How much heat is needed to melt a piece of lead weighing 2 kg taken at a temperature of 27 degrees Celsius?

Problem data: m (mass of a piece of lead) = 2 kg, t (temperature of lead before heating and melting) = 27 ºС.

Reference data: tmelt (melting onset temperature) = 327 ºС; C (specific heat) = 140 J / (K * kg), λ (specific heat of fusion) = 25 * 10 ^ 3 J / kg.

The amount of heat for heating and melting lead is determined by the formula: Q = C * m * (tpl – t) + λ * m = (C * (tpl – t) + λ) * m.

Calculation: Q = (140 * (327 – 27) + 25 * 10 ^ 3) * 2 = 134000 J (134 kJ).

Answer: You need 134 kJ of heat.