NaCl has a #DeltaH_(fus)# = 30.2 kJ/mol. What is the mass of a sample of NaCl that needs 732.6 kJ of heat to melt completely?

1 Answer
Meave60
Jun 15, 2017

#"559 g Na"# would need #"732.6 kJ"# of heat to melt completely.

Explanation:

Determine moles Na by dividing by its heat of fusion.

#732.6color(red)cancel(color(black)("kJ"))xx(1"mol Na")/(30.2color(red)cancel(color(black)("kJ")))="24.3 mol Na"#

Determine mass of Na by dividing by its molar mass (atomic weight in g/mol).

#24.3color(red)cancel(color(black)("mol Na"))xx(22.98977"g Na")/(1color(red)cancel(color(black)("mol Na")))="559 Na"# rounded to three sig figs

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