Stoichiometry

The "Railroad Tracks" Method

Stoichiometry can feel overwhelming at first, but once you learn the “railroad tracks” method, it becomes much easier. This method is a visual and organized way to do dimensional analysis, where you line up your conversions step-by-step like train cars on tracks.

What Is It?

The "railroad tracks" method is a tool for keeping units and numbers organized while solving stoichiometry problems. You start with what you're given and multiply by a series of conversion factors—each one moving you closer to the unit you're trying to find.

Example Problem:

How many grams of water (H₂O) are produced from 4.00 grams of hydrogen gas (H₂)?

Balanced equation:
2 H₂ + O₂ → 2 H₂O

Step-by-Step Using Railroad Tracks:

1. Start with what you're given:

4.00 g H₂ |

2. Convert grams to moles using molar mass of H₂ (2.02 g/mol):

4.00 g H₂ 1 mol H₂
| —
2.02 g H₂

3. Use the mole ratio from the balanced equation:

4.00 g H₂ 1 mol H₂ 2 mol H₂O
| — | —
2.02 g H₂. 2 mol H₂

4. Convert moles of H₂O to grams using molar mass (18.02 g/mol):

4.00 g H₂ 1 mol H₂ 2 mol H₂O 18.02 g H₂O
| — | — | —
2.02 g H₂. 2 mol H₂ 1 mol H₂O

Multiply across:

4.00 g H₂ 1 mol H₂ 2 mol H₂O 18.02 g H₂O
| — | — | — = 35.68 grams of H₂O
2.02 g H₂. 2 mol H₂ 1 mol H₂O

Another way of looking at this is:

4.00 × (1 / 2.02) × (2 / 2) × 18.02 = 35.68 grams of H₂O

Why It Works

This method keeps your work clean and helps prevent mistakes. Units cancel out as you go, and you’re left with the unit you’re solving for—usually grams or moles.

Whether you're just starting chemistry or reviewing for a test, railroad tracks are a great way to build confidence and accuracy in stoichiometry.