Lecture on Specific Latent Heat

Objectives

• Understand the concept of specific latent heat.
• Learn to calculate the energy change during a state change of a substance.

Key Concepts

Understanding Specific Latent Heat

• Specific Latent Heat: Energy required to change the state of 1 kg of a substance with no temperature change.
• This energy is used to weaken or break the forces of attraction between particles during a state change.

Types of Latent Heat

• Specific Latent Heat of Fusion:
  • Energy required to change 1 kg of a substance from solid to liquid at constant temperature.
  • Example: Melting 1 kg of ice requires 334,000 Joules.
• Specific Latent Heat of Vaporization:
  • Energy required to change 1 kg of a substance from liquid to vapor at constant temperature.

Calculating Energy Change

• Formula:

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

• This formula will be provided in exams along with specific latent heat values.

Example Calculations

1. Melting Ice

   • Convert 0.5 kg of ice to liquid water.
   • Specific latent heat of fusion: 334,000 J/kg.
   • Calculation: [ 0.5 \text{ kg} \times 334,000 \text{ J/kg} = 167,000 \text{ J} ]

2. Vaporizing Ethanol

   • Convert 0.15 kg of ethanol from liquid to vapor.
   • Specific latent heat of vaporization: 846,000 J/kg.
   • Calculation: [ 0.15 \text{ kg} \times 846,000 \text{ J/kg} = 126,900 \text{ J} ]

Additional Resources

• Practice questions on specific latent heat are available in the revision workbook.

Conclusion

• Able to describe specific latent heat and calculate energy changes during state changes.