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Some Gas Law Review. Units of pressure:. 1 Pa 1N/m 2 = (10 5 dyn)/(10 2 cm) 2 = 10 dyn/cm 2 1 torr = 1 mm Hg (Because P = mg / A = Vg / A = Ahg / A = gh ) 1 atm 760 torr = 101,325 Pa. Boyle’s Law:. PV = k (constant T, m ). Charles’ Law:.
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Some Gas Law Review Units of pressure: 1 Pa 1N/m2 = (105 dyn)/(102 cm)2 = 10 dyn/cm2 1 torr = 1 mm Hg (Because P = mg/A = Vg/A = Ahg/A = gh) 1 atm 760 torr = 101,325 Pa Boyle’s Law: PV = k (constant T, m) Charles’ Law: V/T = k (constant P, m) Combined Gas Law: Ideal Gas Law: PV = nRT R = 82.06 (cm3 atm)/(mole K) = 8.314 J/(mole K) = 1.987 cal/(mole K)
273 K Parts per thousand!
19 19 8 nm S M µ 5 .
The Barometric Formula Imagine a layer of gas of area, A, thickness dz and mass dm. The gas below pushes up with Fup = PA. The downward force on the layer is dm g plus the pressure from above, (P + dP)A. Since layer is in equilibrium, Fup=Fdown, PA = (P+dP)A + g dm, and dP = -(g/A)dm From the ideal gas law, PV = P(A dz) = (dm/M)RT, dm = (PMA/RT) dz and dP/P = -(Mg/RT) dz. Integrating (ignoring variation in T, g) gives: P = P0e-Mgz/RT From Ira N. Levine, “Physical Chemistry”