More practice questions

4. Q4. Use the 3R rule to estimate the specific heat of silver (molar mass 107.9 g mol^⁻¹), and compare it with NCERT Table 11.1’s 236.1 J kg^⁻¹ K^⁻¹.

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   s = 3R/M = 24.93/0.1079, about 231 J kg^⁻¹ K^⁻¹, within about 2% of the measured 236.1 J kg^⁻¹ K^⁻¹.

5. Q5. How much heat raises the temperature of 3 mol of nitrogen by 20 K at constant pressure? Use C_p = 29.1 J mol^⁻¹ K^⁻¹.

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   Q = μC_pΔT = 3 × 29.1 × 20 = 1746 J, about 1.75 kJ.

6. Q6. Why are the molar specific heats of most solids nearly the same, while their specific heats per kilogram differ a lot?

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   Per mole of atoms, every elemental solid has the same number of atoms, and each vibrating atom stores about 3k_BT, giving about 3R per mole. Per kilogram, the number of atoms depends on the atomic mass, so light elements such as aluminium have a much larger specific heat per kilogram than heavy ones such as lead.