10.1 Temperature and Heat

Temperature and heat are key players in thermodynamics. They describe how energy moves and changes in matter. Understanding these concepts helps us grasp everyday phenomena, from why ice melts to how our bodies regulate temperature.

This section dives into temperature scales, heat transfer, and phase changes. We'll explore how particles behave at different temperatures and learn about the energy involved when substances change state. These ideas form the foundation for understanding more complex thermodynamic processes.

Temperature and Thermal Energy

Fundamental Concepts of Temperature

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• Temperature measures the average kinetic energy of particles in a substance
• Thermal energy represents the total kinetic energy of all particles in a system
• Kinetic theory explains the behavior of particles in matter based on their motion
• Particles in solids vibrate, in liquids flow, and in gases move freely
• Higher temperature correlates with faster particle movement and increased thermal energy

Understanding Absolute Zero

• Absolute zero defines the lowest possible temperature (0 K or -273.15°C)
• At absolute zero, particles have minimal kinetic energy
• Reaching absolute zero remains theoretically impossible
• Scientists have achieved temperatures extremely close to absolute zero (nanokelvin range)
• Studying matter near absolute zero reveals unique quantum properties (superconductivity)

Temperature Scales

Celsius and Fahrenheit Scales

• Celsius scale uses water's freezing (0°C) and boiling (100°C) points as references
• Fahrenheit scale sets water's freezing at 32°F and boiling at 212°F
• Convert Celsius to Fahrenheit: $°F = (°C × 9/5) + 32$
• Convert Fahrenheit to Celsius: $°C = (°F - 32) × 5/9$
• Celsius widely used in scientific contexts and most countries
• Fahrenheit commonly used in the United States for everyday temperature measurements

The Kelvin Scale

• Kelvin scale starts at absolute zero (0 K)
• One Kelvin unit equals one Celsius degree in size
• Convert Celsius to Kelvin: $K = °C + 273.15$
• Convert Kelvin to Celsius: $°C = K - 273.15$
• Kelvin scale used in scientific calculations and thermodynamics
• Negative temperatures do not exist on the Kelvin scale

Heat and Its Effects

Heat Transfer and Capacity

• Heat flows from higher to lower temperature objects
• Heat transfer occurs through conduction, convection, and radiation
• Specific heat capacity measures energy required to raise temperature of 1 kg of substance by 1°C
• Water has a high specific heat capacity (4,186 J/kg·°C)
• Materials with high specific heat capacity (copper) heat up and cool down slowly

Latent Heat and Phase Changes

• Latent heat represents energy absorbed or released during phase changes
• Phase changes occur at constant temperature
• Melting (solid to liquid) and freezing (liquid to solid) involve latent heat of fusion
• Vaporization (liquid to gas) and condensation (gas to liquid) involve latent heat of vaporization
• Sublimation (solid to gas) and deposition (gas to solid) occur in some substances (dry ice)
• Latent heat explains why sweating cools the body (evaporative cooling)