5.
已知:\(\rm{①CH_{3}OH(g)+\dfrac{3}{2}O_{2}(g) =CO_{2}(g)+2H_{2}O(g)}\) \(\rm{\triangle H=-a kJ·mol^{-1}}\)
\(\rm{②CH_{4}(g)+2O_{2}(g) =CO_{2}(g)+2H_{2}O(g)}\) \(\rm{\triangle H=-b kJ·mol^{-1}}\)
\(\rm{③CH_{4}(g)+2O_{2}(g) =CO_{2}(g)+2H_{2}O(l)}\) \(\rm{\triangle H=-c kJ·mol^{-1}}\)
则下列叙述正确的是\(\rm{(}\) \(\rm{)}\)