# Limiting and Excess Reagents

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Limiting and Excess Reagents
Limiting and excess reactant problems are Stoichiometry problems with two givens, both reactants. Unless one carefully calculates ahead of time the exact amounts of each reactant, one reactant will be used up before the other. This is the limiting reactant (L.R.) The other reactant will not be all used up. This is the excess reactant (X.R.)

Limiting and Excess Reagents
Sample Problem: If I combust 72 grams of Propane (C3H8) in a container holding 45 liters of STP, what is my limiting reactant, what is my excess reactant? How many grams of water are produced? How liters of CO2 are produced? And how much of the excess reactant is left over?

Sample Problem: If I combust 72 grams of Propane (C3H8) in a container holding 45 liters of STP, what is my limiting reactant, what is my excess reactant? How many grams of water are produced? How liters of CO2 are produced? And how much of the excess reactant is left over? Like any stoichiometry problem, you must first have a balanced chemical equation.

Sample Problem: If I combust 72 grams of Propane (C3H8) in a container holding 45 liters of STP, what is my limiting reactant, what is my excess reactant? How many grams of water are produced? How liters of CO2 are produced? And how much of the excess reactant is left over? Next, carry out the three steps of stoichiometry on both givens. (In this problem, it doesn’t matter which product you solve for first, but you must use the same one for each given.)

Sample Problem: If I combust 72 grams of Propane (C3H8) in a container holding 45 liters of STP, what is my limiting reactant, what is my excess reactant? How many grams of water are produced? How liters of CO2 are produced? And how much of the excess reactant is left over?

Sample Problem: If I combust 72 grams of Propane (C3H8) in a container holding 45 liters of STP, what is my limiting reactant, what is my excess reactant? How many grams of water are produced? How liters of CO2 are produced? And how much of the excess reactant is left over? The last step is finding out how much excess reactant is left over. You know how much excess reactant you started with, 72 g C3H8. Using your limiting reactant as your given, carry out the steps of stoichiometry and determine how much of the excess reactant gets used up in the reaction.

Identity of L.R. = O2 Identity of X.R. = C3H8 H2O produced = 28.93 g
Sample Problem: If I combust 72 grams of Propane (C3H8) in a container holding 45 liters of STP, what is my limiting reactant, what is my excess reactant? How many grams of water are produced? How liters of CO2 are produced? And how much of the excess reactant is left over? Answer Summary Identity of L.R. = O2 Identity of X.R. = C3H8 H2O produced = g CO2 produced = L X.R.L.O = g