Final answer:
When 4.90 grams of Fe₂O₃ reacts with excess carbon monoxide, a total of -0.761 kJ of heat is evolved.
Step-by-step explanation:
To calculate the amount of heat evolved when 4.90 g of Fe₂O₃ is reacted with excess carbon monoxide according to the given equation, we first need to determine the moles of Fe₂O₃ that are present. The molecular weight of Fe₂O₃ is approximately 159.7 g/mol. So the moles of Fe₂O₃ in 4.90 g are calculated as 4.90 g / 159.7 g/mol = 0.0307 mol.
Next, using the stoichiometry of the equation Fe₂O₃(s) + 3 CO(g) → 2 Fe(s) + 3 CO₂(g), we see that 1 mole of Fe₂O₃ results in an enthalpy change (ΔH°rxn) of -24.8 kJ. Therefore, 0.0307 mol will release 0.0307 mol × -24.8 kJ/mol = -0.7614 kJ of heat.
Since we typically report enthalpy changes in kilojoules, the final answer is rounded to three significant figures: -0.761 kJ of heat evolved.