You have a 5.0 kg lead block at room temperature. Find the energy required to raise the lead's temperature to its melting point. Also Find the energy required to melt the lead once it's reached the melting point. I've already found the answer for the first part for the energy required to raise the temp which is 2.0*10^5 J. However, I've been trying to solve the second part for the energy required to melt after its reached the melting point. I've tried 1.25*10^5J using Q=mLf -- =(5)*(2.5*10^4)= 1.25*10^5 J, however, it's saying that I am wrong. Then I also put 118750 J, and it's wrong too.

Question

You have a 5.0 kg lead block at room temperature. Find the energy required to raise the lead's temperature to its melting point. Also Find the energy required to melt the lead once it's reached the melting point. I've already found the answer for the first part for the energy required to raise the temp which is 2.0*10^5 J. However, I've been trying to solve the second part for the energy required to melt after its reached the melting point. I've tried 1.25*10^5J using Q=mLf --> =(5)*(2.5*10^4)= 1.25*10^5 J, however, it's saying that I am wrong. Then I also put 118750 J, and it's wrong too.

anonymous · Answer

The answer to your problem is given by the equation
Q = mass X latent heat of fusion.
Make sure you use the correct latent heat of fusion.