FOCUS ON: Understanding and Calculating Specific Latent Heat

Part 1 - Keywords:

1. Specific Latent Heat

2. Thermal Energy

3. Latent Heat of Fusion

4. Latent Heat of Vaporisation

5. Phase Change

6. Calculations

7. Measuring

8. Practical

9. Example Calculation

Part 2 - Key Facts:

Definition of Specific Latent Heat:

• Specific Latent Heat is the amount of energy needed to change the state of 1 kilogram of a substance without changing its temperature.

Explanation:

• When a substance undergoes a phase change, such as melting or boiling, energy is absorbed or released without a change in temperature. This energy is specific latent heat.

Latent Heat of Fusion and Vaporisation:

• Latent Heat of Fusion: The energy needed to change 1 kg of a substance from a solid to a liquid at its melting point.

• Latent Heat of Vaporisation: The energy needed to change 1 kg of a substance from a liquid to a gas at its boiling point.

Calculating Thermal Energy Changes:

• The formula for calculating thermal energy changes , in joules, J (E) is E = m × L, where m is the mass in kilograms, kg of the substance and L is the specific latent heat in joules per kilogram, J/kg.

Measuring Latent Heat - Practical:

1. Heat a substance until it reaches its melting or boiling point.

2. Continue heating, and measure the energy input needed to change the state.

3. Use the formula E = m × L to calculate specific latent heat.

Example Calculation:

• Calculate the energy needed to melt 0.5 kg of ice (latent heat of fusion of ice is 334,000 J/kg).

Answer:

• E = m × L

• = 0.5 kg × 334,000 J/kg

• = 167,000 J

Part 3 - Quick Quiz:

1. What does specific latent heat measure?

   a) Temperature change

   b) Phase change energy

   c) Thermal conductivity

   Answer: b) Phase change energy

2. Which formula is used to calculate thermal energy changes involving specific latent heat?

   a) E = mcΔT

   b) E = mL

   c) P = IV

   Answer: b) Q = mL

3. What is the latent heat of vaporisation?

   a) Energy needed to freeze a substance

   b) Energy needed to change a substance from a liquid to a gas

   c) Energy needed to change a substance from a solid to a liquid

   Answer: b) Energy needed to change a substance from a liquid to a gas

Part 4 - Going Further:

Question: Explain the significance of specific latent heat in thermal energy changes. How does it contribute to the understanding of phase changes?

Answer: Specific latent heat is crucial in understanding phase changes as it quantifies the amount of energy required for substances to transition between states without a temperature change. The concept is essential for various applications, such as designing cooling systems and understanding energy transfer during phase transitions.

Part 5 - Revision Tips: Focus on grasping the definition of specific latent heat, understanding the formulas for calculating thermal energy changes, and practicing practical scenarios involving phase changes.

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Stay tuned for the next issue, where we'll explore more captivating topics in GCSE Physics.