Gases

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Gases Liquids

• Ch.12

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(12-1) Properties of Gases

• Fluids
• Low density
• Compressible
• Fill a container exert P equally in all
  directions
• Influenced by T

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Kinetic-Molecular Theory

• Explains behavior of gases
• 2 major assumptions
• Collisions are elastic
• V of individual gas molecules is negligible

KE is lost
KE is maintained
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Ideal Gas

• Describes the behavior of gases under most
  conditions
• High T low P gases act more ideal

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Kinetic Energy

• T of a gas determines the avg. KE of its
  particles
• KE ½ mv2
• Where, m mass, v speed

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Pressure

• Pressure (P) force (F)
• area (A)
• SI units
• F newtons (N)
• P pascal (Pa) 1 N/m2

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Standard Temp. Pressure

• STP std. conditions for a gas
• Temp. (T) 0 C (273 K)
• Pressure (P) 1 atm (101.325 kPa)
• See Table 12-1, p.428 for more P units

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Greenhouse Effect

• Inc. in the T of Earth caused by reflected solar
  radiation thats trapped in the atmosphere
• Inc. in greenhouse gases such as CO2 CFCs

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Free Radical

• Atom or molecule that has 1 or more unpaired e-
  is very reactive
• UV radiation breaks apart CFCs, making Cl
• Chain rxn self-sustaining rxn in which the
  product from 1 step acts as a reactant for the
  next step
• Cl O3 ? ClO O2 O
• ClO O ? Cl O2

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(12-2) The Gas Laws

• Symbols
• P pressure
• T temp in K
• V volume
• n of moles

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Boyles Law

• At constant T
• Inc. P, dec. V
• Dec. P, inc. V
• P1V1 P2V2

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Boyles Law Practice

• If the P exerted on a 300 mL sample of H2 gas at
  constant T is inc. from 0.500 atm to 0.750 atm,
  what will be the final V of the sample?
• List known
• V1 300 mL P1 0.500 atm
• V2 ? mL P2 0.750 atm

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Boyles Law Practice

• Write eq.
• P1V1 P2V2 ? V2 P1V1
• P2
• 3. Substitute solve
• V2 (0.500 atm)(300 mL) 200 mL
• 0.750 atm

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Daltons Law of Partial Ps

• Total P in a gas mixture is the sum of the
  partial Ps of the individual components
• Ptotal PA PB PC
• Where, Ptotal total P, PA partial P of A

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Daltons Law Practice

• A mixture of O2, N2, H2 gases exerts a total P
  of 278 kPa. If the partial Ps of O2 H2 are
  112 kPa 101 kPa respectively, what would be the
  partial P of the N2?
• List the known
• Ptotal 278 kPa PN2 ? kPa
• PO2 112 kPa PH2 101 kPa

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Daltons Law Practice

• List the eq. rearrange
• Ptotal PO2 PH2 PN2
• PN2 Ptotal - PO2 - PH2
• Substitute solve
• PN2 278 kPa 112 kPa 101 kPa 65 kPa

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Mole Fraction

• of moles of 1 component compared w/ the total
  of moles in the mixture
• Mole fraction (X) ____mol A___
• total mols
• To calc. partial P
• PA PTXA

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Mole Fraction Example

• The total P of a mixture of gases is 0.97 atm.
  The mole fraction for N2 is 0.78. Whats the
  partial P of N2?
• List the known
• Ptotal 0.97 atm XN2 0.78

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Mole Fraction Example

• Write the eq.
• PN2 Ptotal XN2
• Substitute solve
• PN2 (0.97 atm)(0.78)
• 0.76 atm

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Charles Law

• At constant P
• V inc., T inc.
• V dec., T dec.
• V1 V2
• T1 T2

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Charles Law Practice

• Gas in a balloon occupies 2.5 L at 300 K. The
  balloon is dipped into liquid N2 at 80 K. What V
  will the gas in the balloon occupy at this T?
• List known
• V1 2.5 L T1 300 K
• V2 ? L T2 80 K

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Charles Law Practice

• 2. Write eq.
• V1 V2 ? V2 V1T2
• T1 T2 T1
• 3. Substitute solve
• V2 (2.5 L)(80 K) 0.67 L
• (300 K)

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Pressure Temp.

• P inc. w/ inc. in T at constant V
• P1 P2
• T1 T2

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P T Practice

• Gas in a sealed can has a P of 3.00 atm at 25C.
  A warning says not to store the can in a place
  where the T will exceed 52C. What would the gas
  P in the can be at 52C?
• List known
• P1 3.00 atm T1 25C 298 K
• P2 ? atm T2 52C 325 K

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P T Practice

• 2. Write eq.
• P1 P2 ? P2 P1T2
• T1 T2 T1
• 3. Substitute solve
• P2 (3.00 atm)(325 K) 3.27 atm
• (298 K)

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Avogadros Law

• Vs of different gases under the same T Ps
  have the same of molecules
• V1 V2
• n1 n2

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Gay-Lussacs Law

• Law of Combining Volumes at constant T P,
  gases react in whole V proportions
• H2 Cl2 ? 2 HCl
• 1 V 1 V ? 2 V

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Effusion

• Motion of a gas through a small opening
• Diffusion gas particles disperse from areas of
  high to low conc.

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Grahams Law of Effusion

• At the same T P, 2 gases rates of effusion can
  be measured by
• ½ MAvA2 ½ MBvB2 or vA MB
• vB MA
• Where
• v speed of effusion (2 gases, A B)
• M molar mass

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Grahams Law Practice

• O2 has an avg. speed of 480 m/s at room T. On
  avg., how fast is SO3 traveling at the same T?
• List known
• vO2 480 m/s MO2 32 g/mol
• vSO3 ? m/s MSO3 80.07 g/mol

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Grahams Law Practice

• Write eq.
• vSO3 MO2 ? vSO3 vO2 MO2
• vO2 MSO3 MSO3
• 3. Substitute solve
• vSO3 (480 m/s) (32 g/mol)
• (80.07 g/mol)
• 300 m/s

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More Grahams Practice

• Compare the rate of effusion of H2O vapor w/ O2
  gas at the same T P.
• 1. List known
• MH2O 18.02 g/mol
• MO2 32 g/mol

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More Grahams Practice

• 2. Write eq.
• vH2O MO2
• vO2 MH2O
• 3. Substitute solve
• vH2O 32 g/mol 1.33
• vO2 18.02g/mol

H2O effuses 1.33X faster than O2
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(12-3) Ideal Gas Law

• PV nRT
• Where
• R 8.314 LkPa / molK or
• R 0.0821 Latm / molK

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Ideal Gas Law Practice

• Calculate the V of 1.00 mol of CO2 gas at STP.
• List known
• P 1.00 atm V ? L
• n 1.00 mol
• R 0.0821 Latm/molK
• T 273 K

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Ideal Gas Law Practice

• Write eq.
• PV nRT ? V nRT
• P
• Substitute solve
• V (1.00 mol)(0.0821 Latm/molK)(273 K)
• (1.00 atm)
• 22.4 L

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Combined Gas Law

• Moles remain constant, but other conditions
  change
• P1V1 P2V2
• T1 T2

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Combined Gas Law Practice

• A sample of CO2 gas occupies 45 L at 750 K 500
  kPa. Whats the V of this gas at STP?
• List known
• P1 500 kPa P2 101.325 kPa
• V1 45 L V2 ? L
• T1 750 K T2 273 K

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Combined Gas Law Practice

• Write eq.
• P1V1 P2V2 ? V2 P1V1T2
• T1 T2 T1P2
• 3. Substitute solve
• V2 (500 kPa)(45 L)(273 K)
• (750 K)(101.325 kPa)
• 81 L

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Gas Stoichiometry

• Gas Vs can be determined from mole ratios in
  bal. eqs.
• 3H2 N2 ? 2NH3
• 3 L 1 L 2 L
• 22 L N2 x 3 L H2 66 L H2
• 1 L N2

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(12-4) Changes of State

• Evaporation l ? g
• Condensation g ? l
• Sublimation s ? g

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Vapor Pressure

• P exerted by a vapor in equilibrium w/ its liquid
  state at a given T
• H2O(l) H2O(g)

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Phase Diagrams

• Shows Ts Ps at which a substance exists in
  different phases
• Phases are at equilibrium along the lines
• Phase substance has uniform composition
  properties

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Phase Diagrams (cont.)

• Normal bp boiling T at 1 atm
• Critical point T P above which the properties
  of vapor cant be distinguished from a liquid
• Supercritical fluids
• Triple point T P where 3 phases exist in equil.

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C.P.
N.B.P.
N.M.P.
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