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.