Specific Latent Heat Equation Quiz

Specific Latent Heat Equation

• Energy ( E ) required to change the state of a mass ( m ) is calculated with the formula ( E = mL ).
• Units: ( E ) is in joules (J), ( m ) in kilograms (kg), and ( L ) is the specific latent heat in joules per kilogram (J/kg).
• Rearrangement of the equation can be visualized using a formula triangle.

Values of Latent Heat for Water

• Specific latent heat of fusion for water: 330 kJ/kg.
• Specific latent heat of vaporisation for water: 2.26 MJ/kg.
• Evaporating 1 kg of water utilizes approximately seven times more energy than melting 1 kg of ice to water.

Worked Example

• Energy required when 0.60 kg of stearic acid solidifies, using a specific latent heat of fusion ( L = 199,000 ) J/kg.
• Calculation: ( E = 0.60 , \text{kg} \times 199,000 , \text{J/kg} = 119,400 , \text{J} ).

Definition of Latent Heat

• Latent heat signifies the energy needed to change the state of a mass without changing its temperature.
• Two categories:
  • Specific latent heat of fusion: energy needed to change between solid and liquid states.
  • Specific latent heat of vaporisation: energy needed to change between liquid and gaseous states.

Specific Latent Heat of Fusion

• Defined as the energy to convert 1 kg of a substance from solid to liquid, or vice versa, at a constant temperature.
• Temperature remains constant during melting or freezing until the entire mass transitions.

Specific Latent Heat of Vaporisation

• Defined as the energy to convert 1 kg of a substance from liquid to gas, or vice versa, at a constant temperature.
• Liquid vaporisation maintains constant temperature until all substance is vaporized.

Additional Insights

• The energy transfers during phase changes occur at constant temperatures, leading to periods where temperature does not rise despite continued heating.
• This "hidden" energy referred to as latent heat facilitates breaking intermolecular forces during state changes.
• The concept of latent heat is essential for understanding energy transfers in physical changes of matter.

Exam Tips

• Remember to include the phrase "with no change in temperature" in the definition of specific latent heat for full credit.
• Specific latent heat values are provided during exams; memorization is not necessary.
• Use mnemonic devices to differentiate between fusion (solid to liquid) and vaporisation (liquid to gas) processes.

Test your understanding of the specific latent heat equation and its application to thermal energy changes. This quiz covers the formula E = mL, including key concepts like mass, energy, and latent heat values for water. Evaluate your grasp of these essential ideas in thermodynamics.