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Concept module

Limiting Reagent and Leftover Reactants

Use one recipe bench to see which reactant caps the output first and why the other reactant can remain in excess.

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A caps first

Open the run where A sets the batch cap and B is left over.

B caps first

Flip to a run where B runs out first and A stays on the bench.

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Starter track

Step 2 of 30 / 3 complete

Stoichiometry and Yield

Earlier steps still set up Limiting Reagent and Leftover Reactants.

1. Stoichiometric Ratios and Recipe Batches2. Limiting Reagent and Leftover Reactants3. Percent Yield and Reaction Extent

Previous step: Stoichiometric Ratios and Recipe Batches.

Start from track beginning

Why it behaves this way

Explanation

Limiting reagent makes more sense when the lower recipe-supported cap stays visible beside the actual supply trays. This bench keeps both reactant bins, the recipe card, and the leftover readout together so the limiting step never turns into hidden algebra.

The limiting reagent is just the reactant that can support fewer complete recipe batches. The other reactant is excess, so some of it remains once the last full batch finishes.

Key ideas

01Each reactant supply supports its own possible batch count when you divide by the recipe packets required per batch.
02The smaller batch count sets the theoretical output because the reaction cannot finish more full batches than that.
03Leftover reactant belongs to the excess side, not to the limiting side.

Frozen walkthrough

Step through the frozen example

Frozen walkthrough
Read the lower cap directly from the recipe bench.

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Frozen valuesUsing frozen parameters

Which supply is limiting in the 8 A, 15 B run, and what remains after the full-yield reaction?

Reactant A packets

reactantAAmountValue

Reactant B packets

reactantBAmountValue

B per batch

recipeBValue

1. Convert each supply into possible batches

A can support 8 / 2 = 4 full batches, while B can support 15 / 3 = 5 full batches.

2. Read the lower cap as the limiting reagent

Because four batches is the smaller cap, A is the limiting reagent and the theoretical output is four batches.

3. Spend the recipe and read what stays behind

Four full batches spend 12 B packets, so 3 B packets remain while A is fully used.

Limiting side

A limits; 3 B packets remain.
The limiting reagent is the first supply to run out once the recipe spends complete batches only.

Common misconception

The reactant with the smaller raw packet count must always be the limiting reagent.

Limiting depends on the recipe card as well as the raw supply counts.

A larger raw count can still be limiting if each batch consumes that reactant more heavily.

Mini challenge

Make one reactant cap the recipe while the other clearly stays in excess.

Make a prediction before you reveal the next step.

Decide which supply must have the lower recipe-supported batch count before you move the sliders.

Check your reasoning against the live bench.

The limiting reagent is whichever side supports fewer complete batches on the recipe card.
Once you compare both batch caps on the same bench, the leftover story follows automatically from the excess side.

Quick test

Reasoning

Question 1 of 2

Answer from the visible batch caps and leftovers, not from a memorized slogan.

On a 2:3 recipe with 8 A and 15 B, which supply is limiting?

Use the live bench to test the result before moving on.

Accessibility

The simulation shows two reactant supply bins, one product tray, and a recipe card that states how many packets of A and B one full batch needs.

A readout card reports the current recipe, the maximum possible batches, which supply is limiting, the actual output, and how much of each reactant is left after the run.

Graph summary

One graph scans possible batches against the A supply, a second scans possible batches against the B supply, and a third keeps actual output against the theoretical product marker as percent yield changes.

The limiting cue and leftover readout stay tied to the same recipe bench instead of leaving the particle view.