The temperature dependence of the heat capacity of a substance is commonly written in the form C_P,m = a + bT+ c/T², with a, b, and c constants. Obtain an expression for the entropy change when the substance is heated from T₁ to T₂. Evaluate this change for graphite, for which a = 16.86 J · K^–1?mol^–1, b = 4.77 mJ · K^–2 · mol^–1, and c = 28.54 * 105 J · K · mol^–1, heated from 298 K to 400. K. What is the percentage error in assuming that the heat capacity is constant with its mean value in this range?