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Lect_36_post - Schedule change Quiz 13 next week will be on...

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Schedule change: Quiz 13 next week will be on Thursday, April 21 (instead ofApril 19). Written homework is still due on Tuesday Group Problem 6 is on Tuesday Worksheet 15 on Thursday

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Lecture 36 Equations of state. The ideal gas. Kinetic model of a gas.
State variables State variables for a system: they characterize the system macroscopically at a given time. • Pressure • Temperature • Volume • Mass or moles Important: a system is in a thermal state that can be described by these variables when ALL of the system has uniform pressure, temperature, etc. Example: Gas in a tube whose ends are kept at different temperature is NOT in a thermal state. [ What s a mole? N A = 6.022 x 10 23 molecules/mol (Avogadro s number)]

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Equation of state Can be obtained: Empirically From statistical mechanics The equation of state relates the state variables.
The ideal gas An ideal gas is one whose molecules • are very small (point-like) • do not interact with one another This is true to very good approximation for any gas that is not in an extreme situation. The gas is NOT ideal if we: • have high density and high pressure • are near transition to liquid (or solid) • have very large molecules

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The ideal gas state equation pV nRT = n = number of moles J 8.31 mol K liter atm 0.082 mol K R = = Ideal gas constant Special cases (for constant mass or moles): Constant volume : Gay-Lussac s law Constant temperature : Boyle-Mariotte s law Constant pressure : Charles law = = = constant constant constant p T pV V T DEMO: Boyle- Mariotte Note: T here is always in Kelvins !
Example: Volume of ideal gas at STP V = nRT p = 1 mole ( ) 8.31 J mol K ! " # # \$ % & & 273.15 K ( ) 1.01 × 10 5 Pa = 0.0224 m 3 = 22.4 liters STP = Standard Temperature and Pressure = 0°C and 1 atm What is the volume of one mole of an ideal gas at STP?

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