Lecture 10

# Lecture 10 - From last class Ideal gas law from experiment...

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From last class… eal gas law from experiment Ideal gas law from experiment hyperbola (h * * 1 P = (h ρ Hg ) g P = (76cm * 13.6g/cm 3 ) * 980cm/s 2 P = 1*10 5 kg/m . s 2

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Charles’ Law All gases extrapolate to zero volume at the same T, if P is held constant 100 373 T (K) = 0 o C + 273 0 273 -273.15 0 This suggests gas volume would be < 0 at temperatures lower than -273.2 o C o CK 2 That is unphysical . This then suggests a new temperature scale (with an absolute zero)
Ideal Gas Law is example of an Equation of State PV= nRT State of gas is described by P, V, n and T you know any 3 of these you know the 4th If you know any 3 of these, you know the 4th Doesn’t matter what gas! Or what history! real gases approach ideal gas behavior at low P and high T Idea l gas law begins to fail at high P and low T, as liquid begin to condense from the gas Practical problem solving : 3 Real gases act largely in accordance with ideal gas law at 1atm and most temperatures Assume ideal gas behavior unless told otherwise

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Partial Pressure P t = n RT/V + n RT/V = P + P 4 partial pressure due to gas 1
Mixtures of Gases and Partial Pressure Dalton’s Law of Partial Pressure: For a mixture of gases in a container, the total pressure is the sum of pressures each gas would exert if it were alone. t = P + P + P +… partial pressure of gas 1 P tot P 1 P 2 P 3 P t = n RT/V + n RT/V + n RT/V +… tot 1 2 3 P tot = (n 1 + n 2 + n 3 +…) x (RT/V) P tot = n tot RT/V 5 Not surprising that total number of moles is the important thing given what we’ve learned so far

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Question: Chemicals X and Y (both gases) react to form the gas XY, but it takes a bit of time for the reaction to occur. Both X and Y are placed in a container with a piston (free to move), and you note the volume. As the reaction occurs, what happens to the volume of the container? a) Volume increases ) Volume tays the same b) Volume stays the same c) Volume decreases vary amount of gas pressure will be constant (set by external pressure) and record volume 6 PV= nRT
Partial Pressure and Mole Fraction Mole fraction ( χ ): ratio of number of moles of a given component in a mixture to the total number of moles in the mixture χ 1 = n 1 /n tot How does this relate to partial pressure? 11 1 1 (/ ) nP V R T P P χ == = = 1 12 1 2 ) ) tot tot n P V RT P V RT P P P + + * 7 P 1 = χ 1 P tot Partial pressure of a component is the mole fraction of that component times total pressure

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Ideal gas law is entirely macroscopic Kinetic Theory of Gases hat is the Microscopic molecular Basis for Gas Behavior ?
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## This note was uploaded on 11/03/2011 for the course MATH 1090 taught by Professor Greenwood during the Spring '08 term at MIT.

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Lecture 10 - From last class Ideal gas law from experiment...

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