Lesson 3 of 15

Heat Capacity

Heat Capacity

Heat capacity describes how much heat energy a substance must absorb or release to change its temperature by a given amount. It is central to understanding how materials store and transfer thermal energy.

Specific Heat Capacity

The heat required to change the temperature of a mass mm by ΔT\Delta T is:

Q=mcΔTQ = mc\Delta T

Where:

  • QQ is the heat energy added (J)
  • mm is the mass (kg)
  • cc is the specific heat capacity of the material (J/kg·K)
  • ΔT\Delta T is the temperature change (K or °C — they are equivalent for differences)

Common Specific Heats

Materialcc (J/kg·K)
Water4186
Aluminium900
Iron450
Copper385

Water's unusually high specific heat is why it is so effective as a coolant and why coastal climates are mild.

Molar Heat Capacity

For gases and chemical processes it is often more natural to work in moles. The molar heat capacity CvC_v (at constant volume) gives:

Q=nCvΔTQ = nC_v\Delta T

Where nn is the number of moles and CvC_v has units of J/(mol·K).

Mayer's Relation for Ideal Gases

For an ideal gas, the molar heat capacity at constant pressure CpC_p exceeds CvC_v by exactly RR, the universal gas constant:

Cp=Cv+RC_p = C_v + R

Where R=8.314J/(mol\cdotpK)R = 8.314\,\text{J/(mol·K)}. This extra energy accounts for the work the gas does when it expands at constant pressure.

For a monatomic ideal gas: Cv=32R12.47J/(mol\cdotpK)C_v = \frac{3}{2}R \approx 12.47\,\text{J/(mol·K)} and Cp=52R20.79J/(mol\cdotpK)C_p = \frac{5}{2}R \approx 20.79\,\text{J/(mol·K)}.

Your Task

Implement the three functions below. Use R=8.314J/(mol\cdotpK)R = 8.314\,\text{J/(mol·K)} as a module-level constant.

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