Question

How much heat is needed to melt 16.5kg of silver that is initially at 20*C?

Answer 1

22. The silver must be heated to the melting temperature, 961°C, and then melted. We find the heat required
from
Q = msilvercsilver ΔTsilver + msilverLsilver
= (16.50 kg)(230 J/kg · C°)(961°C – 20° C) + (16.50 kg)(0.88 × 105 J/kg) = 5.02 × 106 J.

Answer 2

....................................................................................^^^^^^^^^^^^^^^^^^^^ <----- ???
i get why it's 16.5*230*961-20 but where'd the second part come from

Answer 3

@Kainui help please?

Answer 4

Let's consider water since that's something we can easily relate to. You can have liquid water at 0 degrees C and ice at 0 degrees C.

See, just because you have ice at 0 degrees, you still need to add additional energy into it to make it change its phase from solid to liquid which takes more energy -- but doesn't change the temperature.

Answer 5

As Kainui said, the second part comes from the heat required to change the phase from solid to liquid.

eg. if you wanted to heat ice at -20C to steam, you first have to heat the ice from -20C to 0C.

At that point, any extra heat supplied goes to turning the ice into liquid water. Then, you have to heat the liquid water to 100C, and once it reaches 100C, you have to supply more heat to actually turn the liquid water into steam.

So in that case, there's two phase changes (solid ==> liquid, and liquid ==> gas), as well as the heat required to get ice from -20C to 0C, and the heat required to get water from 0C to 100C.