To get the amount of excess reagent left over you must take the
[ Select ]
moles excess reactant you started with
moles excess reactant you used up
moles limiting reactant you started with
and subtract
[ Select ]
moles of excess reagent you used
moles of limiting reagent you used
moles of product you made
.

Question

To get the amount of excess reagent left over you must take the 
[ Select ]
moles excess reactant you started with
moles excess reactant you used up
moles limiting reactant you started with
 and subtract 
[ Select ]
moles of excess reagent you used
moles of limiting reagent you used
moles of product you made
 .

BlackTom AI · Accepted Answer

The question is asking how to determine the amount of excess reagent left after a reaction, and it uses two blanks that are filled from dropdown choices.
First, identify the intended process: to find the remaining amount of the excess reagent, you compare what you started with to what has been consumed of that same reagent in the reaction.
For the first blank, the correct choice is: moles excess reactant you started with. This represents the initial amount of the reagent that is in excess relative to the limiting reagent.
For the second blank, the correct choice is: moles of excess reagent you used. This is the amount of the excess reagent that actually reacted with the limiting reagent to form products (i.e., the portion of the excess that was consumed).
Putting these together, the calculation is: excess leftover = (moles excess reactant you started with) − (moles of excess reagent you used). This difference gives the moles of the excess reagent that remain unreacted after the reaction.
If we had other possible options (for example, references to moles of limiting reagent you started with, or moles of product made), those would not correctly describe the leftover amount of the excess reagent, because:
- Using moles limiting reagent you started with would mix up the concept of which reagent limits the reaction, and wouldn’t quantify unused excess directly.
- Using moles of product made would not reflect how much of the excess reagent was consumed versus remaining, since product formation depends on stoichiometry but doesn’t directly tell leftover quantities of reagents without additional steps.
- Any option referencing subtracting from the wrong quantity would lead to incorrect results, as the arithmetic must compare starting excess to how much of that excess was consumed.
In short, you take the initial amount of the excess reactant, subtract how much of that same reagent was actually used, and the result is the moles of excess reagent that remain unreacted in the mixture.

1A W25 VidQuiz: Limiting Reagents

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