CHEM12 Lecture - Ch. 13 Gases

States of Matter

  • Solid: Fixed volume and shape.

  • Liquid: Fixed volume, changes shape with container.

  • Gas: Indefinite volume, changes shape to fill container.

Behavior of Gases

  • Particles move rapidly and collide constantly.

  • Occupy a small part of total volume with little attraction/repulsion.

  • Collisions cause changes in direction and velocity.

  • Instruments to study properties include movable pistons, valves, thermometers, and pressure gauges.

Compressibility of Gases

  • Gases are compressible due to large empty spaces between molecules.

  • Volume decreases with an increase in pressure or decrease in temperature.

  • Liquids and solids are not compressible (fixed volume).

Pressure of Gases

  • Pressure results from collisions of gas particles with surrounding surfaces.

  • Pressure formula: Pressure = Force / Area.

Measurement of Atmospheric Pressure

  • Barometer measures atmospheric pressure.

  • Why Mercury?: It provides precision (760 mm = 29.92 in).

  • Invented by Evangelista Torricelli.

Units of Pressure

  • 1 atm = average pressure at sea level (0 °C).

  • 1 Pascal (Pa) = 1 Newton/m².

  • Conversion Factors:

    • 1 atm = 101,325 Pa = 101.325 kPa = 760 mm Hg = 760 torr = 14.7 psi = 29.92 in Hg.

Gas Laws Overview

  • Relationships between Pressure (P), Volume (V), Temperature (T), and number of moles (n).

  • Units: P (atm), V (L), T (Kelvin), n (mol).

Boyle’s Law

  • Relationship between Pressure and Volume at constant temperature and moles:

    • Formula: V ∝ 1/P --> P1V1 = P2V2.

Charles’s Law

  • Relationship between Volume and Temperature at constant pressure and moles:

    • Formula: V ∝ T --> V1/T1 = V2/T2.

Combined Gas Law

  • Combines Boyle’s and Charles’s Laws:

    • Formula: P1V1/T1 = P2V2/T2.

Avogadro’s Law

  • Relationship between volume and number of moles at constant temperature and pressure:

    • Formula: V ∝ n --> V1/n1 = V2/n2.

Gas Law Equations

  • Important for exams; know when to use each equation and practice solving for variables.

Ideal Gas Law

  • Formula: PV = nRT,

  • Where R = 0.0821 L·atm/(mol·K).

Standard Temperature and Pressure (STP)

  • Temperature = 273 K, Pressure = 1 atm.

  • Molar Volume of gas at STP: 1 mol = 22.4 L.

Stoichiometry and Gas Laws

  • Calculate moles from volume using P; apply in stoichiometric calculations.

Exercises and Examples

  • Example problems involve gas laws and conversions; practice using law equations.

  • Find theoretical yields based on gas behaviors and STP conditions.