Limiting Reagents

Steps to finding the GFW

Before you know how to solve limiting reagents problems, it is important that you know how to find the molar mass (GFW) of a given compound.

You can round all atomic masses to a whole number, except for Chlorine's, which stays and is completely rounded to 35.5 g/mol.

Here are two example problems to help you get adjusted:

1. C₄H₁₀S and O₂

Multiply the molar mass of each atom by the number of compounds it contains (ex. multiply carbon's atomic mass by 4 or hydrogens atomic mass by 10)

C = 12 (x 4)

H = 1 (x 10)

S = 32 (x 1)

GFW of C₄H₁₀S = 90 g/mol

O = 16 (x 2)

GFW of O_{2 = 32 g/mol}

So, the GFW of C₄H₁₀S is 90 g/mol, while the GFW of O_{2 is 32 g/mol.}

2. CH_{4 and Cl2}

C = 12 (x 1)

H = 1 (x 4)

GFW of CH_{4 = 16 g/mol}

Cl = 35.5 (x 2)

GFW of Cl_{2 = 72 g/mol}

So, the GFW of CH_{4 is 16 g/mol and the GFW of Cl2 is 72 g/mol.}