[01.2] Solids and Liquids

PROPERTIES OF LIQUIDS AND SOLIDS

Introduction

  • Overview of properties of liquids and solids

Key Topics

  • Surface Tension

  • Viscosity

  • Vapor Pressure & Boiling Point

  • Molar Heat of Vaporization

  • Structure and Properties of Water

  • Types of Solids: Crystalline vs Amorphous

  • Types of Crystals: Ionic, Covalent, Molecular, Metallic

  • Phase Changes and Diagrams for Water and Carbon Dioxide

PROPERTIES OF LIQUIDS

Structure and Properties of Water

  • Central to understanding liquids

Molar Heat of Vaporization

  • Energy needed to convert a liquid to gas at boiling point

Vapor Pressure and Boiling Point

  • Vapor Pressure: Pressure exerted by vapor in equilibrium with its liquid

  • Boiling Point: Temperature at which vapor pressure equals atmospheric pressure

Viscosity

  • Definition: Resistance to flow of a fluid

  • Stronger intermolecular forces lead to higher viscosity

  • Examples of Viscosity:

    • Water: Low Viscosity

    • Olive Oil: Medium Viscosity

    • Honey: High Viscosity

Surface Tension

  • Definition: Energy required to increase surface area of a liquid

  • Influenced by intermolecular forces; higher forces lead to higher surface tension

  • Concept of Cohesion and Adhesion:

    • Cohesion refers to attraction between like molecules

    • Adhesion refers to attraction between unlike molecules

VAPOR PRESSURE

Definition

  • Pressure of vapor above a liquid (or solid) in a closed container when evaporation and condensation occur at equal rates.

Equilibrium Vapor Pressure

  • Established when condensation and evaporation rates reach equilibrium:

    • H2O (l) ⇔ H2O (g)

Evaporation

  • Process by which molecules escape from liquid to gas; a surface phenomenon.

  • Equilibrium leads to saturation vapor pressure.

Boiling Point

  • Temperature where saturated vapor pressure equals external pressure.

HEAT OF VAPORIZATION

Molar Heat of Vaporization (ΔHvap)

  • Energy needed to vaporize 1 mole of a liquid

  • Clausius-Clapeyron Equation is used to estimate vapor pressure at varying temperatures.

Example Calculations

  • Vapour pressure of water at different temperatures and the enthalpy of vaporization (40.7 kJ/mol at 373 K)

PROPERTIES OF SOLIDS

Types of Solids

  • Crystalline and Amorphous

    • Crystalline: Rigid, ordered, predictable positions of atoms/molecules.

    • Amorphous: Lack long-range order.

Types of Crystals

  • Ionic: Hard, brittle, high melting points (e.g., NaCl)

  • Covalent-Network: Strong covalent bonds, high melting points (e.g., diamond)

  • Molecular: Weak intermolecular forces, low melting points (e.g., sugar)

  • Metallic: Good conductors, range of hardness and melting points

Coordination Number in Crystalline Solids

  • Number of nearest neighbors surrounding an atom/ion in a solid.

  • Different types of unit cells (Simple Cubic, Body-Centered, Face-Centered) determine coordination numbers and densities.

Phase Changes

  • Transition from one state to another, including melting point and boiling point.

  • Critical Temperature and Pressure: Conditions above which distinct gas and liquid phases do not exist.

  • Phase diagrams illustrate conditions under which substances exist in solid, liquid, or gas states.

Example Effects of Pressure on Melting and Boiling Points

  • Increased pressure raises boiling point, while decreased pressure lowers melting point (e.g., Ice and water phase transitions)