Calculations based on chemical equations - mass-mass calculation

Given the balanced chemical equation AND the mass of any one of the reactants or products, the mass of any other reactant or product can be determined by using the appropriate stoichiometric mole ratio of the reactants and products.

Example

How many grams of oxygen gas is required to burn 20.5 grams of ethyl alcohol, C₂H₅OH?

Step 1: Identify the chemical equation involved: a combustion reaction.

Step 2: Write the balanced chemical equation.

Step 2a: Convert the mass of C₂H₅OH to moles of C₂H₅OH.

Step 3: Determine the stoichiometric ratio of the substances that you are working with, specifically between ethyl alcohol and oxygen.

Step 4: Calculate the number of moles of oxygen by making the ratio specifically for the number of moles of C₂H₅OH.

Step 5: Convert the number of moles of oxygen obtained in step 4 to mass of oxygen.

Content suitability

BCIT courses: CHEM 0011