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?

Answer 1

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

Divide the number of moles Na by the 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"#

Calculate Na's mass by dividing it by its molar mass, or atomic weight expressed 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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Answer 2

Noah Aldrich

The mass of the NaCl sample needed to melt completely is 24.3 grams.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.