Absolute Zero and the Kelvin Scale

Absolute Zero and the Kelvin Scale

• Experiments show that when gas volume is plotted against temperature, lines extrapolate to -273.15 °C.
• -273.15 °C is interpreted as the theoretically lowest possible temperature, known as absolute zero.
• Lord Kelvin established the Kelvin scale in 1848, starting at absolute zero.
• A kelvin (K) has the same size as a degree Celsius (°C).
• Absolute zero is -273.15 °C, which equals 0 K.
• The freezing point of water is 0 °C, which equals 273.15 K.
• The boiling point of water is 100 °C, which equals 373.15 K.
• There are 273.15 kelvins between absolute zero and the freezing point of water.
• There are 100 kelvins between the freezing and boiling points of water.
• For Celsius temperature, t is often used; for Kelvin temperature, T is used.
• To convert Celsius to Kelvin: T = t + 273.15
• To convert Kelvin to Celsius: t = T - 273.15

Charles's Law

• The volume of a fixed amount of gas at constant pressure is directly proportional to its Kelvin temperature.
• When graphing volume vs. Celsius temperature, each line has a different y-intercept.
• When graphing volume vs. Kelvin temperature, all lines have a y-intercept of zero.
• Charles's Law is expressed as V₁/T₁ = V₂/T₂.
• The Kelvin scale simplifies the volume and temperature relationship with Charles's Law.

Charles's Law and Kinetic Molecular Theory

• The Kelvin temperature of a gas is directly proportional to the average kinetic energy of its molecules (Ek = 1/2 mv²).
• Increased temperature means faster-moving molecules, leading to more frequent and forceful collisions.
• If external pressure is constant and temperature increases, the gas expands.
• As volume increases, molecules travel farther, reducing collision frequency until internal and external pressures equalize.

Key Concepts

• Gases are compressible, have low density, are miscible, and expand with increasing temperature.
• Kinetic Molecular Theory explains gas behavior through the motion of gas particles.
• Absolute zero is the lowest possible temperature (-273.15 °C or 0 K).
• The Kelvin scale is a temperature scale based on absolute zero.
• Charles's Law is V₁/T₁ = V₂/T₂
• At constant pressure, volume is directly proportional to Kelvin temperature.