Question

The following thermochemical equation is for the reaction of iron(III) oxide(s) with hydrogen(g) to form iron(s) and water(g). Fe2O3(s) + 3H2(g)— 2Fe(s) + 3H2O(g) AH = 98.8 kJ When 62.3 grams of iron(III) oxide(s) react with excess hydrogen(g), kJ of energy are Hint: An amount of energy is expressed as a positive number. The sign of AH in the thermochemical equation indicates whether the energy is absorbed or evolved.

Answer 1

1)

Molar mass of Fe2O3,

MM = 2*MM(Fe) + 3*MM(O)

= 2*55.85 + 3*16.0

= 159.7 g/mol

mass(Fe2O3)= 62.3 g

use:

number of mol of Fe2O3,

n = mass of Fe2O3/molar mass of Fe2O3

=(62.3 g)/(1.597*10^2 g/mol)

= 0.3901 mol

Since Δ H is positive, heat is absorbed

when 1 mol of Fe2O3 reacts, heat absorbed = 98.8 KJ

So,

for 0.3901 mol of Fe2O3, heat absorbed = 0.3901*98.8/1 KJ

= 38.54 KJ

Answer: 38.5 KJ, ABSORBED

2)

W = -523 J

Delta E = -2658 J

Use:

Delta E = Q + W

-2658 J = Q - 523 J

Q = -2135 J

Answer: -2135 J