Given that the molar heat of fusion of sodium (Na <--solid) is +2.63KJ/mol, how much potential energy is needed to completely melt 180g of solid sodium at its melting point?
a) 2.63KJ
b) 2.98KJ
c) 20.6KJ
d) 473KJ
a) 2.63KJ
b) 2.98KJ
c) 20.6KJ
d) 473KJ
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First you need to know how many moles of sodium you have. The atomic weight (molar mass) of sodium is 23 (rounding a little bit). So 180 grams / 23 grams per mole = 7.83 moles. The heat of fusion is 2.63 KJ/mol, so 7.83 multiplied by 2.63 = 20.58 which rounds to 20.6 which is "c"
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(2.63kJ/mol) (180 g / 23 g/mol) = 20.5826 kJ
Three sig figs is reasonable: 20.6 kJ
Three sig figs is reasonable: 20.6 kJ