Answer:
[tex]{\rm 1\; C_3H_8} + {\rm 5\; O_2} \to {3\; \rm CO_2} + {4\; \rm H_2O}[/tex].
Explanation:
[tex]{\rm ?\; C_3H_8} + {\rm ?\; O_2} \to {?\; \rm CO_2} + {?\; \rm H_2O}[/tex].
Among the four species in this reaction, [tex]\rm C_3H_8[/tex] is species with the largest number of atoms per molecule. Assume that the coefficient of this compound is [tex]1[/tex].
[tex]{\rm 1\; C_3H_8} + {\rm ?\; O_2} \to {?\; \rm CO_2} + {?\; \rm H_2O}[/tex].
Number of atoms on the left-hand side of the reaction:
By the conservation of atoms, the number of atoms on the right-hand side of the reaction should match those on the left-hand side. In this reaction, [tex]\rm CO_2[/tex] is the only product with carbon atoms, whereas [tex]\rm H_2O[/tex] is the only product with hydrogen atoms. These [tex]3[/tex] carbon atoms and [tex]8[/tex] hydrogen atoms would correspond to:
[tex]{\rm 1\; C_3H_8} + {\rm ?\; O_2} \to {3\; \rm CO_2} + {4\; \rm H_2O}[/tex].
Number of atoms on the right-hand side of the reaction:
The number of [tex]\rm O[/tex] atoms on the left-hand side should match those on the right-hand side. In this reaction, [tex]\rm O_2[/tex] is the only reactant with [tex]\rm O\![/tex] atoms. These [tex]10[/tex] [tex]\rm \! O[/tex] atoms would correspond to:
[tex]{\rm 1\; C_3H_8} + {\rm 5\; O_2} \to {3\; \rm CO_2} + {4\; \rm H_2O}[/tex].
