Mass-mass Stoich

In these type of problems we are starting and ending with both reactants and products in grams.

How many grams of methane are needed to make from 24 grams of water?

We will continue to build off of our previous steps.

Steps to mass-mass problems:

1. Identify what information we are given and what we need to find.

given: 24 g of H₂O , find: grams of CH₄

2. Convert given into moles by dividing by molar mass.

24 g H₂O ÷ 18g/mol H₂O = 1.33 mol H₂O

3. Create a conversion factor from the balanced equation.

We need 1 mole CH₄ for each 2 water.

CH₄ /2H₂O

4. Multiply the given by the conversion factor.

1.33 mol H₂O x CH₄ /2H₂O = ⅔ mol CH₄ *

*Notice that the water needs to be in the denominator to cancel out the water in the numerator.

5. Convert moles to mass by multiplying by the molar mass.

⅔ mol CH₄ x 16.00 g/mol = 10.667g CH₄