01 - Gas Intro and Boyles Law.ppt

Properties of Gases

  • No Attractive Forces: There are no attractive forces between gas molecules, causing them to behave independently.

  • Large Spaces: The spaces between gas molecules are substantial relative to the size of the molecules, making gases compressible.

  • Volume Occupation: Gases always occupy the total volume of their container.

  • Pressure and Volume Relationship: The smaller the volume of the container, the less room gas particles have to move, which leads to an increase in pressure.

Pressure

  • Definition: Pressure is defined as the force exerted by the gas on the walls of its container.

  • Measurement Units:

    • Newtons (N)

    • Pascals (Pa) where 1 Pa = 1 N/m²

    • Kilopascals (kPa) where 1 kPa = 1000 Pa

  • Pressure Conversion Units:

    • Pascal (Pa)

    • millimeters of mercury (mmHg) where 1 atm = 760 mmHg = 101,325 Pa

    • atmosphere (atm)

    • bar (1 bar = 100,000 Pa)

    • Torr (1 Torr = mmHg)

    • pound/sq inch (lb/in²) where 1 lb/in² = 51.7 mmHg

Converting Between Units of Pressure

  • Example Conversion from Atmospheres to kPa: Illustrates how to convert pressure values from atmospheres to kilopascals.

  • Example Conversion from kPa to Atmospheres: Demonstrates conversion techniques from kPa back to atmospheres.

  • Example Conversion from kPa to mmHg: Further provides a method for converting kPa to mmHg.

Kinetic Molecular Theory

  • Gas Behavior: Molecules are perpetually in random motion. Temperature influences molecular speed: higher temperatures increase molecular speed.

  • Molecular Speed Example: O₂ moves through air at approximately 400 m/s.

  • Types of Molecular Movement:

    • Rotation: Found in gases and liquids, and limited in solids.

    • Vibration: Occurs in gases, liquids, and minimal in solids.

    • Translation: Full movement from point A to point B, primarily in gases and partially in liquids.

Boyle's Law

  • Definition: Boyle's Law describes the relationship between pressure and volume in gases.

  • Pressure Explanation: Pressure is the force applied on a surface area. SI unit for pressure is Pascal (Pa), defined as 1 N on 1 m².

  • Pressure Reference Point: Atmospheric pressure at sea level is approximately 101.325 kPa or defined as 1 atm (standard pressure).

Volume Measurements

  • Volume Units: Volume is always measured in liters (L).

  • Inverse Relationship: As volume decreases, pressure increases; they are inversely proportional.

  • Statement of Boyle's Law: As pressure increases, volume decreases proportionally, given that temperature and amount of gas remain constant.

Example Problems

  • Example 1: Gas occupies 21 L at 222.9 kPa. Find the new volume at 628.1 kPa using p₁v₁ = p₂v₂. This demonstrates a decrease in volume with increased pressure.

  • Example 2: Oxygen (O₂) occupies 10.0 L at 104.7 kPa. Calculate the pressure at which the volume would increase to 14.5 L, illustrating pressure decrease with increased volume.

Special Conditions for Gas Measurements

  • Standard Ambient Temperature and Pressure (SATP): Defined as 25°C and 100 kPa; commonly used for periodic table measurements.

  • Standard Temperature and Pressure (STP): Defined as 0°C and 101.325 kPa.