# Question ce902

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.

$\text{2Al(s)" + "Fe"_2"O"_3"(s)" → "2Fe(s)" + "Al"_2"O"_3"(s)"; ΔH = "–851.5 kJ}$
Step 1. Calculate the moles of $\text{Al}$ used
$\text{Moles of Al" = 36 color(red)(cancel(color(black)("g Al"))) × "1 mol Al"/(26.98 color(red)(cancel(color(black)("g Al")))) = "1.33 mol Al}$
$\text{Heat evolved" = 1.33 color(red)(cancel(color(black)("mol Al"))) × "- 851.5 kJ"/(2 color(red)(cancel(color(black)("mol Al")))) = "-570 kJ}$ (2 significant figures)