A sample of 6.50 g of liquid 1‑propanol, C3H8O, is combusted with 37.1 g of oxygen gas. Carbon dioxide and water are the products.

Question

A sample of 6.50 g of liquid 1‑propanol, C3H8O, is combusted with 37.1 g of oxygen gas. Carbon dioxide and water are the products.

Write the balanced chemical equation for the reaction. Physical states are optional.

chemical reaction:

How many grams of the excess reactant remain after the reaction is complete?

mass of excess reactant remaining: ?g

Answer 1

2 C₃H₈O + 9 O₂ → 6 CO₂ + 8 H₂O

The stoichiometric molar ratio of O₂ to C₃H₈O is 4.5 : 1. If the reaction's molar ratio is

1. less than 4.5 : 1 then there is excess C₃H₈O and O₂ is the limiting reagent
2. greater than 4.5 : 1 then there is excess O₂ and C₃H₈O is the limiting reagent

37.1 g O₂ × (1 mol)/(32 g) = 1.159 mol O₂

6.5 g C₃H₈O × (1 mol)/60.1 g) = 0.108 mol C₃H₈O

The O₂ to C₃H₈O molar ratio in the reaction is 1.159 : 0.108 = 10.7 : 1

Since this is greater than the 4.5 : 1 there is excess O₂ and C₃H₈O is the limiting reagent.

0.108 mol C₃H₈O will react with 4.5 × 0.108 = 0.486 mol O₂

1.159 – 0.486 = 0.673 mol excess O₂ remain unreacted.

0.673 mol O₂ × 32 g/mol = 21.5 g unreacted O₂

Answer

mass of excess reactant O₂ remaining: 21.5 g