Limiting Reagent (Two Reagents)
Enter the moles and stoichiometric coefficient of two reagents; the smaller mole-to-coefficient ratio wins and is reported as the limiting reagent.
Limitante
—
Limiting reagent: whichever runs out first
When two reagents go into a reaction, the one that runs out first caps how much product you can make. That one is the limiting reagent, and whatever doesn't get used stays behind as excess. Finding it isn't hard. Take the moles you have of each reagent, divide by its stoichiometric coefficient, and the smaller ratio wins. Try it on 2 H₂ + O₂ → 2 H₂O with 4 mol H₂ and 3 mol O₂. You get H₂/2 = 2 and O₂/1 = 3, so H₂ comes in lower and limits the reaction while O₂ is left over. The ceiling is 4 mol H₂O (a 1:1 match with H₂), and 1 mol of O₂ never reacts. Because the limiting reagent fixes the product amount, piling on more of the other one buys you nothing.
Applications
Stoichiometry homework leans on this constantly, and so does batch design in industrial chemistry, where the usual play is to keep the cheap reagent in excess so the expensive one converts all the way. Green chemistry runs the same reasoning to trim waste. In pharmaceutical synthesis a single reagent is often the cost that decides whether a route is even worth running.
FAQ
Why divide moles by coefficient? The coefficient tells you how many moles feed a single "reaction unit". If you hold 4 mol of a reagent whose coefficient is 2, you only cover 2 reaction units; 3 mol with a coefficient of 1 covers 3. Whichever has the lower capacity does the limiting.
Can I just compare masses? No. Comparing masses misses the fact that different substances have different molar masses. Convert everything to moles first, then divide by the coefficients.
What happens to the reagent in excess? It stays unreacted in the mixture and is removed during purification. A lot of the time the excess is on purpose: keep the cheap reagent abundant, and the expensive one reacts all the way through.
Related Tools
Limiting Reagent by Moles
Determines the limiting reagent in a binary reaction from available moles and stoichiometric coefficients.
Reactor Conversion (Batch)
Compute a reactant's conversion, X = (C₀ − C)/C₀·100%, the fraction of reactant consumed in the reaction, from the initial (C₀) and final (C) concentrations. Conversion is the fundamental measure of a chemical reaction's progress: 0% means nothing reacted, 100% that the reactant is exhausted. Together with selectivity and yield, it defines a reactor's performance. Enter the initial and final concentrations.
Buller-Woodrow Loss Factor
Estimates the loss factor of a distribution feeder from its load factor using the empirical Buller-Woodrow relation: loss factor = k × load factor + (1 − k) × load factor squared. The loss factor is the ratio of average loss to peak loss over the period, and it is what turns the instantaneous loss measured at peak hour into energy lost over the month without needing a recorded load curve. Because Joule loss varies with the square of the current, the loss factor always sits below the load factor, and the lower the load factor the lower the ratio between them: at a load factor of 0.20 the loss factor is under half of it, while at 0.80 it sits around 86% of its value. The coefficient k is an input rather than fixed at 0.30, the classic Buller-Woodrow value for distribution networks, because utilities recalibrate k between 0.15 and 0.50 according to the feeder load profile. Enter the load factor for the period and the coefficient k.
Hand-Arm Vibration A(8)
Calculate the normalized hand-arm vibration exposure A(8), A(8) = a_w·√(t ÷ 8), from the resultant acceleration a_w (m/s²) and the exposure time t (hours). The result, in m/s², normalizes the exposure to an 8-hour shift, allowing comparison with the action and tolerance levels. Prolonged exposure to tool vibration (grinders, breakers, chainsaws) causes hand-arm vibration syndrome, with vascular and neurological damage. Enter the resultant acceleration and the exposure time.
Orthodontic Wires Calculator
Estimates orthodontic wires used over treatment months per patient.
Brazilian Pharmacist Fee (CRF)
Computes a referential Brazilian pharmacist service fee per CRF table.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.