Given the thermochemical equation: 2NO(g) + O₂(g) → 2NO₂(g) with ΔH° = -1140 kJ, calculate ΔH° for the following reaction: NO₂(g) → NO(g) + 1/2 O₂(g).
A. -570 kJ
B. -1140 kJ
C. 570 kJ
D. 1140 kJ