2 C2H6 + 7 02 -> 4CO2 + 6H2O
If 15 g of C2H6 react with 45 g of O2, how many grams of water will be produced?

Mass of water = 21.6 g

Explanation:

Given data:

Mass of C₂H₆ = 15 g

Mass of O₂ = 45 g

Mass of water produced = ?

Solution:

Chemical equation:

2C₂H₆ + 7O₂     →       4CO₂ + 6H₂O

Number of moles of C₂H₆:

Number of moles = mass/ molar mass

Number of moles = 15 g/ 30 g/mol

Number of moles = 0.5 mol

Number of moles of O₂ :

Number of moles = mass/ molar mass

Number of moles = 45 g/ 32 g/mol

Number of moles = 1.4 mol

Now we will compare the moles of C₂H₆ and O₂ with H₂O.

                           C₂H₆           :                H₂O

                             2               :                  6

                           0.5              :          6/2×0.5 = 1.5

                            O₂              :                H₂O

                             7               :                  6

                           1.4               :           6/7×1.4 = 1.2

The number of moles of water produced by  oxygen are less so it will limiting reactant.

Mass of water produced:

Mass = number of moles × molar mass

Mass = 1.2 mol × 18 g/mol

Mass = 21.6 g