreases. This causes the particles to move or vibrate slower.
• The kinetic energy of the particles in a substance is directly proportional to the temperature of the substance.

[edit] The Graph of the Heating Process

The graph above shows the heating curve of naphthalene.

A	Naphthalene is in solid state at any temperature below its melting point. The particles are very closely packed together in an orderly manner. The forces between the particles are very strong. The particles can only vibrate at a fixed position.
A-B	As the naphthalene is heated, heat energy is converted to kinetic energy. Kinetic energy increases and the molecules vibrate faster about their fixed positions and the temperature increases.
B	Naphthalene is in solid state at any temperature below its melting point. The particles are very closely packed together in an orderly manner. The forces between the particles are very strong. The particles can only vibrate at a fixed position.
B-C	Naphthalene exists in both solid and liquid states. The temperature remains constant because the heat that supplied to naphthalene is used to overcome the forces of attraction that hold the particles together. The constant temperature is called the melting point. The heat energy that absorbed to overcome the intermolecular forces is named as the latent heat of fusion.
C	All the naphthalene has completely melted. Solid naphthalene has turned into liquid.
C-D	Naphthalene is in liquid state. As the liquid naphthalene is heated, the molecules gain more heat energy and the temperature continues to increase. The particles move faster and faster because their kinetic energy is increasing.
D	Naphthalene still exists in liquid state. Naphthalene molecules have received enough energy to overcome the forces of attraction between the particles in the liquid. Some of the naphthalene molecules start to move freely and liquid naphthalene begin to change into gas.
D-E	Naphthalene exists in both liquid and gaseous states. The temperature remains unchanged. The is because the heat energy absorbed is used to overcome the intermolecular forces between the particles of the liquid rather than increase the temperature of the liquid. This constant temperature is the boiling point.
E	All the naphthalene has turn into gas.
E-F	The gas particles continue to absorb more energy and move faster. The temperature increases as heating continues.

[edit] The Graph of the Cooling Process

P	The substance exists in gaseous state. The particles have very high energy and are moving randomly. The intermolecular forces between the particles are very weak and can be ignored.
P-Q	The substance is in gaseous state. The particles lose kinetic energy during cooling, the particles getting closer to each other and the temperature drops.
Q	The substance still exists as a gas. As the molecules are close enough, stronger forces of attraction result in forming of intermolecular bonds. The gas begins to condense and become liquid.
Q-R	The process of condensation going on. Stronger bonds form as gas changes into liquid. The substance exists in both gaseous and liquid states. The temperature remains unchanged. This is because the energy produced during the formation of bonds is equal to the heat energy released to the surroundings during cooling. This constant temperature is the boiling point. The heat energy that releases during this condensation process is called the latent heat of vaporization.
R	The substance exists only in liquid state as all the gas particles have condensed into liquid.
R-S	The substance exists as a liquid. As the temperature falls, the naphthalene molecules lose heat energy. Their movement shows down and they move closer to each other.
S	The substance still in liquid state. The particles have very little energy and begin to move closer towards one another as it starts to freeze into solid.
S-T	The liquid is changing into solid form. Molecules rearrange to form the molecular arrangement of a solid. The substance exists as both liquid and solid. The temperature remains constant until all the liquid changes to solid. This is because the energy released is the same as the energy lost to the surroundings during cooling. This constant temperature is the freezing point. The heat energy that releases during this freezing process is called the latent heat of fusion.
T	All the liquid freezes into solid. The particles are now closely packed in an orderly manner.
T-U	Once all the liquid has become solid, the temperature falls once again until it reaches room temperature. The substance is in the solid state here.
U	The substance reaches room temperature and remain at this temperature as long as the room temperature remain the same.

[edit] Supercooling

Super-cooling is the cooling of a liquid to below its freezing point but keeping it in liquid state. Supercooling is possible because of the lack of solid particles around which crystals can form.