Properties of ideal gases

Properties of Gases

Introduction

  • Focus on three main properties of gases: pressure, volume, and temperature.

Pressure

  • Pressure is measured in Pascal (Pa), which is equivalent to Newton per square meter (N/m²).

    • Pascal is the SI unit for pressure.

  • Atmospheric pressure example:

    • Normal air pressure is approximately 100 kilopascals (kPa) or 100,000 Pa.

    • Car tire pressure: around 400 kPa, approximately 300 kPa above atmospheric pressure.

    • Oxygen in gas cylinders: about 14,000 kPa (14 MPa).

  • Important to convert pressure into Pascals for calculations.

Volume

  • Volume is measured in cubic meters (m³).

    • Example:

      • A refrigerator's interior is about 0.6 m³.

      • Caravan volume: approximately 15 m³.

  • Conversion examples:

    • 2 liters = 2 x 10^-3 m³ (1,000 liters in 1 m³).

    • 300 cm³ = 0.3 liters = 0.3 x 10^-3 m³ (1,000 cm³ in 1 liter).

  • Always convert to cubic meters before using in equations.

Temperature

  • Temperature in scientific contexts should be in Kelvin (K).

    • Steps for conversion:

      • To get Kelvin from degrees Celsius: add 273.

      • Examples:

        • Boiling water: 100°C = 373 K.

        • Melting ice: 0°C = 273 K.

        • Liquid nitrogen: -196°C = 77 K.

        • Bunsen burner flame: 1500°C = 1227 K.

  • Kelvin scale starts from absolute zero (0 K), the lowest possible temperature.

Ideal Gas Equation

  • The Ideal Gas Equation: PV = n k T

    • Where:

      • P = pressure (Pa)

      • V = volume (m³)

      • n = number of gas particles

      • k = Boltzmann's constant (usually provided)

      • T = temperature (K)

  • Rearranging the equation to find any variable:

    • Example for n: n = PV / kT.

Example Problems

  1. Finding Number of Particles:

    • Given data: Pressure = 8,000 kPa = 8,000,000 Pa

    • Volume = 15 L = 0.015 m³

    • Temperature = 20°C = 293 K

    • Use equation to calculate: n.

    • Result yields approximately 2.9 x 10²⁵ particles.

  2. Finding Temperature:

    • Given data: Pressure = 400 kPa = 400,000 Pa

    • Volume = 10 L = 0.01 m³

    • Particles = 9.6 x 10²³.

    • Rearranged equation gives: T.

    • Result is approximately 298 K or 25°C after conversion.

  3. Finding Volume:

    • Given data: Pressure = 100,000 Pa, Temperature = 291 K, number of particles calculated.

    • Use: V = n k T / P.

    • Calculate to find Volume as approximately 4.5 x 10^-3 m³.