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  • 1. Objectives At the end of the lesson, students should be able to: define melting and freezing. define boiling and condensation interpret the heating curve
  • 2. Internal energy The internal energy of a body is the combination of the total kinetic energy (due to molecular motion) and potential energy (due to inter- molecular forces) of the molecules in the body. An increase in temperature leads to an increase in the kinetic component of the internal energy. When the temperature increases, the molecule move faster
  • 3. Melting and Freezing Melting is a process in which a substance changes its state from solid to liquid.. Solid Liquid The temperature at which this happens is called the melting point of the substance.
  • 4. Melting and Freezing Freezing is a process in which a substance changes its state from liquid to solid. Solid Liquid The temperature at which this happens is called the freezing point of the substance. Melting point = Freezing point
  • 5. Boiling and Condensation Boiling is the process in which a substance changes from the liquid state to the gaseous state. Liquid Gas The temperature at which this happens is called the boiling point of the substance.
  • 6. Boiling and Condensation Condensation is a process in which a substance changes from the gaseous state to the liquid state. The temperature at which this happens is called the condensation point of the substance. Boiling point = Condensation point
  • 7. State of matter gaseous state boiling point liquid state melting point solid state
  • 8. Change of State solid liquid gas melting / boiling / freezing point condensation point
  • 9. Take note! During the change of state (freezing/melting/boiling/condensation), the temperature of the substance remains constant. For example, when pure ice is melting at 0 °C, it will remain at 0 °C until all the ice has melted. The temperature of pure water will increase beyond 0 °C, when more thermal energy is added to the water.
  • 10. Heating curve Temperature / °C This is a Temperature time graph. In this example, water is being heated from -10 °C As you can see, the temperature of water rises to -10 °C. 0 Time / s -10 ice Heat supplied →
  • 11. Heating curve Temperature / °C When the temperature of water reaches 0 °C, the ice melts. During the change in state, there is no change in temperature even though thermal energy is still being transferred to the water. ice → liquid 0 (melting) Time / s -10 ice Heat supplied →
  • 12. Heating curve Temperature / °C 100 After all the ice has melted, water will liquid continue to increase in Change in state, no temperature change in temperature ice → liquid 0 (melting) Time / s -10 ice Heat supplied →
  • 13. Heating curve Temperature / °C Change in state, no change in temperature liquid → steam 100 (boiling) liquid Change in state, no change in temperature ice → liquid 0 (melting) Time / s -10 ice Heat supplied →
  • 14. Heating curve Temperature / °C 120 Change in state, no change in temperature steam liquid → steam 100 (boiling) liquid Change in state, no change in temperature ice → liquid 0 (melting) Time / s -10 ice Heat supplied →
  • 15. Cooling curve 120 °C steam steam → liquid 100 °C (condensation) liquid 0 °C liquid → ice (freezing) ice -10 °C Heat removed →

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