The reaction of iron with hydrochloric acid is represented by the following thermochemical equation.
Fe(s) + 2HCl(aq) → FeCl₂(aq) + H₂(g) ; ΔH° = -87.9 kJ
How much heat is liberated at constant pressure if 0.154 g of iron reacts with 25.7 mL of 0.358 M HCl?

Question

Quizplus · Accepted Answer

First, determine the moles of iron (Fe) that reacted. The molar mass of Fe is approximately 55.85 g/mol. So, $0.154 \, \text{g Fe} \times \frac{1 \, \text{mol Fe}}{55.85 \, \text{g Fe}} = 0.00276 \, \text{mol Fe}$. Then, since the reaction is 1:1 for Fe to HCl, and given that there is excess HCl, the amount of heat liberated is directly proportional to the amount of Fe. Using the given $\Delta H^\circ = -87.9 \, \text{kJ}$ for the reaction of 1 mole of Fe, the heat for $0.00276 \, \text{mol Fe}$ is $0.00276 \, \text{mol Fe} \times -87.9 \, \text{kJ/mol} = -0.242 \, \text{kJ}$, indicating that 0.242 kJ of heat is liberated.

The Reaction of Iron with Hydrochloric Acid Is Represented by the Following