Chemistry Homework Help! Combustion!

Question

1. How many moles of water is produced by the complete combustion of 5 g of propane
2. Convert this answer into grams
3. Show that the conservation of mass was a balanced during the complete combustion of propane by calculating and showing the sum of the masses (in grams) of the reactants are equal to the sum of the masses of the products (in grams).

Answer 1

First, you need to write the overall reaction!

Propane: C₃H₈

C₃H₈ + 5O₂ -> 3CO₂ + 4H₂O

Second, convert 5 g of propane to moles!

The molar mass of propane: 44 g/mol

5 grams* 1/(44 g/mol) * (4 mol H₂O)/(1 mol C₃H₈) = 5/11 mols of H₂O

Third, multiply it with the molar mass of H₂O: 18 g/mol

5/11 mols of H₂O * 18 g/mol = 90/11 g of H₂O

Lastly, to show conservation of mass as stated by the problem, you need to find how much oxygen is consumed, as well as how much CO₂ is made.

5 grams* 1/(44 g/mol) * (5 mol O₂)/(1 mol C₃H₈) = 25/44 mol O₂

Molar mass of O₂: 32 g/mol

25/44 of mol O₂ * 32 g/mol = 200/11 g of O₂

5 grams* 1/(44 g/mol) * (3 mol CO₂)/(1 mol C₃H₈) = 15/44 mol of CO₂

Molar mass of CO₂: 44 g/mol

15/44 mol of CO₂ * 44 g/mol = 15 g of CO₂

Reactants: 5 g of C₃H₈ + 200/11 g of O₂ = 255/11 g

Products: 90/11 g of H₂O + 15 g of CO₂ = 255/11 g

Thus, showing the conservation of mass!