How much energy a bar of zinc weighing 0.5 kg will acquire when melted at a temperature of 20 degrees.

m = 0.5 kg.

t2 = 420 ° C.

t1 = 20 ° C.

C = 400 J / kg * ° C.

λ = 12 * 10 ^ 4 J / kg.

Q -?

Q = Q1 + Q2, where Q1 is the amount of heat that is needed to heat the bar from t1 to the melting point of zinc t2, Q2 is the amount of heat that is needed to melt the bar itself.

The amount of heat Q1, which is necessary for heating zinc, is determined by the formula: Q = C * m * (t2 – t1), where C is the specific heat capacity of zinc, m is the mass of zinc, t2, t1 are the final and initial temperatures.

The amount of heat Q2, which is necessary for the melting of zinc, is determined by the formula: Q = λ * m, where λ is the specific heat of melting of zinc, m is the mass of zinc.

Q = C * m * (t2 – t1) + λ * m.

Q = 400 J / kg * ° C * 0.5 kg * (420 ° C – 20 ° C) + 12 * 10 ^ 4 J / kg * 0.5 kg = 140,000 J.

Answer: when melted, a zinc bar will acquire Q = 140,000 J of thermal energy.