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MonoCalc

Reaction Stoichiometry

Chemistry
Use -> or → as reaction arrow. E.g. Fe2O3 + 3CO -> 2Fe + 3CO2

Quick examples:

About This Tool

⚗️ Reaction Stoichiometry Calculator – Moles, Mass & Yield

The Reaction Stoichiometry Calculator is a free online tool that solves the quantitative relationships in any balanced chemical equation. Enter your equation, specify the known amounts of one or more reactants (as mass, moles, solution molarity, or gas volume), and the calculator instantly returns the limiting reagent, theoretical yield, excess reagent amounts, and an optional percent yield — with a full step-by-step dimensional analysis.

Whether you are tackling a university stoichiometry problem, planning a laboratory synthesis, or auditing a chemical process, this tool handles multi-reactant and multi-product systems in seconds.

🔬 What Is Reaction Stoichiometry?

Stoichiometry comes from the Greek stoicheion (element) and metron (measure). In chemistry, reaction stoichiometry uses the mole ratios encoded in a balanced equation to predict how much of every species is consumed or produced when a reaction runs to completion.

For the balanced equation Fe₂O₃ + 3CO → 2Fe + 3CO₂, the coefficients tell us that 1 mole of iron(III) oxide reacts with exactly 3 moles of carbon monoxide to give 2 moles of iron and 3 moles of carbon dioxide. If we start with less CO than that ratio demands, CO is the limiting reagent and the iron yield is capped accordingly.

⚙️ How the Calculator Works

The tool chains four operations automatically:

1. Parse the Balanced Equation

The equation string (e.g. N2 + 3H2 -> 2NH3) is fed to the built-in equation balancer, which extracts each species and its stoichiometric coefficient ν. Reactants are listed on the left of the arrow; products on the right.

2. Convert All Quantities to Moles

Each species row offers four input modes and full unit conversion:

  • Mass (g, kg, mg) → n = mass ÷ M where M is the molar mass
  • Moles → used directly
  • Solution: Molarity + Volume (mL or L) → n = M × V(L)
  • Gas: Pressure, Volume, Temperature → Ideal Gas Law n = PV / RT; supports atm, bar, kPa, mmHg, torr, psi and K, °C, °F
Auto Molar Mass
Molar masses are looked up automatically from IUPAC 2021 standard atomic weights. You can override any value in the molar mass field for non-standard substances.

3. Find the Limiting Reagent

For every reactant r that has a known amount, the calculator computes the reaction extent:

ξᵣ = nᵣ (given) / νᵣ (stoichiometric coefficient)

The limiting reagent is whichever reactant gives the smallest ξ. That minimum value becomes the overall reaction extent ξ, which scales every other species.

4. Scale Products and Excess Reagents

With ξ determined:

  • Moles produced of product p: n_p = ν_p × ξ
  • Moles consumed of reactant r: n_r,consumed = ν_r × ξ
  • Excess remaining: n_r,excess = n_r,given − n_r,consumed
  • Mass of any species: m = n × M

🧪 Practical Examples

Example 1 – Limiting Reagent (Thermite Reaction)

Equation: 2Al + Fe₂O₃ → Al₂O₃ + 2Fe

Given 5.40 g Al (M = 26.98 g/mol) and 8.00 g Fe₂O₃ (M = 159.69 g/mol):

  • n(Al) = 5.40 / 26.98 = 0.2001 mol → ξ(Al) = 0.2001 / 2 = 0.1001 mol
  • n(Fe₂O₃) = 8.00 / 159.69 = 0.0501 mol → ξ(Fe₂O₃) = 0.0501 / 1 = 0.0501 mol
  • Fe₂O₃ is limiting (ξ = 0.0501 mol)
  • Theoretical Fe yield = 2 × 0.0501 × 55.845 = 5.596 g
  • Al excess = 0.2001 − 2 × 0.0501 = 0.0999 mol (2.695 g)

Example 2 – Solution Stoichiometry (Neutralisation)

Equation: HCl + NaOH → NaCl + H₂O

Given 50 mL of 2.0 M HCl and 75 mL of 1.5 M NaOH:

  • n(HCl) = 2.0 × 0.050 = 0.100 mol → ξ = 0.100 mol
  • n(NaOH) = 1.5 × 0.075 = 0.1125 mol → ξ = 0.1125 mol
  • HCl is limiting (ξ = 0.100 mol)
  • NaCl produced = 0.100 mol (5.844 g)
  • NaOH excess = 0.0125 mol (0.500 g)

Example 3 – Percent Yield (Haber Process)

Equation: N₂ + 3H₂ → 2NH₃

If the theoretical yield of NH₃ is 34.06 g but you collect only 29.5 g:

Percent yield = (29.5 / 34.06) × 100 = 86.6%.

💡 Tips and Best Practices

  • Balance first. The tool automatically balances or validates your equation. If it reports a parse error, check your arrow (-> or →) and element capitalisation (e.g. Fe not FE).
  • Provide all reactants for a complete picture. If you only enter one reactant, only that limiting calculation is performed.
  • Use moles mode when you have already converted — it bypasses any molar mass lookup and gives the cleanest step trace.
  • Download the CSV to paste the full mole/mass table into a lab report spreadsheet.
  • For gas-phase species at STP (0 °C, 1 atm), one mole occupies exactly 22.414 L; the table column "STP volume" uses this directly for quick spotchecks.

🔗 Related Chemistry Tools

Pair this calculator with the Chemical Equation Balancer to generate balanced coefficients before entering them here, or use the Molar Mass Calculator to verify formula weights. For gas-phase reactions the Ideal Gas Law Calculator handles PV = nRT interactively, and the Molarity Calculator and Dilution Calculator assist with solution preparation before or after stoichiometric calculations.

Together these tools cover the complete quantitative chemistry workflow: from writing and balancing an equation, through calculating masses and volumes, to reporting theoretical yield and percent yield — all without leaving the browser.

Frequently Asked Questions

Is the Reaction Stoichiometry free?

Yes, Reaction Stoichiometry is totally free :)

Can I use the Reaction Stoichiometry offline?

Yes, you can install the webapp as PWA.

Is it safe to use Reaction Stoichiometry?

Yes, any data related to Reaction Stoichiometry only stored in your browser (if storage required). You can simply clear browser cache to clear all the stored data. We do not store any data on server.

What is reaction stoichiometry?

Reaction stoichiometry is the quantitative relationship between reactants and products in a balanced chemical equation. Using the mole ratios given by the stoichiometric coefficients, you can calculate how much of each substance is consumed or produced when a reaction occurs.

How does this calculator determine the limiting reagent?

For each reactant with a provided amount, the calculator computes the reaction extent ξ = n / ν, where n is the moles of that reactant and ν is its stoichiometric coefficient. The reactant with the smallest ξ is the limiting reagent, because it is consumed first and sets the maximum amount of product that can form.

What input formats are supported for reactant quantities?

You can enter amounts as mass (mg, g, or kg), moles, solution molarity with volume (M and mL/L), or as gas data (pressure, volume, and temperature via the Ideal Gas Law PV = nRT). Each reactant row allows choosing a different input mode.

How is percent yield calculated?

Percent yield = (actual yield / theoretical yield) × 100%. Once the calculator determines the theoretical yield of the target product, you can enter the actual yield you measured in the lab and the calculator will report the percent yield immediately.

What is the reaction extent (ξ)?

The reaction extent ξ (xi) is a single number in moles that quantifies how far the reaction has proceeded. It equals n_limiting / ν_limiting. All other species are then scaled by their own coefficient: moles produced or consumed = ν_i × ξ.

Can I use this tool for solution or gas-phase reactions?

Yes. For solution reactions, enter the molarity (mol/L) and volume (mL or L) of each reagent; the calculator converts to moles automatically. For gas-phase species, enter pressure (atm, bar, kPa, mmHg, torr, or psi), volume, and temperature (K, °C, or °F) and it applies PV = nRT.