Why does the specific heat capacity of a solid generally agree with 3R at ordinary temperatures?
**Isobaric process** constant pressure, work W = P ΔV = P(V₂ - V₁) = n R ΔT, for expansion ΔV positive W positive, for compression negative, heat Q = n C_p ΔT, ΔU = n C_v ΔT. Isothermal process constant temperature ΔU=0, work W = n R T ln(V₂/V₁) = n R T ln(P₁/P₂), Q = W, heat absorbed equals work done. The law of equipartition predicts that each atom in a solid has 3 degrees of freedom (vibrational), contributing (3)/(2) k_B T kinetic and potential energy per atom. For a mole, U = 3 R T , so C = (Δ U)/(Δ T) =
Ref: NCERT > Physics Book > Thermodynamics > Isobaric and Isothermal Processes Work Calculation