Question

Please help me with the following question. Make sure to explain how you got each step so that I can learn. Please answer the question fully and completely. Thanks in advance!

Answer 1

This is actually easy, the problem state that the melting point of Al is 658 °C which means that passes from solid to liquid, so option B that includes the dH of vaporization can be discarted (vaporization involves liquid to gas). Now, the heat added in that section corresponds to the temperature that goes from 658 to 758 °C, in that section we have the Al in liquid state, so, if we want to calculate the heat added in that section, we actually need the difference in temperature, from the final temperature reached which is 758 °C and the innitial temperature, which is 658 °C.

The second expression that involves dHfus is for the region of fusion, (Where T is constant in 658°C) so this option can be discarted as well.

As I previously state in the section of 658 to 758 we only have the liquid state for aluminum, so we don't need the specific heat of aluminum in solid state, we need the specific heat in the liquid state which we are now, so the expression to get the heat added in that section would be:

Q = m * cp(liq) * (758-658) ----> option D

Hope this helps