CHEM151Chapter 9

Chemistry (MasteringChemistry Series)

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11/17/2008 1 Gases 1 2 ` Earth is surrounded by a layer of gaseous molecules – the atmosphere – extending out to about 50 km. 3
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11/17/2008 2 ` Atmospheric Pressure : pressure exerted by Earth’s atmosphere; measured by a barometer ` Standard atmospheric pressure: column of mercury is 760 mm high at 0 o C at sea level 4 ` Pressure = force/area ` Units: N = kg·m/s 2 Pa = N/m 2 = kg/m·s 2 ` 1 atm = 760 torr = 760 mm Hg 1atm 1013kPa ` 1 atm = 101.3 kPa 5 ` Model of gases is Kinetic Molecular Theory 1. Tiny particles that move in random straight line motions. x low density and compressible 2. Volume of particles is negligible compared to the total volume of the gas x Xe at STP, only 0.025% of the volume is occupied by the atoms 6
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11/17/2008 3 3. Gas molecules move independently of one another x no intermolecular forces 4. Pressure arises from collisions of atoms/ molecules with walls of the container x no net energy loss from collisions x pressure is proportional to number of moles 5. Average kinetic energy (KE) is proportional to the temperature (Kelvin!) 7 ` Physical Behavior – P, V, T, & n (# of moles) Interdependent – All depend on each other ` Ideal Gas Law – Simple linear relationship between the variables (P, V, T, & n) ` Volume & Pressure Temp. & moles fixed V is inversely proportional to P ` The experiment: Air trapped in tube with mercury x Add more mercury (increase pressure), volume decreases
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11/17/2008 4 ` Volume & Temperature
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CHEM151Chapter 9 - 11/17/2008 Gases 1 2 Earth is surrounded...

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