8: Intermolecular Forces
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Questions and Answers

What type of atoms are primarily attracted to unbonded electrons on nearby N, O, or F?

  • Hydrogen (correct)
  • Ionic bonds
  • Polar molecules
  • Carbon

    • Hydrogen bonds are not significant in biological processes.

    False

    Why does H2O have an exceptionally high boiling temperature?

    Due to strong hydrogen bonding between water molecules.

    In solutions, ions are solvated by a ______ liquid.

    <p>polar</p> Signup and view all the answers

    Match the terms with their definitions:

    <p>Ion-Dipole Interactions = Attraction between ions and polar molecules Hydrogen Bonds = Attraction between hydrogen and electronegative atoms Solvation = Process of surrounding solute particles with solvent Boiling Temperature = Temperature at which a liquid becomes a gas</p> Signup and view all the answers

    Which of the following statements regarding polar molecules as solvents is correct?

    <p>Polar molecules can solvate both positive and negative ions by orientation.</p> Signup and view all the answers

    Water (H2O) is the only solvent that can solvate ions.

    <p>False</p> Signup and view all the answers

    What is the strength of the ion-dipole interaction in kJ/mol?

    <p>≈ 50 kJ/mol</p> Signup and view all the answers

    The strength of a covalent C-H bond is approximately __________ kJ/mol.

    <p>413</p> Signup and view all the answers

    Match the following types of intermolecular interactions with their approximate strength:

    <p>Ion-Dipole = ≈ 50 kJ/mol H-Bonding = &gt; ~25 kJ/mol Dipole-Dipole = &gt; ~10 kJ/mol Dispersion = Weaker than ~10 kJ/mol</p> Signup and view all the answers

    Which of the following topics will NOT be covered in Lecture 9?

    <p>Vapor Pressure</p> Signup and view all the answers

    The office hours are still being held this week.

    <p>False</p> Signup and view all the answers

    What are the three states of matter?

    <p>solid, liquid, vapor</p> Signup and view all the answers

    The chapter that covers intermolecular forces is Chapter ___

    <p>11</p> Signup and view all the answers

    Match the following chapters with their topics:

    <p>Chapter 11 = Liquids and Intermolecular Forces Chapter 13 = Properties of Solutions Chapter 7 = Chemical Bonding Chapter 8 = Molecular Geometry</p> Signup and view all the answers

    Which of the following is an example of a factor affecting solubility?

    <p>All of the above</p> Signup and view all the answers

    The octet rule is related to the arrangement of electrons in an atom.

    <p>True</p> Signup and view all the answers

    What will be due tomorrow before Exercise #8?

    <p>Problem Set 7</p> Signup and view all the answers

    What does surface tension represent?

    <p>Energy per unit area of a liquid surface</p> Signup and view all the answers

    Repulsive interactions occur when two molecules are in close proximity.

    <p>True</p> Signup and view all the answers

    What phenomenon is described by water walking insects?

    <p>Surface tension</p> Signup and view all the answers

    If intermolecular interactions are strong, only a __________ fraction of molecules can enter the gas phase.

    <p>tiny</p> Signup and view all the answers

    Match the properties of liquids with their descriptions:

    <p>Surface tension = Energy per unit area Viscosity = Resistance to flow Vapor pressure = Molecules entering gas phase Capillary rise = Liquid movement in narrow spaces</p> Signup and view all the answers

    Which of the following statements about vapor pressure is correct?

    <p>It refers to molecules escaping from a liquid into the gas phase.</p> Signup and view all the answers

    Strong intermolecular interactions lead to a larger fraction of molecules in the gas phase.

    <p>False</p> Signup and view all the answers

    What is the effect of viscosity on liquid flow?

    <p>It slows down the flow.</p> Signup and view all the answers

    What describes the loss of intermolecular interactions when a liquid changes to a gas?

    <p>All intermolecular interactions are lost</p> Signup and view all the answers

    Intermolecular interactions are significant during the solid to liquid phase transition.

    <p>True</p> Signup and view all the answers

    What is the molar heat capacity of liquid water?

    <p>75.3 J mol−1 K−1</p> Signup and view all the answers

    The phase diagram shows phase changes depending on _____ and _____ .

    <p>temperature, pressure</p> Signup and view all the answers

    Match the following phase transition processes to their corresponding enthalpy changes:

    <p>A to B = 0.953 kJ B to C = 6.01 kJ C to D = 7.53 kJ D to E = 40.6 kJ</p> Signup and view all the answers

    What is the critical point in a phase diagram?

    <p>The point beyond which no distinct liquid phase exists</p> Signup and view all the answers

    At the triple point, only two phases coexist.

    <p>False</p> Signup and view all the answers

    What is the total enthalpy change (∆H) for the entire process of heating water as described?

    <p>56.0 kJ</p> Signup and view all the answers

    What happens to the boiling point of water as elevation increases?

    <p>It decreases</p> Signup and view all the answers

    All phase changes require a change in temperature.

    <p>False</p> Signup and view all the answers

    What is the term for the point at which all three phases of a substance coexist?

    <p>Triple point</p> Signup and view all the answers

    The heat required to change a solid to a liquid at its melting point is known as the heat of ______.

    <p>fusion</p> Signup and view all the answers

    Match the following terms with their corresponding definitions:

    <p>Viscosity = Resistance of a liquid to flow Surface tension = Energy required to increase the surface area of a liquid Vapor pressure = Pressure exerted by a vapor in equilibrium with its liquid Clausius–Clapeyron equation = Relation between pressure and temperature of phase transitions</p> Signup and view all the answers

    Which of the following interactions is typically the weakest?

    <p>Van der Waals interactions</p> Signup and view all the answers

    Solid CO2 (dry ice) sublimates at pressures above 1 atm.

    <p>False</p> Signup and view all the answers

    What is the phenomenon called when liquid turns into vapor without boiling?

    <p>Evaporation</p> Signup and view all the answers

    Study Notes

    Lecture Announcements

    • Today's Topics: Brown Chapter 11, focusing on liquids and intermolecular forces, including molecular comparisons of gas, liquid, and solids. Specific sections covered include intermolecular forces, properties of liquids, phase changes, and phase diagrams.
    • Problem Set 7: Due the following day. Submit on Moodle.
    • Problem Set 8: Posted on Moodle, due before Exercise 9 next week.
    • Study Center: Weekly sessions Wednesdays 6:00 PM to 8:00 PM in ETA F5.
    • Office Hours: No office hours this week.

    Lecture 9: Next Week's Topics

    • Topic: Chapter 13 of Brown, focusing on properties of solutions.
    • Sections: The solution process, saturated solutions, solubility, factors affecting solubility, expressing solution concentration, and colligative properties.

    Review of Lecture 7

    • Topic: Chemical bonding and molecular shapes.
    • Key Concepts: Basics of chemical bonding including ionic, covalent, and metallic bonds, Lewis symbols, octet rule. Multiple bonds, polarity, electronegativity, dipole moments, Lewis structures, resonance structures, exceptions to octet rules. Bonding enthalpies, strengths, bond lengths to covalent bonds, VSEPR model, electron domains.

    Lecture 2: Phases

    • Topic: States of matter: solid, liquid, and vapor, such as water.
    • Discussion Points: Physical properties of phases and reasons for phase changes.

    Explain Boiling Process

    • Topic: The boiling of liquids.

    Intermolecular Forces

    • Topic: Interactions between molecules.
    • Importance: Intermolecular forces affect many properties of interest to engineers, including phase changes, viscosity, wettability, and surface tension.
    • Examples Phase changes, Viscosity, Wettability, Lubrication, Surface Tension.
    • Engineer's Role: Understanding helps control effects to exploit them.

    General Properties of Phases

    • Topic: Defining properties that distinguish between phases (solid, liquid, gas).
    • Comparison Table: Properties including whether they fill containers, take the shape of a container, if they flow, closeness of molecules, ordering of molecules, and compressibility, are listed by phase.
    • Explanation: Differences in properties explained by intermolecular interactions.

    Ek versus Eint

    • Topic: Comparing kinetic energy of molecules (Ek) to potential energy due to intermolecular interactions (Eint)
    • Importance: The competition between Ek and Eint explains the transition between different physical states such as gas to liquid to solid with decreasing temperature.

    Intermolecular Interactions

    • Topic: Three types of interactions between neutral molecules.
    • A. Dispersion: Temporary fluctuations in electron distribution create temporary dipoles in neighbouring molecules, leading to attractive forces.
    • B. Dipole-Dipole: Permanent dipoles interact directly, forming stronger attractive forces.
    • C. Hydrogen Bonding: Very strong dipole-dipole interaction between a hydrogen atom covalently bonded to a highly electronegative atom (N, O, or F), and a lone pair of electrons on a nearby N, O, or F atom.

    Additional Notes

    • lon-Dipole: Important for solutions where ions are solvated by polar molecules (e.g., NaCl dissolving in water).
    • Strength of Interactions: Covalent bonds and hydrogen bonds are stronger than other types of intermolecular interactions.
    • Phase Diagrams: Important to understanding phase behaviour when plotted on a P vs. T graph. Including details on the phases (solid, liquid, and gas) and how pressures and temperatures affect phase transitions.

    Properties of Liquids

    • Vapor Pressure: The pressure exerted by the vapor in equilibrium with the liquid. Dependent on temperature. Molecules with sufficient kinetic energy can overcome intermolecular attractions and enter the vapor phase. The fraction of escaping molecules increases with increasing temperature.
    • Dynamic Equilibrium: Molecules are constantly leaving and returning to the liquid, and the rate of each is balanced.
    • Temperature Effects: If temperature increases more molecules go into the gas phase. If temperature decreases the tendency to return to the liquid phase increases.

    Phase Changes

    • Intermolecular Interactions: The strength of intermolecular forces determine the energy required for phase changes.
    • Enthalpy Change: The enthalpy change for each phase change can be determined by adding up those for the intermediate steps.

    Heating Curves

    • Example: Calculating heat needed to heat H₂O from -25°C to 125°C.
    • Determining enthalpy changes for different stages
    • Importance of vaporization in this process

    Phase Diagrams

    • Phase Transitions: Solid, liquid, and gas transitions are dependent on pressure and temperature.
    • Triple Point: Temperature and pressure at which solid, liquid, and gas phases coexist in equilibrium.
    • Critical Point: Condition at which the liquid and gas phases become indistinguishable.

    Boiling Process

    • Importance: Explain the boiling of water, and the effects of temperature and pressure.

    Aerogels

    • Property: A type of gel with a very low density (90-99.98% air by volume), made from silica.

    What We Learned

    • Detailed Summary of key concepts covered and their relevance in chemistry as per the provided text.

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    Lecture 8 - Chemistry - Liquids and Intermolecular Forces PDF

    Description

    Test your understanding of intermolecular forces and their significance in chemical interactions. This quiz covers key concepts such as hydrogen bonding, the properties of water, and solvation processes. Perfect for students studying chemistry and looking to reinforce their knowledge.

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