BEHAVIOR-OF-GAS-LIQUID-AND-SOLID

Behavior of Gas, Liquid, and Solid State Based on Kinetic Molecular Model

Ma. Christine O. Ruaza

Kinetic Molecular Model of Matter

  • All particles of matter are in constant random motion.

  • Kinetic energy (KE) exists in all states: solid, liquid, and gas.

  • Average kinetic energy is proportional to absolute temperature.

  • Particle speed order: solid < liquid < gas (with gas being more disordered).

  • Solid particles vibrate, albeit at a frequency undetectable to the naked eye.

Assumptions in Kinetic Molecular Model

  • Focus on gases (highest kinetic energy) with 5 assumptions:

    • Particles are in constant, random straight motion.

    • Volume of individual particles is negligible; separated by large distances.

    • Rapid and elastic collisions between particles and container walls.

    • No intermolecular forces exist between particles.

    • Total energy is conserved.

Properties of Gases and Liquids

  • Gases and liquids can flow, classified as fluids.

  • Experience intermolecular forces which influence their properties.

Intermolecular Forces

Dispersion (London) Forces

  • Present in non-polar substances, caused by electron oscillations.

  • Example: In argon gas, instantaneous dipoles occur due to electron distribution.

  • Stronger attractions at lower temperatures can cause particles to condense.

Dipole-dipole Forces

  • Attractive forces between polar molecules (uneven electron distribution).

  • Stronger than dispersion forces; attraction defined by Coulomb’s law.

  • Orientation in solids more orderly than in liquids.

Hydrogen Bond

  • Special strong dipole-dipole force,

    • Occurs with H bonded to N, O, or F.

    • Defined as H atom attracted to lone pair on N, O, or F.

Ion-Dipole Forces

  • Attraction between ions and nearby polar molecules.

  • Important in ionic compounds dissolving in water.

Summary of Intermolecular Forces

  • Identifying force types based on molecular characteristics:

    • London Forces: act on nonpolar molecules.

    • Dipole-dipole: act on polar molecules.

    • Hydrogen bonding: occurs in polar molecules with H.

    • Ion-dipole: links ions to polar molecules.

Properties of Liquids

  • Properties are dictated by intermolecular forces:

Surface Tension

  • Measure of elastic force at liquid's surface.

  • Caused by intermolecular forces; manifests like a "skin" on liquid's surface.

  • Water showcases high surface tension due to hydrogen bonding.

Viscosity

  • Measure of a liquid's resistance to flow, expressed in centipoise.

  • Temperature impacts viscosity: higher temperatures reduce viscosity.

  • Comparison example: Water (1 cp), Glycerol (high cp).

Vapor Pressure

  • Pressure in equilibrium between liquid and its gas phase.

  • Independent of liquid amount or surface area; increases with temperature.

  • Molecules must overcome intermolecular forces to vaporize.

Boiling Point

  • Temperature at which vapor pressure equals external pressure.

  • Example: Water's normal boiling point is 100 °C.

  • Related to molar heat of vaporization: Higher ΔHvap leads to higher boiling points.

Solids

  • Fixed mass, volume, shape; strong intermolecular forces; least intermolecular space.

  • Crystalline vs. Amorphous Solids:

Crystalline Solids

  • Particles in a regular repeating structure.

  • Low potential energy, thus more stability;

  • Examples: Iron, sodium chloride.

Amorphous Solids

  • Lack ordered internal structure;

  • Examples: Glass, rubber.

Differences between Crystalline and Amorphous Solids

  • Crystalline: periodic arrangement, specific melting point, symmetry in properties.

  • Amorphous: irregular arrangement, range of melting points, no definite symmetry.