7.
黑火药是中国古代的四大发明之一,其爆炸的热化学方程式为:
\(\rm{S(s)+2KNO_{3}(s)+3C(s)═K_{2}S(s)+N_{2}(g)+3CO_{2}(g) ΔH= x kJ·mol^{-1}}\)
已知碳的燃烧热\(\rm{ΔH_{1}= a kJ·mol^{-1}}\)
\(\rm{S(s)+2K(s)═K_{2}S(s)}\) \(\rm{ΔH_{2}= bkJ·mol^{-1}}\)
\(\rm{2K(s)+N_{2}(g)+3O_{2}(g)═2KNO_{3}(s)}\) \(\rm{ΔH_{3}= ckJ·mol^{-1}}\)
则\(\rm{x}\)为\(\rm{(}\) \(\rm{)}\)