Saturday, July 14, 2012

Heating or Cooling naphthalene

heating/cooling process (of naphthelene/acetamide)..EXP!!!

previous knowledge :::





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


Freezing PointFreezing Point Freezing Point is the temperature at which a liquid becomes a solid.
Boiling PointBoiling 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.
** make sure u know how to carry out the heating and cooling experiment for napthalene



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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.


DNaphthalene 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 gashave 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-ENaphthalene 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.


EAll the naphthalene has turn into gas.


E-FThe gas particles continue to absorb more energy and move faster.
The temperature increases as heating continues.



The Graph of the Cooling Process






PThe 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.

RThe substance exists only in liquid state as all the gas particles have condensed into liquid.

R-SThe 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.

TAll 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




Supercooling
** may b some of u still blu abt supercooling.... the most easier to show u s/cooling is ice...u put some water into the freezer, after 20min, it seems oredi freeze, but if press it with yo finger, the upper layer of ice will break, inside still remain water... this is what we call supercooling.

supercooling occur bcos the cooling temperature is not uniform. to avoid this , the boiling tube which is placed in the conical flask must continuously stirredthroughout the cooling process.

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