Lecture Notes: Specific Latent Heat

Key Concepts

• Specific Latent Heat: The energy required to change the state of 1 kg of a substance without changing its temperature.
  • Two types:
    • Specific Latent Heat of Vaporization: Energy for phase change between liquid and gas.
    • Specific Latent Heat of Fusion: Energy for phase change between solid and liquid.

Understanding Temperature and State Changes

• Kinetic Energy and Temperature: Heating a substance increases particle energy, thus increasing temperature.
• Exception: During state changes (melting, boiling), temperature remains constant as energy is used to break/form bonds.

Graph Analysis

• Heating: Temperature rises until state change (melting/boiling) where it plateaus.
• Cooling: Temperature drops but remains constant during state change due to energy release from bond formation.

Calculations Involving Specific Latent Heat

• Formula:

  [ \text{Energy (J)} = \text{Mass (kg)} \times \text{Specific Latent Heat (J/kg)} ]

• Example Problem:

  • Calculate energy to boil 2.5 kg of water at 100°C.

  • Use specific latent heat of vaporization: (2,260,000 \text{ J/kg}).

  • Calculation:

    [ 2.5 \times 2,260,000 = 5,650,000 \text{ J (or 5,650 kJ)} ]

Practical Application

• Ice to Vapor Example:
  • Heat 1 kg of ice from -50°C to 150°C through state changes.
  • Specific latent heat of fusion for water: 334,000 J/kg.
  • Specific latent heat of vaporization for water: 2,260,000 J/kg.

Conclusion

• During heating or cooling, energy is needed or released without temperature change during state transitions.
• These values (specific latent heat) are provided in exams when needed.

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