Phase change: For silicon , Si , the heat of fusion at its normal melting point

Question

Phase change:

For silicon, Si, the heat of fusion at its normal melting point of 1410 °C is 46.4 kJ/mol.

The entropy change when 2.08 moles of liquid Si freezes at 1410 °C, 1 atm is  J/K.

For n-pentane, C5H12, the heat of vaporization at its normal boiling point of 36 °C is 25.8 kJ/mol.

The entropy change when 2.35 moles of C5H12 vapor condenses at 36 °C, 1 atm is  J/K.

For magnesium, Mg, the heat of fusion at its normal melting point of 649 °C is 9.0 kJ/mol.

The entropy change when 1.96 moles of solid Mg melts at 649 °C, 1 atm is  J/K.

Explanation / Answer

Entropy change = -(heat of fusion)/temperature

For Si:

Entropy change = -(46.4 kJ/mol*2.08 mol)/(1410+273.5)K = -0.0573 kJ/K = -57.3 J/K

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