Final answer:
For the formation of 1.0 mole of HBr from the reaction of H2 and Br2, which has a ΔH° of -72 kJ for 2 moles of HBr, the heat evolved is -36 kJ, as the reaction is exothermic.
Step-by-step explanation:
The question asks how many kJ of heat will be evolved when 1.0 mole of HBr is formed given that the value of ΔH° for the reaction H2(g) + Br2(g) → 2HBr(g) is -72 kJ. Since the enthalpy change (ΔH°) of -72 kJ corresponds to the formation of 2 moles of HBr, to find the heat evolved for the formation of 1 mole of HBr, we simply divide this value by 2.
The calculation is as follows:
ΔH° for 2 moles of HBr = -72 kJ
ΔH° for 1 mole of HBr = -72 kJ / 2 = -36 kJ
Therefore, when 1.0 mole of HBr is formed, 36 kJ of heat will be evolved. Because the reaction is exothermic, this value is negative, indicating that heat is released during the reaction.