Heating and Cooling Curves

Jul 12, 2024

Heating and Cooling Curves

Heating Curve

  • Definition: Shows changes in temperature of a substance during heating.
  • Purpose: Display temperature change over time while heat/energy is added.
  • Initial Phase: Starts at solid phase.
  • Graph Axes:
    • X-axis: Heat absorbed or time.
    • Y-axis: Temperature.
  • Heating Process:
    • Starts with measuring temperature of the cold solid.
    • Heat added gradually, temperature rises.
    • Solid heats until it reaches melting point.
  • Phase Changes:
    • Melting: Solid to liquid
      • Graph: Horizontal/flat.
      • Both solid and liquid present during this stage.
      • Heat absorbed increases potential energy, not kinetic.
    • Liquid Phase: After melting, substance is entirely liquid.
      • Graph: Inclined as temperature increases.
    • Boiling/Evaporation: Liquid to gas
      • Graph: Horizontal/flat.
      • Both liquid and gas present.
    • Gas Phase: After evaporation, substance is entirely gas.
      • Graph: Inclined as temperature increases.

Energy Changes

  • Kinetic Energy:
    • Increases during inclined parts of graph.
    • Higher kinetic energy = higher temperature.
  • Potential Energy:
    • Increases during horizontal/flat parts of graph (phase change).
    • Absorbed heat is used to overcome intermolecular forces.

Cooling Curve

  • Definition: Reverse of the heating curve.
  • Initial Phase: Starts at gas phase.
  • Cooling Process:
    • Gas cools and condenses into liquid.
      • Condensation: Gas to liquid.
      • Graph: Horizontal/flat.
    • Liquid cools further and freezes into solid.
      • Freezing: Liquid to solid.
      • Graph: Horizontal/flat.

Key Points

  • Heating Curve:
    • Add heat continuously.
    • Temperature increases during single-phase intervals (solid, liquid, gas).
    • Temperature constant during phase changes (melting, boiling).
    • Heat absorbed increases kinetic (single-phase) or potential energy (phase change).
  • Cooling Curve:
    • Remove heat continuously.
    • Reverse process of heating.
    • Temperature decreases during single-phase intervals.
    • Temperature constant during phase changes (condensation, freezing).
    • Heat release decreases kinetic (single-phase) or potential energy (phase change).

Visualization

  • Important to know how to interpret, draw and read values from these curves.

Note: Always include graph heading, axis labels, and units on actual graphs for clarity.