Question

How much heat is given off by 1,000 kg of lead when it solidifies at its melting point?(see the table)

Substance: Heat of Fusion(J/kg)
copper 2.66 x 10^5
iron 2.66 x 10^5
silver 1.04 x 10^5
lead 2.04 x 10^4
gold 6.30 x 10^4

Answers:
(a): 4.90 x 10^-2 J
(b): 2.04 x 10 J
(c) 2.04 x 10^8 J
(d) 2.04 x 10^7 J

(P.S x=multiply its not an exponent btw)

Answer 1

At the melting point the heat given off is the latent heat of fusion. This occurs with at the melting point. It is not associated with temperature change.

All melting and solidification or freezing occur at the melting point temperature.

Q = mL      (This formula is associated with fusion or vaporization process)

Where Q = Heat associated with the melting process
m = mass in kg,
L = Latent heat of fusion in J/kg

For lead so we select the latent heat of fusion for lead.  Mass = 1000 kg

Q = 1000 kg * 2.04 x 10^4 J/kg

Q = 2.04 * 10^7  J

Option D.