Question

Use the following thermochemical equation.

Fe₂O₃(s) + 3CO(g) → 2Fe(s) + 3CO₂(g) ΔH° = −26.8 kJ

What is the value of ΔH when 235 g of iron(III) oxide reacts completely?
a. −35.7 kJ
b. −38.4 kJ
c. −39.4 kJ
d. −36.7 kJ

Answer 1

The correct answer is option a. −35.7 kJ.

Step-by-step explanation:

To calculate the heat released (ΔH) when 235 grams of iron(III) oxide (Fe2O3) reacts, we can use the provided thermochemical equation and the given change in enthalpy (ΔH° = −26.8 kJ) for the reaction as it is written. Since the equation shows the enthalpy change for moles of substances, we need to first convert the mass of Fe2O3 to moles.

The molar mass of Fe2O3 is (55.85 g/mol × 2) + (16.00 g/mol × 3) = 159.7 g/mol. Therefore, the number of moles of Fe2O3 is:

235 g Fe2O3 × (1 mol Fe2O3 / 159.7 g Fe2O3) = 1.472 moles Fe2O3

We then scale the ΔH° value according to the moles:

1.472 moles Fe2O3 × (−26.8 kJ / 1 mol Fe2O3) = −35.7 kJ

The value of ΔH when 235 g of Fe2O3 reacts completely is −35.7 kJ.