Gases, Liquids and Solids: Swimmers (and all Canadians who have been rescued by the Coast Guard!)...
Transcript of Gases, Liquids and Solids: Swimmers (and all Canadians who have been rescued by the Coast Guard!)...
Gases, Liquids and Solids:• Swimmers (and all Canadians who have been
rescued by the Coast Guard!) know that the human body is slightly less dense than water but rather more dense than air.
• Liquids and solids (high density) have small molar volumes. Gases have much larger molar volumes at “normal” temperatures and pressures. Gases are “easily” compressed!
Table 1Substance ( Phase ) Experimental Molar Volumes (L.mol-1) ( 00
C and 1.00 bar)
H2O(l) 0.01802
H2O(s) 0.01965 (less dense than H2O(l))
C2H5OH(l) 0.0584
NaCl(s) 0.0270
He(g) 22.72
H2(g) 22.72
N2(g) 22.70
CO2(g) 22.56
Table 2Substance ( Phase ) Densities ( g.L-1) at 00 C and 1.00 bar
H2O(l) 999.8
H2O(s) 917.0 Icebergs!
C2H5OH(l) 789 George Street.
NaCl(s) 2165
He(g) 0.176 Party Balloons!
H2(g) 0.0887
N2(g) 1.234
CO(g) 1.234 Life is too tough??
CO2(g) 1.951 Photosynthesis.
Condensed Phases and Gases at “Normal” Temperatures and Pressures • Condensed phases (solids and liquids) have
relatively small molar volumes and “high” densities.
• Gases have relatively high molar volumes and “low” densities
• Simple Explanation – in condensed phases molecules are “touching” each other – no “empty” space.
Gases at “Normal” Temperatures and Pressures
• Gases are mostly empty space – and are thus easily compressed. This is not true at very high P and low T. (Demonstration with dry ice!)
• Gases at low pressure can be condensed if subjected to a higher (external) pressure. Gases at high pressure will expand if the external pressure is reduced (propane barbecue).
• There are many(!) pressure units.
Pressure Units
• By definition: Pressure = Force/Area• “Old” units for P: lb.in-2, mm Hg or torr• Modern or SI pressure units• P = Force/Area = N/m2 = kg.m s-2/m2 = Pascal• Standard atmospheric pressure = 101.325 kPa• 101.325 kPa = 1.01325 x 105 Pa (usual metric
abbreviations)• We often measure atmospheric pressure using a
barometer containing Hg or another liquid.
The gaseous state of three halogens (group 17)Figure 6-1
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Liquid PressureFigure 6-3
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liquid pressure is directly proportional to the liquid density and the height of the liquid column
P (Pa) =
AF =
AW =
Ag x m =
Ag x V x =
Ag x h x A x = g x h x
Measurement of atmospheric pressure with a mercury barometer
Figure 6-4
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Standard Atmospheric Pressure 1.00 atm, 101.325 kPa, 1.01325 bar, 760 torr, ~760 mm Hg
Measurement of gas pressure with an open-end manometer
Figure 6-5
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Relationship between gas volume and pressure – Boyle’s Law
Figure 6-6
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PV = constantP 1V
6-2 Simple Gas Laws
Boyle’s Law:• The equation PV = constant is valid for a fixed
amount of a particular gas at a fixed temperature. One could take two points on the previous graph say (V1,P1) and (V2,P2) and write
• P1V1 = P2V2 = constant or just P1V1 = P2V2 • This expression can be used to predict, for
example, how the volume of a gas will change when the pressure is altered or….? We call this an initial state → final state problem.
Class Example – Boyle’s Law:• At a particular temperature and a pressure of
242 kPa a sample of argon gas Ar(g) has a volume of 3.87 L. What will be the gas volume if the pressure is reduced to 88.6 kPa? (Mention the trichotomy axiom?)