15-­‐10-­‐26 7.3 & 7.4
LIMITING REAGENT
LIMITING REAGENT
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In a chemical reaction, it’s very difficult to get the exact
amount of reactants so that they are both completely used
up. Usually, one of the reactants is used up first.
Limiting Reagent /reactant - The reactant that is
completely used up first. When this runs out, the reaction
stops.
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LIMITING REAGENT
Example 1: Limiting Reagent Problems
Involving Amounts (moles)
¢  Determine the amount of titanium metal produced
when 2.8 mol of titanium (IV) chloride reacts with
5.4 mol of magnesium
Excess Reagent/reactant – Reactant(s) that is/are left
over after the reaction is complete.
The amount of all products in a chemical reaction is
determined by the amount of limiting reagent!
SUMMARY OF STEPS TO SOLVE LR PROBLEMS
INVOLVING MASSES
Step 1: Write a balanced equation for the reaction, listing
the given value(s), required value(s), and molar masses
below the substances being considered in the problem.
¢  Steps 2 – 5: See below
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Step 1: Write a balanced equation listing given value(s) and
required value(s)
Step 2: To determine the limiting reagent, first use the amount of
one reactant to find the stoichiometric amount of the other. It does
not matter which you start with.
Step 3: Use the amount of the limiting reagent to find the amount
of the required substance (MOLE RATIO)
LIMITING REAGENT
Example 2: Limiting Reagent Problems Involving Masses
¢  Methanol (CH3OH) can be made using a synthesis reaction
involving carbon monoxide and hydrogen.
a. What mass of methanol can be produced from 9.80 g of
carbon monoxide and 1.30 g of hydrogen?
b. What mass of excess reagent remains?
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