Kinetic Particle Theory


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Kinetic Particle Theory

  1. 1. IntroductionAll substances are matter. This includes the air, sea, Earth, all living creaturesand even the Sun and Stars.Matter is anything that has mass and takes upspace.There are three forms of matter solid, liquid,gas. These three forms are called states ofmatter.Particle TheorySolid.Particles in solid are held tightly and packed fairly closetogether - they are strongly attracted to each other..Particles are in fixed positions but they do vibrate.Liquid. Particles are fairly close together with some attractionbetween them..Particles are able to move around in all directions butmovement is limited by attractions between particles.Gas.Particles have little attraction between them.. Particles are free to move in all directions and collidewith each other and with the walls of a container and arewidely spaced out.
  2. 2. Properties of matterSolids Have a definite shape. Maintain that shape. Are difficult to compress as the particles are already packed closely together. Are often dense as there are many particles packed closely together.Liquids Do not have a definite shape. Flow and fill the bottom of a container. They maintain the same volume unless the temperature changes. Are difficult to compress because there are quite a lot of particles in a small volume. Are often dense because there are quite a lot of particles in a small volume.Gases Do not have a definite shape. Expand to fill any container. Are easily compressed because there are only a few particles in a large volume. Are often low density as there are not many particles in a large space.
  3. 3. Inter conversion of states of matterMelting In a solid the strong attractions between the particles hold them tightly packedtogether. Even though they are vibrating this is not enough to disrupt the structure.When a solid is heated the particles gain energyand start to vibrate faster and faster. Initially thestructure is gradually weakened which has theeffect of expanding the solid. Further heatingprovides more energy until the particles start tobreak free of the structure. Although the particlesare still loosely connected they are able to move around. At this point the solid ismelting to form a liquid. The particles in the liquid are the same as in the solid butthey have more energy. To melt a solid energy is required to overcome theattractions between the particles and allow them to pull them apart. The energy isprovided when the solid is heated up. The temperature at which something melts iscalled its "melting point" or melting temperature. At room temperature a material isa solid, liquid or gas depending on its melting temperature. Anything with a meltingtemperature higher than about 20oC is likely to be a solid under normal conditions.Boiling If a liquid is heated the particles are given more energy and move faster and fasterexpanding the liquid. The most energetic particles at the surface escape from thesurface of the liquid as a vapour as it gets warmer.Liquids evaporate faster as they heat up and moreparticles have enough energy to break away. Theparticles need energy to overcome the attractionsbetween them. As the liquid gets warmer moreparticles have sufficient energy to escape from theliquid. Eventually particles in the middle of the liquidform bubbles of gas in the liquid. At this point theliquid is boiling and turning to gas. The particles in thegas are the same as they were in the liquid they just have more energy. At normalatmospheric pressure all materials have a specific temperature at which boilingoccurs. This is called the "boiling point" or boiling temperature. As with the meltingpoint the boiling point of materials vary widely.
  4. 4. Evaporating Within a liquid some particles have more energy than other. These "moreenergetic particles" may have sufficient energy to escape from the surface of theliquid as gas or vapour. This process is called evaporation and the result ofevaporation is commonly observed when puddles or clothes dry. Evaporation takesplace at room temperature which is often wellbelow the boiling point of the liquid.Evaporation happens from the surface of theliquid. As the temperature increases the rate ofevaporation increases. Evaporation is alsoassisted by windy conditions which help toremove the vapour particles from the liquid so thatmore escape.Evaporation is a complex idea for children for anumber of reasons. The process involves the apparent disappearance of a liquidwhich makes the process difficult for them to understand. It is not easy to see thewater particles in the air. Also, evaporation occurs in a number of quite differingsituations - such as from a puddle or bowl of water where the amount of liquidobviously changes, to situations where the liquid is less obvious - such as clothesdrying or even those where there is no obvious liquid at all to start with - such asbread drying out. A further complication is that evaporation may be of a solvent froma solution e.g. water evaporating from salt water to leave salt. These situations arequite different yet all involve evaporation.
  5. 5. DiffusionDiffusion is one of several transport phenomena that occur in nature. Adistinguishing feature of diffusion is that it results in mixing or mass transportwithout requiring bulk motion. Thus, diffusion should not be confusedwith convection or advection, which is other transport mechanisms that usebulk motion to move particles from one place to another.From the atomistic point of view, diffusion is considered as a result ofthe random walk of the diffusing particles. In molecular diffusion, the movingmolecules are self propelled by thermal energy. Random walk of smallparticles in suspension in a fluid was discovered in 1827 by Robert Brown.The theory of the Brownian motion and the atomistic backgrounds of diffusionwere developed by Albert Einstein.Now, the concept of diffusion is widely used in science: in physics (particlediffusion), chemistry and biology, in sociology, economics and finance(diffusion of people, ideas and of price values). It appears every time, whenthe concept of random walk in ensembles of individuals is applicable.
  6. 6. Graham’s Law of DiffusionInter mixing of two or more gases to form a homogeneous mixture without anychemical change is called "DIFFUSION OF GASES". Diffusion is purely a physicalphenomenon. Gases diffuse very quickly due to large empty spaces amongmolecules. Different gases diffuse with different rates (velocities).The law stating that the rate of diffusion of a gas through a liquid (or thealveolar-capillary membrane) is directly proportional to its solubility coefficientand inversely proportional to the square root of its density.Grahams law is a quantitative relation between the density and rateof diffusion of gases.Mathematical Representation of the LawSince density a molecular mass, therefore, we can replace density d by Molecularmass M.
  7. 7. Effects of Pressure and Temperature on gasesIf the volume of the container is not fixed, increasing the temperature will causea gas to expand (increase the volume), and contract when cooled (decreasingthe volume). This would be the case for a gasinside a piston, or inside a rubber balloon.If the volume is fixed, then increasing thetemperature will increase the pressure, anddecreasing the temperature will decrease thepressure. This would be the case for a gas in aclosed solid container, like a canister or sealedmetal box.Increasing pressure will cause the gas to contract(reducing the volume), and decreasingthe pressure will cause the gas toexpand (increasing the volume).Again, this is if the volume is notfixed. If the volume is fixed, thenincreasing the pressure will increasethe temperature, and decreasing thepressure will decrease thetemperature.Gases can also be changed to a liquidor solid if the temperature is too lowor the pressure is too high. As anexample steam changes to a liquidwhen it touches a cold object, andnitrogen gas can be converted to liquid nitrogen by compressing it to very highpressures.