How much heat needs to be spent to completely melt a lead strip with a mass of 5 kg taken at a temperature

| September 10, 2021 | education

How much heat needs to be spent to completely melt a lead strip with a mass of 5 kg taken at a temperature of 20 degrees. Is it possible to completely melt such a strip by giving it 500 kJ of energy?

m = 5 kg.

t1 = 20 ° C.

t2 = 327.5 ° C.

C = 140 J / kg * ° C.

q = 25 * 10 ^ 3 J / kg.

Q “= 500 kJ = 500 * 10 ^ 3 J.

Q -?

The required amount of heat Q will be the sum of: Q1 – the amount of heat that is needed to heat lead from t1 to the melting point t2, and Q2 – the amount of heat that is needed to transfer a substance from a solid state to a liquid at the melting temperature.

Q = Q1 + Q2.

Q1 = C * m * (t2 – t1).

Q1 = 140 J / kg * ° C * 5 kg * (327.5 ° C – 20 ° C) = 215250 J.

Q2 = q * m.

Q2 = 25 * 10 ^ 3 J / kg * 5 kg = 125000 J.

Q = 215250 J + 125000 J = 340250 J.

Since Q <Q “, the amount of heat is enough to melt the lead plate.

Answer: to melt a lead strip, you need Q = 340250 J of thermal energy.



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