Gases, Liquids and Solids

1
Chapter 8

• Gases, Liquids and Solids

2
States of Matter and Their Changes

• Matter exists in any of three phases, or states
• solid, liquid, or gas
• State depends on the attractive forces between
  particles, temperature, and pressure.
• Gas
• the attractive forces (potential energy) between
  particles are very weak compared to kinetic
  energy
• are far apart
• have almost no influence on one another.
• Liquid
• the attractive forces between particles are
  stronger

3
States of Matter and Their Changes

• Solid
• the attractive forces (potential energy) are much
  stronger than the kinetic energy
• atoms, molecules, or ions are held in a specific
  arrangement and can only wiggle around in place.

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States of Matter and Their Changes

• Phase change or change of state The
  transformation of a substance from one state to
  another.
• Melting point (mp) The temperature at which
  solid and liquid are in equilibrium.
• Boiling point (bp) The temperature at which
  liquid and gas are in equilibrium.
• Sublimation A process in which a solid changes
  directly to a gas.

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States of Matter and Their Changes
6
Gases and the Kinetic-Molecular Theory

• Gases can be compressed (keyboard cleaner)
• Gases exert pressure on what ever is around them
  (balloon, film canister)
• Gases expand into whatever volume is available
  (coke bottle and balloon)
• Gases mix completely with one another
• Gases are described in terms of their temperature
  and pressure, the volume occupied and the amount
  of gas present (gas properties)

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Kinetic Molecular Theory

• A gas is composed of molecules whose size is much
  smaller than the distance between them
• Gas molecules move randomly at various speeds and
  in every possible direction

8
Kinetic Molecular Theory

• Except when gas molecules collide, forces of
  attraction and repulsion between them are
  negligible
• When collisions between molecules occur, they are
  elastic
• The average kinetic energy of gas molecules is
  proportional to the absolute temperature (liquid
  N2 ballons, can, solar bag)
• Ek ½ (mass)(speed)2

9
Distribution of molecular speeds at three
temperatures.
10
Relationship between molar mass and molecular
speed.
11
Pressure

• Pressure
• Pressure force / area
• Force mass x acceleration
• Units of Pressure
• Atmosphere (atm)
• Torr
• Pascals (Pa)
• mmHg
• Pressure conversions
• 1 atm 1..01325 x 105 Pa
• 1 atm 760 torr
• 1 atm 760 mmHg

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Problem

• Convert these pressure values.
• 120 mmHg to atm
• 100 kPa to mmHg
• 270 torr to atm

13
The Gas Laws

• Gas properties
• Gases are described in terms of their temperature
  and pressure, the volume occupied and the amount
  of gas present (gas properties)
• Gas Laws can be derived using
• P, V, T, amount of Gas (n, mols)
• Kinetic Molecular Theory

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Boyles Law

• The Pressure-Volume Relationship Boyles Law
• The volume (V) of an ideal gas varies inversely
  with the applied pressure (P) when temperature
  (T) and the amount (n, moles) are constant
• PiVi PfVf

15
Problems

• A sample of nitrogen gas at 298 K and 745 torr
  has a volume of 37.42 L. What volume will it
  occupy if the pressure is increased to 894 torr
  at constant temperature?
• A)22.3 L
• B)31.2 L
• C)44.9 L
• D)112 L
• E)380 L

16
Problems

• A sample of carbon dioxide gas at 125C and 248
  torr occupies a volume of 275 L. What will the
  gas pressure be if the volume is increased to 321
  L at 125C?
• A)212 torr
• B)289 torr
• C)356 torr
• D)441 torr
• E)359 torr

17
Charless Law

• The Temperature-Volume Relationship Charless
  Law
• The volume (V) of an ideal gas varies directly
  with absolute temperature (T) when pressure (P)
  and amount (n) are constant.
• Vi / Ti Vf / Tf

18
Problems

• A sample container of carbon monoxide occupies a
  volume of 435 mL at a pressure of 785 torr and a
  temperature of 298 K. What would its temperature
  be if the volume were changed to 265 mL at a
  pressure of 785 torr?
• A)182 K
• B)298 K
• C)387 K
• D)489 K
• E)538 K

19
Problems

• A 0.850-mole sample of nitrous oxide, a gas used
  as an anesthetic by dentists, has a volume of
  20.46 L at 123C and 1.35 atm. What would be its
  volume at 468C and 1.35 atm?
• A)5.38 L
• B)10.9 L
• C)19.0 L
• D)38.3 L
• E)77.9 L

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Avogadros Law

• The Amount-Volume Relationship Avogadros Law
• The volume (V) of an ideal gas varies directly
  with amount (n) when temperature (T) and pressure
  (P) are constant
• V1 / n1 V2 / n2

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Combined Gas Law

• Combined Gas Law used when a specific amount
  of gas is exposed to two different conditions
• P1V1 / T1 P2V2 / T2

22
Problems

• A sample of propane, a component of LP gas, has a
  volume of 35.3 L at 315 K and 922 torr. What is
  its volume at STP?
• A)25.2 L
• B)30.6 L
• C)33.6 L
• D)37.1 L
• E)49.2 L

23
Problems

• Calculate the pressure of a helium sample at
  -207.3C and 768 mL if it exerts a pressure of
  175 kPa at 25.0C and 925 mL.
• A)32.1 kPa
• B)46.6 kPa
• C)657 kPa
• D)953 kPa
• E)not possible, since the pressure would have to
  be negative

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The Ideal Gas Law

• Boyles, Charless and Avogadros Laws can be
  combined to form the Ideal Gas Law
• PV nRT
• R ideal gas constant
• R 0.0826 atm L / mol K
• R 62.36 torr L / mol K
• R 8.314 J / mol K

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Problems

• A sample of nitrogen gas is confined to a 14.0 L
  container at 375 torr and 37.0C. How many moles
  of nitrogen are in the container?
• A)0.271 mol
• B)2.27 mol
• C)3.69 mo1
• D)206 mol
• E)227 mol

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Ideal Gas Law

• Various questions can be asked that relate gas
  laws to stoichiometry.

27
Problems

• A carbon dioxide sample weighing 44.0g occupies
  32.68 L at 65C and 645 torr. What is its volume
  at STP?
• A)22.4 L
• B)31.1 L
• C)34.3 L
• D)35.2 L
• E)47.7 L

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Problems

• A 250.0-mL sample of ammonia, NH3(g), exerts a
  pressure of 833 torr at 42.4C. What mass of
  ammonia is in the container?
• A)0.0787 g
• B)0.180 g
• C)8.04 g
• D)17.0 g
• E)59.8 g

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Ideal Gas Law

• The ideal gas law can be used to determine
  density if the molar mass of the gas is known or
  the molar mass if the mass of gas is known
• d m / V PM / RT
• Density increases with molar mass

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Problems

• 9What is the density of carbon dioxide gas at
  -25.2C and 98.0 kPa?
• A)0.232 g/L
• B)0.279 g/L
• C)0.994 g/L
• D)1.74 g/L
• E)2.09 g/L

31
Problems

• A flask with a volume of 3.16 L contains 9.33
  grams of an unknown gas at 32.0C and 1.00 atm.
  What is the molar mass of the gas?
• A)7.76 g/mol
• B)66.1 g/mol
• C)74.0 g/mol
• D)81.4 g/mol
• E)144 g/mol

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Problems

• Dr. I. M. A. Brightguy adds 0.1727 g of an
  unknown gas to a 125-mL flask. If Dr. B finds the
  pressure to be 736 torr at 20.0C, is the gas
  likely to be methane, CH4, nitrogen, N2, oxygen,
  O2, neon, Ne, or argon, Ar?
• A)CH4
• B)N2
• C)Ne
• D)Ar
• E)O2

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Partial Pressures and Daltons Law

• Daltons Law of Partial Pressures the total
  pressure exerted by a mixture of gases is the sum
  of the partial pressures of the individual gases
  in the mixture.
• Since all gases in a mixture occupy the same
  volume and are at the same temperature then the
  pressure is directly related to the moles of gas
• ntotal ngas1 ngas2 ..

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Partial Pressures and Daltons Law

• Placing ntotal into the ideal gas law
• PtotalV ntotalRT
• Ptotal ntotalRT / V
• Ptotal Pgas1 Pgas2 ..,

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Intermolecular Forces

• Intermolecular Forces
• Ionic compounds
• Ionic Force
• Covalent compounds
• Dipole-Dipole
• Hydrogen Bond
• London Forces

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Intermolecular Forces

• Hydrogen Bond Molecules containing NH, OH, or
  FH groups, and an electronegative O, N, or F.

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Intermolecular Forces

• DipoleDipole Between polar molecules.

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Intermolecular Forces

• London Dispersion Forces Attraction is due to
  instantaneous, temporary dipoles formed due to
  electron motions.

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Intermolecular Forces
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Liquids

• Properties
• Viscosity
• Viscosity is the measure of a liquids resistance
  to flow and is related to the ease with which
  molecules move around, and thus to the
  intermolecular forces.
• Vapor pressure

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Liquids

• Vapor Pressure The pressure exerted by gaseous
  molecules above a liquid.

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Solids

• Solids are divided into two categories
• Crystalline Possesses rigid and long-range
  order.
• Covalent Network Crystals
• Amorphous Lacks well-defined arrangement.

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Solids

• Sodium Chloride

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Solids

• Carbon