Question #ce902

1 Answer
Ernest Z.
Dec 29, 2016

You can't get the answer because your value of #ΔH# is incorrect.

Explanation:

The correct value of #ΔH# is -851.5 kJ.

Start with the balanced equation.

#"2Al(s)" + "Fe"_2"O"_3"(s)" → "2Fe(s)" + "Al"_2"O"_3"(s)"; ΔH = "–851.5 kJ"#

Step 1. Calculate the moles of #"Al"# used

#"Moles of Al" = 36 color(red)(cancel(color(black)("g Al"))) × "1 mol Al"/(26.98 color(red)(cancel(color(black)("g Al")))) = "1.33 mol Al"#

Step 2. Calculate the heat evolved

#"Heat evolved" = 1.33 color(red)(cancel(color(black)("mol Al"))) × "- 851.5 kJ"/(2 color(red)(cancel(color(black)("mol Al")))) = "-570 kJ"# (2 significant figures)

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