kJ are required to melt a 43.5 g sample of solid silicon, Si, at its normal melting point.

Question

The following information is given for silicon at 1 atm:

boiling point = 2355 °C	Hvap(2355 °C) = 297 kJ/mol
melting point = 1410 °C	Hfus(1410 °C) = 46.4 kJ/mol
specific heat solid = 0.711 J/g°C
specific heat liquid = 0.908 J/g°C

Answer 1

The heat needed to melt something is the mass of the material x the heat of fusion.

q = m∆H_fusion

m = mass = 43.5 g

∆H_fusion = 46.4 kJ/mol x 1 mol Si / 28.09 g Si = 1.65 kJ/g Si

q = (43.5 g)(1.65 kJ / g) = 71.9 kJ required to melt the silicon