Stoichiometry Calculator
Universal conversion tool using the Dimensional Analysis method.
ASubstance A (Given)
BSubstance B (Target)
Ready to Solve
Set up your "Given" (A) and "Target" (B) values to see the full dimensional analysis chain.
The Math of Chemistry
Stoichiometry is the toolkit chemists use to predict the future. It's not just about memorizing formulas—it's about mastering Dimensional Analysis to navigate from what you have to what you need.
The Universal Roadmap
The Mole Tunnel
Convert to Moles
You can't cross the bridge without a ticket. Convert your grams, liters, or atoms into **Moles of A**.
The Mole Ratio
The only time you change SUBSTANCES (A to B). Use coefficients from the balanced equation.
Convert to Desired
Now that you are **Moles of B**, convert back out to the unit the question asks for.
Conversion Cheat Sheet
| Unit | To Moles | From Moles |
|---|---|---|
| Mass (g) | ÷ Molar Mass | × Molar Mass |
| Volume (L) | ÷ 22.4 (at STP) | × 22.4 (at STP) |
| Particles | ÷ $6.022\\times10^23$ | × $6.022\\times10^23$ |
Limiting Reagent
Think of making sandwiches. You have 10 slices of bread and 1 piece of cheese. You can only make 1 sandwich. The cheese is the **Limiting Reagent**. The bread is the **Excess Reagent**. Stoichiometry identifies which chemical runs out first.
Unit Trap
The most common mistake is forgetting to check units. Molar Mass is in **grams**. If you are given kg, mg, or lbs, you MUST convert to grams first!
Baking Requires Math
A recipe is just a balanced equation. If a recipe calls for 2 cups flour for 12 cookies, how much flour for 30? Bakers use ratios (stoichiometry) to scale production without ruining the taste.
Medical Dosage
Pharmacists calculate doses based on body weight ($mg/kg$). They convert mass often to ensure safe delivery. An error here is life-threatening, so Dimensional Analysis safety checks are vital.
Industrial Yield
Chemical plants run on "Theoretical Yield". If stoichiometry says 1 ton of ingredients should make 800kg of product, but they only get 700kg, they know their process is inefficient (Percent Yield).
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Frequently Asked Questions
What is Stoichiometry?
Stoichiometry (stoy-kee-ah-met-tree) is the calculation of reactants and products in chemical reactions. It answers the question: "If I have 10g of A, how many grams of B will I produce?" It relies on the Law of Conservation of Mass.
What is Dimensional Analysis?
Also known as the Factor-Label Method, it is a technique where you multiply your starting value by a series of fractions (conversion factors) equal to 1. This canceling-out process ensures your final units are correct.
How do I finding the Mole Ratio?
Look at the coefficients (big numbers) in your balanced chemical equation. Use them to build a fraction. For $2H_2 + O_2 \rightarrow 2H_2O$, the ratio of Hydrogen to Water is $2:2$ (or $1:1$).
Why must I convert to Moles first?
Chemical reactions happen atom-to-atom, not gram-to-gram. Since every atom has a different weight, 10g of Lead has far fewer atoms than 10g of Carbon. The Mole standardizes the count so you can compare them fairly.
What is Avogadro's Number?
$6.022 \times 10^{23}$. This is the number of particles in 1 mole. Use this number whenever you need to convert between Atoms/Molecules and Moles.
When can I use 22.4 Liters?
ONLY when you satisfy two conditions: 1) The substance is a Gas and 2) You are at STP (Standard Temperature and Pressure). If you have a liquid or are at non-standard conditions, you cannot use this conversion.
What is a Limiting Reagent?
It is the ingredient that runs out first. Once the limiting reagent is gone, the reaction stops, no matter how much of the other ingredients (excess reagents) are left. It determines the maximum amount of product you can make.
How do I calculate Percent Yield?
Percent Yield = (Actual Yield / Theoretical Yield) × 100%. Theoretical yield comes from stoichiometry calculations (perfect world). Actual yield comes from measuring the product in a real lab experiment.
How do I find Molar Mass?
Add the atomic masses from the Periodic Table. For Water ($H_2O$): $2 \times 1.008 (H) + 15.999 (O) \approx 18.02$ g/mol.
Can I do gram-to-gram directly?
No single step exists for this. You must always follow the path: Grams A $\rightarrow$ Moles A $\rightarrow$ Moles B $\rightarrow$ Grams B.
What if I have particles of A and want liters of B?
Follow the path: Particles A $\rightarrow$ Moles A $\rightarrow$ Moles B $\rightarrow$ Liters B. The middle step (Mole Ratio) is always the bridge between two different substances.
Why is my answer slightly different?
Rounding errors. Periodic tables vary slightly in precision (e.g., Oxygen is 15.999 vs 16.00). In most classes, these small differences are acceptable.
How does Molarity relate?
Molarity ($M$) is moles per Liter ($mol/L$). It acts as a conversion factor between Volume of Solution and Moles. $Moles = Molarity \times Liters$.
Is Stoichiometry used in real life?
Every day! Pharmacists use it to mix drugs safely. Chefs use it to scale recipes. Engineers use it to fuel rockets. It is the math of mixing things.
What is the Law of Conservation of Mass?
Matter cannot be created or destroyed. The mass of your specific reactants must equal the mass of your products (plus any waste). Stoichiometry proves this mathematically.