KINETIC THEORY OF MATTER

 KINETIC THEORY OF MATTER

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Matter is made up of very tiny particles like atoms, molecules and ions.The kinetic theory if matter postrates that these particles are continually moving and so possess kinetic energy.

Meanwhile note that An increase in temperature causes an increase in the average kinetic energy of the particles also.

STATE OF MATTER

Matter exist as solid, liquid and gas. The fundamental difference between these three state of matter is the degree of movement of their particles.

SOlID STATE

Different types of solids are formed by different chemical combinations.

Also, The molecules, atoms, or even ions in these solids are closely packed, and they are held firmly together by forces of cohesion.

However the forces of cohesion may be electrovalent, covalent ,metallic,or the very weak van der Waal’s forces .The strength of any solid is determined by the type of bonds or forces binding the Crystal structure together.

Moreover the cohesive forces that is binding the particles of a solid are very strong enough to restrict their movement so that they can be able to held in fixed positions. These particles can only vibrate and rotate about their fixed positions buh they cannot translate , I.e. move from one place to another.

LIQUID STATE

The particles in a liquid are slightly further apart than those in a solid. However They have more kinetic energy and they no longer held in fixes positions. They can vibrate ,rotate, and even move from one place to another. Moreover the particles can also slide about randomly, note, they are still under the influence of the cohesive forces and even their movements are restricted. A liquid, therefore, still possesses a fixed volume but has no definite shape or form.

GASEOUS STATE

In gas ,the particles have much kinetic energy than those in a liquid. The cohesive forces in a gas are negligible and the Particles are free to move about in all directions at great speed and restricted only by the walls of the container. A gas has no definite shape :it occupies the whole volume of its container.

Matters into the gaseous state has different characteristics from that in the solid and liquid states. Thus ,the behavior of gases is expected to differ from that of solids and liquids. The gas law which explains the physical behavior of gases can be explained by the kinetic theory of gases. This theory describes the behavior of an ideal perfect Gas .it states the following:

The gas molecules move randomly in the straight lines, colliding with one another and with the walls of the various molecules differ widely and are constantly changing. The collision of the gas molecules bon the walls of the container constitute the gas pressure exerted in the container.

However the collision of gas molecules are well elastic. When two molecules collide ,their individual energies may change, and one may move faster while the other slows down, but no kinetic energy is converted to heat. When the molecules collide with the walls of the container, they rebounce like elastic balls without any loss of energy.

The actual volume which occupies by the gas molecules themselves is negligible relative to the volume of the container also. The gas molecules are also small in relation to the distances between them.

Meanwhile note, that the cohesive forces between the gas molecules are negligible.

The temperature of the gas is a measure of the average energy of the gas particles.

Pressure exerted by gas: The particles of a gas contained in a vessel move randomly at high speed ,often colliding with one another and with the walls of the containers. Each time a gaseous particles hits or collides with the wall of the vessel it exerts a very small force on it. Since the gas particles are numerous and evenly distributed, their collisions exert a constant force on the walls of the vessel .This force that the gaseous particles exert per a unit area of the wall is also known as gas pressure. It will be constant in every unit area of the walls of the vessel in which the gas is enclosed. Gas pressure is commonly measured in atmospheres (atm) or mm Hg. However Note that the S.I unit for measuring pressure is pascal(Pa), I.e. newtons per square metre(Nm-2).

The relationship between these units is: 1 ATM =mm Hg=101325 Nm-2.

CHANGE OF STATE

Note, that a substance can exist as a solid, liquid or even a gas. It is brought about by a change in temperature (heating and cooling). However, when a substance is heated , it’s particles acquire more kinetic energy. When cooled ,they become less energetic.

MELTING

When a solid us heated, the particles acquire more kinetic energy and vibrate more violently. A certain temperature called the melting point of the solid, the force of the vibration overcomes the binding forces and the crystalline structure collapses suddenly. The particles re no longer held in fixed positions, but instead are free to move about.

The presence of an impurity in the crystal will lower the melting point of a solid and may cause it to liquefy gradually instead of suddenly. In most cases e.g iodine, the molecules may break away from the Crystal and change directly into the vapour state when the solid is heated which is known as sublimation.

EVAPORATION: particles in a liquid are attracted by closely particles equally in all directions. Particles at the surface of a liquid body ,however ,are attracted only inwards and sideways by the neighbouring particles.

Meanwhile the surface of the liquid is level and is like a tightly_stretched skin. Note: that Such a liquid surface tends to prevent liquid molecules from escaping into the space above the liquid.

Remember In a sample of a given substance, some of the particles are more energetic than others. When such energetic particles comes in contact with a liquid surface, they can break away from the attractive forces of the other nearby liquid molecules.

However Since the evaporation results in escape of the energetic particles from the liquid body, it makes the average kinetic energy of the liquid to be lowered. Which results in a drop in temperature of the liquid body. However all, Evaporation occurs at every temperatures but, the rate of evaporation increases with the increase in temperature. Reason is that the average kinetic energy of a liquid is greater at a higher temperature, so there are more particles with sufficient energy to vaporize. Note that the amount of evaporation also depends on the type of liquid. Generally, the rate of evaporation is lower in electrovalent liquids than in covalent liquids. This is because the force of attraction is greater between the positive and negative ions in an electrovalent liquid than between simple neutral molecules in a covalent liquid. More energy is required for the particles in an electrovalent liquid to vaporize than for those in a covalent one. Thus , covalent liquids are said to be volatile.

VAPOUR PRESSURE

When a liquid evaporates in a closed container, the escaped particles will gradually accumulate in the space above the liquid. Here the Particles collide frequently with one another and with the walls of the vessel and consequently exert a pressure which is known as the vapour pressure. At the same time, some vapour molecules hit the liquid surface and re_enter the liquid (ie condense).

Condensation increases as the vapour pressure rises, i.e. as more and more liquid particles evaporate. Thus, two opposing forces are occurring in this system.

Liquid particles(forward reaction evaporate/reverse reaction condense)Vapour particles.

The vapour pressure continues to rise until a stage is reached at any given instant.

N/B: number of the particles condensing into the liquid while number of particles evaporating from the liquid.

BOILING

When a liquid is heated,the rate of evaporation increase . The saturated vapour pressure of the liquid also increases until a temperature is reached,at which it equals the prevailing atmospheric pressure. When this occurs ,bubbles of vapour form in the liquid and rise to the surface. The liquid is then said to boil and the temperature at which this happens is known as the boiling point of the liquid, at the prevailing atmospheric pressure. The boiling point increases or decreases with a rise OE fall in atmospheric pressure respectively. meanwhile It also increases in the presence of impurities.

FREEZING AND CONDENSATION

Heating causes melting and boiling, while cooling causes condensation and freezing. Condensation is a process whereby a vapour loses some of its kinetic energy to a colder body and changes into liquid state. This happens when a bottle of water is taken out of the refrigerator and placed on at stool at room temperature. Droplets of water can be seen on the outside surface of the bottle water. The vapour in the air around the bottle loses some of its energy to the bottle (cold body)and condenses as droplets of liquid water on the surface of the bottle.

When a liquid cools, it loses heat energy to it’s surrounding, causing its temperature to drop. If cooling is allowed to continue, the temperature of the liquid keeps on dropping until it reaches the freezing point of the liquid. At this temperature, the liquid changes into the same as its melting point.

LATENT HEATS OF FUSION AND EVAPORATION

During the process of melting, no temperature rise is observed even though heat energy is being supplied continuously. This is because the heat energy absorbed only performs the special function of weakening the cohesive forces which is not detectable by a thermometer. It is referred to as the latent(hidden) heat of fusion. Every solids has its own latent heat of fusion which depends on the strength of the cohesive forces .

The heat energy required to overcome the cohesive forces during boiling is known as the latent heat of vaporization. It is not detectable by a thermometer because this energy is not used to increase the temperature of this system but to break the cohesive bonds between the particles of the liquid.

DIFFUSION

It is stated that Diffusion explains movement of solute particles via a medium , from a areas of higher concentration to a a areas of a lower concentration. In other words ,the solute particles tend to move from a more crowded area to a less crowded erea.

Once the solute particles become evenly distributed throughput the medium,there will be no net diffusion in any particular direction.

Diffusion in gases: Diffusion in gases is fastest because gas particles have more kinetic energy than particles in liquids and solids. However the amount of diffusion of gases is affected by their densities.

Diffusion in liquids: Diffusion also takes place in liquids though it is much slower than in gases . This is because liquid particles have less kinetic energy and are more restricted j their movement due to the cohesive forces between the particles.

Diffusion in solids: Diffusion may also be observed in solids but the process is extremely slow.

Diffusion is fastest in gases. Their particles are far apart the cohesive forces between them are negligible. It is slowest I solids , where the particles are held in fixed positions by strong cohesive forces.

OSMOSIS

Osmosis is a special case of diffusion which involves the movement of Water molecules, through a semi_permeable membrane, from a region where they are in higher concentration to a region of lower concentration. Osmosis also indicates the movement of water molecules.

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