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Chapter 9 - The Gaseous State Just as we can understand...

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The Gaseous State Just as we can understand structure and bonding from a molecular point of view, so we can also understand the properties of matter from a molecular perspective. This is the essence of the kinetic molecular theory of matter The connection between microscopic structure and macroscopic properties is termed statistical mechanics and pervades all aspects of science from chemistry to biology to integrated circuits. To understand how macroscopic properties arise from the structure and interactions of molecules it is easiest to start in the gas phase because: The densities of gases are much lower than solids and liquids and this means that the interactions between molecules can be simplified as they are on average a long way from each other
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Air (Best Known Gas)
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Pressure and Temperature Dependence At sufficiently low densities, all gases behave in the same way. This is a consequence of the fact that under these conditions the forces between molecules are relatively unimportant and thus each gas behaves much like another. This allows us to generalize their properties. The volume of a gas represents the amount of space occupied The pressure exerted by the gas is defined by the force exerted per unit area Pressure = Force/Area Gas
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Units of Pressure Are Varied
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PV = Constant In the 17th century the English scientist Robert Boyle noticed that if he compressed a gas by increasing the pressure that the volume would contract in such a way that the product of the pressure and volume remained constant: PV = Constant (Boyle’s Law) Increase Pressure
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PV = Constant (C) The value of the constant C was also found to depend on the temperature and the amount of gas in the container (i.e. the number of moles, n) There are a number of ways to demonstrate the validity of Boyle’s law graphically
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The Ideal Gas Law For a fixed pressure and amount of gas it has been observed that Volume of Gas (V)  Temperature (T) Where Temperature is in Kelvin; T(K) = 273.15K + T(C) Since we also know from Boyle’s law that; PV = Constant e can combine these various relationships to deduce the ideal gas la PV = nRT R – universal constant – 0.08206 L atm mol-1 K-1 From Avogadro’s hypothesis we also know that Volume of Gas (V)  n (number of moles of gas in volume V)
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Using PV = nRT A balloon filled with He has a volume of 1.0 x 104L at 1.00atm and 30C (303K). What is the volume of the balloon when it rises to an altitude where the pressure is 0.60atm and the temperature is -20C (253K), assuming that the pressure inside and outside the balloon is the same.
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