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Question

# The normal melting point of copper is $1357 \mathrm{~K}$, and $\Delta_{\text {fus }} \mathrm{H}$ of $\mathrm{Cu}$ is $13.05 \mathrm{~kJ} \mathrm{~mol}^{-1}$. (a) How much heat, in kilojoules, is evolved when a $3.78 \mathrm{~kg}$ sample of molten Cu freezes?

Solution

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Given: Sample of molten Cu = 3.78 kg $\Delta$$\mathrm{H_{fus}}$ of Cu = 13.05 kJ/mol

(1) Calculate for the heat evolved when a 3.78 kg sample of molten Cu freezes in kilojoules as shown below:

Note: Molar mass of Cu = 63.55 g/mol

$\text{Heat evolved,} \Delta\text{H} = \text{(3.78 kg Cu)} (\dfrac{\text{1000 g}}{\text{1 kg}}) (\dfrac{\text{1 mol Cu}}{\text{63.55 g Cu}}) (\dfrac{\text{13.05 kJ}}{\text{1 mol Cu}})$

$\text{Heat evolved,} \Delta\text{H} = \text{776 kJ}$

$\text{Heat evolved,} \Delta\text{H} = \text{-776 kJ}$

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