3.2.5 Heating & Cooling Graphs

• Heating and cooling graphs are essential tools for understanding how substances change temperature over time during heating or cooling processes
• Heating Graph

  • Shows how the temperature of a substance changes as heat is added over time
  • Heating Phase: Temperature rises as heat is added
  • Phase Change Plateaus: Temperature remains constant during phase changes
• Cooling Graph

  • Shows how the temperature of a substance changes as it loses heat over time
  • Cooling Phase: Temperature decreases as heat is removed
  • Phase Change Plateaus: Temperature remains constant during phase changes
• Temperature vs. Time Graph

  • X-Axis: Time (in minutes or seconds)
  • Y-Axis: Temperature (in degrees Celsius or Kelvin)
• Heating Curve Features

  • Initial Slope (Heating Phase): Shows the rate of temperature increase
  • Phase Change Plateaus: Melting Plateau and Boiling Plateau
  • Final Slope (Post-Phase Change Heating): Temperature rises again after phase changes
• Cooling Curve Features

  • Initial Slope (Cooling Phase): Shows the rate of temperature decrease
  • Phase Change Plateaus: Freezing Plateau and Condensation Plateau
  • Final Slope (Post-Phase Change Cooling): Temperature drops further after phase changes
• Identifying Phase Changes

  1. Look for horizontal segments in the graph

  2. Melting/Freezing: Horizontal section at the melting/freezing point

  3. Boiling/Condensation: Horizontal section at the boiling/condensation point
• Calculating Latent Heat

  Use the formula Q = mL during phase changes
• Determining Specific Heat Capacity


  Use the slope of the temperature curve: c = Q/(m Δθ)
• Heating Graph Example

  • Heating ice to water and then boiling it
• Cooling Graph Example

  • Cooling steam to water and then freezing it
• Heating Graph shows how temperature rises and plateaus during phase changes
• Cooling Graph shows how temperature falls and plateaus during phase changes
• Phase Change Plateaus indicate latent heat absorption or release
• Slopes represent the rate of temperature change before and after phase changes
• Latent Heat Calculation is based on the length of phase change plateaus
• Specific Heat Capacity Calculation is based on the slope of temperature changes before and after phase changes
• Understanding these graphs helps explain how energy is used in changing states and managing heat