MCAT Physics Chapter 3: Thermodynamics

Introduction

• Study of energy flow in the universe related to work, heat, entropy, and energy forms.
• Four objectives:
  1. Zeroth Law of Thermodynamics
  2. Systems in Thermodynamics
  3. First Law of Thermodynamics
  4. Second Law of Thermodynamics

Zeroth Law of Thermodynamics

• Principle: If two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other.
• Establishes concept of temperature.
• Example: Thermal equilibrium between a cup of warm tea, metal stirring stick, and hand.
• Key Point: No heat flows between objects in thermal equilibrium.

Temperature Scales

• Celsius: 0°C is freezing point, 100°C is boiling point of water.
• Fahrenheit: 32°F is freezing point, 212°F is boiling point of water.
• Kelvin: Absolute zero as reference point, 273K is freezing point, 373K is boiling point of water.
• Conversions:
  • °C = 5/9 (°F - 32)
  • °F = 9/5 °C + 32
  • K = °C + 273

Practice Problem

• Convert 86°F to Celsius and Kelvin:
  • Celsius: (5/9) * (86 - 32) = 30°C
  • Kelvin: 30 + 273 = 303K*

Thermal Expansion

• Physical properties change with temperature: length, volume, solubility, conductivity.
• Linear Expansion Formula: ΔL = αL₀ΔT
  • α: coefficient of linear expansion.
• Volumetric Expansion Formula: ΔV = βV₀ΔT
  • β: coefficient of volumetric expansion.

Practice Problems

1. Metal rod 2m, cooled from 1080°C to 80°C, α = 10⁻⁶/K:

   • ΔL = 2m * 10⁻⁶/K * (80 - 1080) = -2 * 10⁻³m
   • Final length = 1.998m

2. Mercury thermometer, expands from -25°C to 225°C, β = 1.8 * 10⁻⁴/K:

   • ΔV = 1.8 * 10⁻⁴ * 1ml * (225 - (-25)) = 0.045ml*

Summary

• Zeroth Law: Equilibrium and temperature.

• Temperature Scales: Conversions between Celsius, Fahrenheit, Kelvin.

• Thermal Expansion: Influence on physical properties.

• Next steps: Explore systems and first/second laws of thermodynamics in upcoming sessions.