Let a, b, c, d be coefficients that balance the reaction,
a C₆H₁₄ + b O₂ ⇒ c CO₂ + d H₂O
Count the number of each atom on either side, and solve for a, b, c, d.
• C : 6a = c
• H : 14a = 2d
• O : 2b = 2c + d
Suppose a = 1. Then
6a = c ⇒ c = 6
14a = 2d ⇒ 2d = 14 ⇒ d = 7
2b = 2c + d ⇒ 2b = 19 ⇒ b = 19/2
So, the balanced reaction is
C₆H₁₄ + 19/2 O₂ ⇒ 6 CO₂ + 7 H₂O
which says 1 mol C₆H₁₄ can react with 9.5 mol O₂.
Convert the given mass of C₆H₁₄ to moles. (C₆H₁₄ has a molar mass of about 86.18 g/mol.)
(10.4 g) (1/86.18 mol/g) ≈ 0.121 mol C₆H₁₄
Multiply this amount by 9.5 to find the requisite amount of O₂ needed:
9.5 (0.1207 mol) ≈ 1.15 mol O₂
Finally, convert this amount of O₂ to a mass. (O₂ has a molar mass of about 31.998 g/mol.)
(1.15 mol) (31.998 g/mol) ≈ 36.7 g O₂
