Answer: The enthalpy change of formation (ΔfH∘) of FeBr3(s) is -269 kJmol−1, which means the amount of energy released when one mole of FeBr3(s) is formed from its constituent elements (Fe and Br) at standard conditions (298K and 1 atm pressure) is -269 kJ.
The enthalpy change of reaction (ΔrH∘) for the reaction 2Fe(s)+3Br2(g) → 2FeBr3(s) is -631 kJ, which means that when the reaction takes place at standard conditions, 631 kJ of energy is released for every mole of FeBr3(s) produced.
We can use the enthalpy of formation and the enthalpy of reaction to calculate the enthalpy of reaction per mole of Fe(s) and per mole of Br2(g).
The balanced equation shows that 2 moles of Fe react with 3 moles of Br2 to produce 2 moles of FeBr3. Therefore, the enthalpy change of reaction per mole of Fe is:
ΔrH∘/2 = -631 kJ/2 = -315.5 kJ/mol
Similarly, the enthalpy change of reaction per mole of Br2 is:
ΔrH∘/3 = -631 kJ/3 = -210.3 kJ/mol
Note that the enthalpy of formation is always for one mole of the substance, so the enthalpy change of formation of FeBr3 can be directly compared to the enthalpy change of reaction per mole of FeBr3.
Overall, the negative values of ΔfH∘ and ΔrH∘ indicate that the formation of FeBr3 from its elements and the reaction of Fe with Br2 to form FeBr3 are exothermic processes, meaning that they release energy to the surroundings.
Step-by-step explanation: