Hydrogen iodide (HI) is formed from the reaction of the elements hydrogen and iodine H2(g) + I2(g) → 2HI(g); ΔH = +52 kJ mol⁻¹ When two moles of HI decompose A - VCE - SSCE Chemistry - Question 3 - 2006 - Paper 1

The given reaction for the formation of hydrogen iodide (HI) indicates that it has an enthalpy change ( ΔH) of +52 kJ mol⁻¹. This means that when one mole of HI is formed, 52 kJ of energy is absorbed from the surroundings.

When two moles of HI decompose, the energy change is calculated as follows:

$$ext{Energy absorbed or released} = 2 imes ext{ΔH} = 2 imes 52 ext{ kJ} = 104 ext{ kJ}$$

Since the reaction shows a positive ΔH, it indicates that energy is absorbed when the molecules decompose. Therefore, the correct answer is:

D. 104 kJ of energy is absorbed.