How much heat, in kilojoules, is evolved when a 3.70 kg sample of molten Cu freezes?

The normal boiling point is 1357 K, and heat of fusion is 13.05 KJ/mol.

2.) How much heat must be absorbed at 1357 K to melt a bar of copper (80 * 10 * 12 cm) assume d = 8.93 g/cm^3.

3.78kg Cu x (1000g/1kg) x (1 mol/63.546g) = 59.5

mol Cu
59.5 mol Cu x (13.05kJ/1mol) = 776 kJ evolved

What's the temperature of the molten Cu? I assume it's at the melting point and not above it.

Convert 3.70 kg to moles Cu.
moles Cu x heat fusion = ?? kJ.

2.5*10^4

To find the heat evolved when a sample of molten Cu freezes, we need to use the heat of fusion and the mass of the sample.

1) Heat evolved during freezing:
First, we need to convert the mass of the sample from kg to grams:
3.70 kg = 3700 g

Next, we'll use the molar mass of copper (Cu) to find the number of moles of Cu in the sample. The molar mass of Cu is approximately 63.55 g/mol.

Moles of Cu = Mass (g) / Molar mass of Cu
Moles of Cu = 3700 g / 63.55 g/mol

Now, let's calculate the heat evolved:
Heat evolved = Moles of Cu * Heat of fusion
Heat evolved = (3700 g / 63.55 g/mol) * 13.05 kJ/mol

Therefore, the heat evolved when the 3.70 kg sample of molten Cu freezes is [(3700 g / 63.55 g/mol) * 13.05 kJ/mol] kilojoules.

2) Heat absorbed to melt a bar of copper:
In this case, we need to calculate the volume of the copper bar using its dimensions and density.

Volume = Length * Width * Height
Volume = (80 cm) * (10 cm) * (12 cm) = 9600 cm^3

Next, we convert the volume from cm^3 to m^3:
Volume = 9600 cm^3 * (1 m^3 / 1000000 cm^3) = 0.0096 m^3

Now, let's calculate the mass of the copper bar using the given density:
Mass = Density * Volume
Mass = 8.93 g/cm^3 * 0.0096 m^3

Finally, we need to calculate the heat absorbed:
Heat absorbed = Mass * Heat of fusion

Therefore, the heat that must be absorbed at 1357 K to melt the copper bar is Mass * Heat of fusion kilojoules.