The heat of fusion of cadmium at its normal melting point of 321 °C is 6.1 kJ/mo
ID: 103570 • Letter: T
Question
The heat of fusion of cadmium at its normal melting point of 321°C is 6.1 kJ/mol, while its heat of vaporization at its normal boiling point of 765°C is 100.0 kJ/mol.
(a) Use these data to calculate the heat of sublimation for Cd _____kJ/mol
Is your answer precise or is it approximate? _________
(b) At 298 K, the standard heat of formation of Cd(s) is 0 kJ/mol while the standard heat of formation of Cd(g) is 111.8 kJ/mol. Use this to calculate the heat of sublimation of cadmium. _____ kJ/mol.
Is your result for part (b) larger or smaller than the value calculated in part (a)? _________
Explanation / Answer
a.
i.
dHsublimtion = dHfusion + dHvapor = 6.1 + 100 = 106.1 kJ/mol
ii
this is approximate, since we are comparing 2 different temperatures, which implies we are assuming the slope is constant. We should use same temperatures for 100% precise data
b.
i
Hsub = Cd(g) - Cd(s) = 111.8-0 = 111.8 kJ/mol
ii
this is larger, since it considers the change in temperature, whereas a won't
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