# thankyou

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Science-Technology

Published on November 11, 2008

Author: anil_fury

Source: authorstream.com

Slide 1: chemistry This project is done by P5group Welcome Slide 2: OUR TOPIC IS Slide 4: The critical temperature, Tc, of a material is the temperature above which distinct liquid and gas phases do not exist. As the critical temperature is approached, the properties of the gas and liquid phases become the same resulting in only one phase: the supercritical fluid. Above the critical temperature a liquid cannot be formed by an increase in pressure, but with enough pressure a solid may be formed. Tc=8a/27Rb MICROSCOPIC VIEW OF A LIQUID : MICROSCOPIC VIEW OF A LIQUID Slide 6: CRITICALPRESSURE(PC): It is defined as minimum pressure applied on 1 mole of gas placed at a critical temperature,to just liquefy the gas Pc=a/27b2 Slide 7: Critical volume(Vc): The volume occupied by 1 mole of a gas under critical conditions is known as critical volume Vc=3b Slide 8: The vanderwalls equation (p+a/V2)(v-b)=Rt Critical constant equations Zc=Pcvc/Rt=a/(27b2)(3b)/r(8a/27rb)=0.375 Slide 9: Andrews' concept of critical temperature soon led to a breakthrough in the liquefaction of the so-called permanent gases. To reach temperatures low enough to liquefy these gases, two scientists independently came up with the idea of using a "cascade" process that reduces temperature step by step. In this method, one liquefied gas is used to cool a second gas that has a lower critical temperature; then the second gas, when liquefied, is used to cool another gas with an even lower critical temperature; and so on. Slide 10: the Joule–Thomson effect or Joule–Kelvin effect or Kelvin–Joule effect describes the temperature change of a gas or liquid when it is forced through a valve or porous plug while kept insulated so that no heat is exchanged with the environment.[1][2][3] This procedure is called a throttling process or Joule-Thomson process.[4] At room temperature, all gases except hydrogen, helium and neon cool upon expansion by the Joule-Thomson process.[5][6] The effect is named for James Prescott Joule and William Thomson, 1st Baron Kelvin who discovered it in 1852 following earlier work by Joule on Joule expansion, in which a gas undergoes free expansion in a vacuum Slide 12: Von Linde also developed more economical methods of separating the liquid oxygen and liquid nitrogen, which both found many practical uses in research and industry. Incandescent light bulbs filled with nitrogen, for example, lasted longer than earlier bulbs that used a vacuum instead of a filler gas. Liquid nitrogen is also quite useful for instantaneous freezing. In biological research, liquid nitrogen is used to freeze blood cells, sperm, tissues, and even whole small organisms. When frozen, the cells stop normal activities, allowing scientists to examine a "freeze-frame" of cellular life. Quiz : Quiz The Joule Thompson coefficient is zero at? A gas can be liquefied at? A gas that is heated up during joule Thompson effect at ordinary temperature? 1)o2 2)co2 3)h2 4)so2 A gas X causes heating effect when allowed to expand why? The critical temperature of a substance is defined as? The cooling caused by the expansion of a compressed gas below its inversion its temperature without doing external work is called as? Quiz answers : Quiz answers Inversion temperature Below its critical temperature H2 The Inversion temperature of the gas is very low The temperature above which a substance can exist only as a gas Joule thompson effect

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May 28, 2018

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