When C (graphite) reacts with O₂, it gives CO₂. Predict whether ΔH is bigger than ΔU or ΔH is smaller than ΔU and give the reason.
a) ΔH is bigger than ΔU; graphite to CO₂ involves breaking bonds
b) ΔH is smaller than ΔU; graphite to CO₂ involves forming bonds
c) ΔH is equal to ΔU; no bond changes occur
d) ΔH and ΔU are unrelated in this reaction