but meteorologists do not make this distinction. Theheat of sublimation equals the heat of fusion plus theheat of vaporization for a substance. The caloriesrequired for water to sublime are: 80 + 597.3 = 677.3, ifthe vapor has a temperature of 0°C.In the sublimation process of vapor passing directlyinto the solid form without going through the liquidphase, the calories released are the same as those for thesublimation of a solid to a gas. Sublimation of watervapor to ice frequently takes place in the atmospherewhen supercooled water vapor crystallizes directly intoice crystals and forms cirriform clouds.REVIEW QUESTIONSQ2-4. What are the two basic particles that make upthe composition of matter?Q2-5.What is the correct formula for density?Q2-6.What is fusion?GAS LAWSLEARNING OBJECTIVE: Recognize howpressure, temperature, and density affect theatmosphere and describe how the gas laws areapplied in meteorology.Since the atmosphere is a mixture of gases, itsbehaviorisgovernedbywell-definedlaws.Understanding the gas laws enables you to see that thebehavior of any gas depends upon the variations intemperature, pressure, and density.To assist in comparing different gases and inmeasuring changes of gases it is necessary to have astandard or constant to measure these changes against.The standard used for gases are: a pressure of 760millimetersofmercury(1,013.25mb)andatemperature of 0°C. These figures are sometimesreferred to as Standard Temperature and Pressure(STP).KINETIC THEORY OF GASESThe Kinetic theory of gases refers to the motions ofgases. Gases consist of molecules that have no inherenttendency to stay in one place as do the molecules of asolid. Instead, the molecules of gas, since they aresmaller than the space between them, are free to moveabout. The motion is in straight lines until the linescollide with each other or with other obstructions,making their overall motion random. When a gas isenclosed, its pressure depends on the number of timesthe molecules strike the surrounding walls. The numberof blows that the molecules strike per second againstthe walls remains constant as long as the temperatureand the volume remain constant.If the volume (the space occupied by the gas) isdecreased, the number of blows against the wall isincreased, thereby increasing the pressure if thetemperature remains constant. Temperature is ameasure of the molecular activity of the gas moleculesand a measure of the internal energy of a gas. When thetemperature is increased, there is a correspondingincrease in the speed of the molecules; they strike thewalls at a faster rate, thereby increasing the pressureprovided the volume remains constant.Therefore,there is a close relationship of volume, pressure, anddensity of gases.BOYLE’S LAWBoyle’s law states that the volume of a gas isinversely proportional to its pressure, provided thetemperature remains constant. This means that if thevolume is halved, the pressure is doubled. An exampleof Boyle’s law is a tire pump. As the volume of thepump’s cylinder is decreased by pushing the handledown, the pressure at the nozzle is increased. Anotherway of putting it is, as you increase the pressure in thecylinder by pushing down the handle, you also decreasethe volume of the cylinder.The formula for Boyle’s law is as follows:VP = V’P’V = initial volumeP = initial pressureV’ = new volumeP’ = new pressureFor example, assume 20 cm3 of gas has a pressureof 1,000 mb. If the pressure is increased to 1,015 mband the temperature remains constant, what will be thenew volume? Applying the formula, we haveV = 20 cm3P = 1000 mbV’ = Unknown in cm3P’ = 1015 mbV P = V’ P’20 1,000 = V’ 1,01520,000 = V’ 1,015V’ =200001015,,V’ = 19.71 cm32-8
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