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Edexcel A Level (IAL) Physics-5.1 Specific Heat Capacity & Latent Heat- Study Notes- New Syllabus

Edexcel A Level (IAL) Physics -5.1 Specific Heat Capacity & Latent Heat- Study Notes- New syllabus

Edexcel A Level (IAL) Physics -5.1 Specific Heat Capacity & Latent Heat- Study Notes -Edexcel A level Physics – per latest Syllabus.

Key Concepts:

  • be able to use the equations ΔE = mcΔθ and ΔE = LΔm

Edexcel A level Physics-Study Notes- All Topics

Thermal Energy Transfer: Specific Heat Capacity and Latent Heat

When thermal energy is transferred to or from a substance, the effect depends on whether the substance’s temperature changes or whether a change of state occurs. These processes are described using two key equations.

 Heating or Cooling with Temperature Change

Equation:

\( \Delta E = mc\Delta\theta \)

Meaning of symbols:

  • \( \Delta E \) = thermal energy transferred (J)
  • \( m \) = mass of the substance (kg)
  • \( c \) = specific heat capacity (J kg⁻¹ K⁻¹)
  • \( \Delta\theta \) = change in temperature (K or °C)

Key ideas:

  • This equation applies when there is no change of state.
  • The temperature of the substance increases or decreases.
  • A larger mass or larger temperature change requires more energy.

Specific Heat Capacity

Definition:

The specific heat capacity of a substance is the thermal energy required to raise the temperature of 1 kg of the substance by 1 K.

  • Substances with large \( c \) heat up slowly.
  • Substances with small \( c \) heat up quickly.

Change of State at Constant Temperature

Equation:

\( \Delta E = L\Delta m \)

Meaning of symbols:

  • \( \Delta E \) = thermal energy transferred (J)
  • \( L \) = specific latent heat (J kg⁻¹)
  • \( \Delta m \) = mass undergoing change of state (kg)

Key ideas:

  • The temperature remains constant.
  • Energy is used to break or form intermolecular bonds.
  • No temperature change occurs during melting, boiling, freezing, or condensing.

 Types of Latent Heat

  • Latent heat of fusion: solid ↔ liquid
  • Latent heat of vaporisation: liquid ↔ gas

Choosing the Correct Equation

  • Use \( \Delta E = mc\Delta\theta \) when temperature changes.
  • Use \( \Delta E = L\Delta m \) when a change of state occurs.
  • In some problems, both equations may be needed in sequence.

 Energy Transfer Curves

  • Sloping sections: temperature changes → use \( \Delta E = mc\Delta\theta \)
  • Flat sections: change of state → use \( \Delta E = L\Delta m \)

Example (Easy)

Calculate the energy needed to raise the temperature of \( 2.0\ \mathrm{kg} \) of water by \( 5.0\ \mathrm{K} \). (Take \( c = 4200\ \mathrm{J\,kg^{-1}\,K^{-1}} \))

▶️ Answer / Explanation

\( \Delta E = mc\Delta\theta = 2.0 \times 4200 \times 5.0 = 4.2\times10^{4}\ \mathrm{J} \)

Example (Medium)

How much energy is required to melt \( 0.50\ \mathrm{kg} \) of ice at \( 0^\circ\mathrm{C} \)? (Take \( L = 3.3\times10^{5}\ \mathrm{J\,kg^{-1}} \))

▶️ Answer / Explanation

\( \Delta E = L\Delta m = 3.3\times10^{5} \times 0.50 = 1.65\times10^{5}\ \mathrm{J} \)

Example (Hard)

Explain why energy is still required during boiling even though the temperature remains constant.

▶️ Answer / Explanation
  • Energy is used to overcome intermolecular forces.
  • No increase in kinetic energy occurs.
  • The energy increases potential energy instead.
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