Consider the combination reaction: 2Mg(s) + O2(g) → 2MgO(s) with ΔH = -1204 kJ. What is the enthalpy change for the decomposition of 1 mole of MgO(s) into Mg(s) and O2(g)?

• A. -602 kJ
• B. -1204 kJ
• C. +1204 kJ
• D. +602 kJ

Answer: (D)

Verified step by step guidance

1. Understand that the given reaction is a combination reaction where magnesium (Mg) reacts with oxygen (O2) to form magnesium oxide (MgO) with an enthalpy change (ΔH) of -1204 kJ for the formation of 2 moles of MgO.
2. Recognize that the decomposition of MgO is the reverse of the given reaction. In a reverse reaction, the sign of the enthalpy change is also reversed.
3. Since the given reaction forms 2 moles of MgO with ΔH = -1204 kJ, the reverse reaction (decomposition) for 2 moles of MgO will have an enthalpy change of +1204 kJ.
4. To find the enthalpy change for the decomposition of 1 mole of MgO, divide the enthalpy change for 2 moles by 2.
5. Calculate the enthalpy change for 1 mole of MgO: ΔH = +1204 kJ / 2 = +602 kJ. This is the enthalpy change for the decomposition of 1 mole of MgO into Mg and O2.