College Chemistry Ch5

General Chemistry Notes

Changes in State

  • Changes in state are physical changes.

  • Physical properties change during a change of physical state.

  • Focus on differences in physical properties among gases, liquids, and solids.

Physical Properties of Gases, Liquids, and Solids

  • Comparison of volume, shape, density, compressibility, particle motion, and intermolecular distance.

  • Gases expand to fill volume, liquids have fixed volume, and solids have fixed volume and shape.

  • Gases have low density, high compressibility, and particles that move freely.

The Gaseous State

  • Ideal gas concept involves measuring temperature, volume, pressure, and mass.

  • Gas laws relate number of moles, volume, temperature, and pressure.

  • Gas pressure results from particle collisions with container walls.

Kinetic Molecular Theory of Gases

  • Gases consist of small atoms or molecules in constant motion.

  • Gas particles behave independently with no attractive or repulsive forces.

  • Collisions between gas particles and container walls transfer energy.

Boyle’s Law

  • Volume of a gas varies inversely with pressure at constant temperature and moles.

  • Product of pressure and volume is a constant.

  • Used to calculate volume or pressure changes in gases.

Charles’s Law

  • Volume of a gas varies directly with absolute temperature at constant pressure and moles.

  • Ratio of volume and temperature is a constant.

  • Used to calculate volume changes with temperature variations.

Combined Gas Law

  • Combines Boyle’s and Charles’s laws for changes involving volume, pressure, and temperature.

  • Derived from a combination of Boyle’s law and Charles’s law.

  • Used to calculate volume changes with simultaneous variations in volume, pressure, and temperature.

Page 24

  • Practice problem with the Combined Gas Law

    • Calculate temperature change when gas is compressed

    • Initial: 0.50 L, 1.0 atm, 25°C

    • Final: 0.05 L, 5.0 atm

Page 25

  • Avogadro’s Law

    • Equal volumes of ideal gas contain same moles

    • Changes calculated using equation 5.1

  • Rewriting equation for Avogadro’s Law

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  • Using Avogadro’s Law

    • Example with CO moles and volume

    • 5.50 mol CO in 20.6 L, find volume for 16.5 mol CO

Page 27

  • Molar volume at STP

    • Volume occupied by 1 mol gas at STP

    • STP: T = 273 K, P = 1 atm

    • Molar volume of any gas at STP is 22.4 L

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  • Gas Densities

    • Density = mass / volume

    • Calculate density of 4.00 g He at STP

    • Molar volume of any gas at STP is 22.4 L

Page 29

  • Ideal Gas Law

    • Combination of Boyle’s, Charles’s, Avogadro’s laws

    • Ideal Gas Law equation: PV = nRT

Page 30

  • Ideal Gas Law Constant

    • R is ideal gas constant

    • R = 0.0821 L.Atm/mol.K

    • Units for P, V, n, T in equation

Page 31

  • Calculating Molar Volume

    • Demonstrating molar volume of O2 gas at STP

    • Using ideal gas law equation

Page 32

  • Practice with Ideal Gas Law

    • Finding volume of gas with given mass, temp, pressure

    • Finding mass of N2 for given volume, temp, pressure

Page 33

  • Dalton’s Law of Partial Pressures

    • Mixture of gases pressure sum

    • Equation for Dalton’s Law

Page 34

  • Dalton’s Law in Atmosphere

    • Total pressure = pressures of N2 and O2

    • Equation for Dalton’s Law in atmosphere

Page 35

  • Ideal Gases vs. Real Gases

    • Ideal gas model for gas behavior

    • Nonpolar gases behave more ideally

    • Polar gases have attractive forces

Page 36

  • Liquid State

    • Compressibility and Viscosity of liquids

    • Factors affecting viscosity

    • Viscosity decreases with temperature increase

Page 37

  • Surface Tension

    • Measure of attractive forces in liquid

    • Surfactant decreases surface tension

Page 38

  • Vapor Pressure of Liquid

    • Liquid and vapor coexistence

    • Kinetic theory and vapor pressure

Page 39

  • Temperature Dependence of Vapor Pressure

    • Molecular kinetic energy and temperature

    • High energy molecules escape liquid phase

Page 40

  • Movement From Gas to Liquid

    • Vapor phase molecules converting to liquid

    • Evaporation and condensation processes

Page 41

  • Equilibrium Between Liquid and Vapor

    • Equilibrium in evaporation and condensation

    • Vapor pressure definition

Page 42

  • Boiling Point

    • Vapor pressure equals atmospheric pressure

    • Normal boiling point at 1 atm

    • Boiling point variation with pressure and intermolecular forces

Page 43

  • Van der Waals Forces

    • Explaining liquid properties with intermolecular forces

    • Two types: Dipole-dipole and London dispersion forces

Page 44

  • Hydrogen Bonding

    • Special dipole-dipole attraction

    • Strong intermolecular attraction

    • Requirement for hydrogen bonding

Page 45

  • Examples of Hydrogen Bonding

    • Influence on biological systems

    • Examples: H2O, NH3, HF

Page 46

  • Solid State

    • Properties of solids

    • Fixed shape and volume

Page 47

  • Types of Crystalline Solids

    • Ionic, Covalent, Molecular solids

    • Characteristics and examples for each type

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  • Type of Crystalline Solids: Metallic Solids

    • Made up of metal atoms held together by metallic bonds

    • Metallic bonds formed by overlap of metal atomic orbitals

    • Regions of high electron density, very mobile and move freely

    • High conductivity

    • Examples include Ag (Silver) and Cu (Copper)

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  • Sublimation of Solids

    • Sublimation is the process of molecules in solid state converting directly to gaseous state

    • Example: Dry ice (solid carbon dioxide) converts directly to gas at