21 kJ of heat are required to melt 40 g of sodium chloride at its melting point.
The standard enthalpy of fusion of NaCl is 0.52 kJ/g, that is, it takes 0.52 kJ of heat to melt 1 g of NaCl at its melting point. The heat required to melt 40 g of NaCl is:
[tex]40 g \times \frac{0.52kJ}{g} = 21 kJ[/tex]
21 kJ of heat are required to melt 40 g of sodium chloride at its melting point.
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