1. Limiting Reactant
Videodisk 4
Unit 8 Lesson 2

2. Limiting Reactants Limiting Reactant - reactant you run out of first
Reactant in Excess - reactant you have more than enough of
To determine the limiting reactant, find the number of moles of each reactant and then divide by their respective coefficients
Paperclip Demo
Envelopes of paperclips
Give students the formula of the molecule and have them build as many as possible of that molecule. Discuss the limiting reactant and the reactant in excess.

3. Example Problem
What is the limiting reactant if you have 5.0g H2 and 10.0g O2?
2H2 + O2 → 2H2O
Meaning for every 2 moles of H2 you need 1 mole of O2
5.0g H2 (1 mole H2/2.016g H2) = 2.5 moles of H2
10.0 g O2(1mole O2 /32.00g O2) = moles O2

4. Continued: divide each by their coefficients
O2 has the smaller value, so oxygen must be the limiting reactant

5. Example Problem 2Na + Cl2  2NaCl
Identify the limiting reactant and the mass of sodium chloride produced when 1.7 g of sodium reacts with 2.6 L of chlorine gas at STP.
2Na + Cl2  2NaCl
To identify the limiting reactant:
1.7 g Na x 1 mol Na/22.99 g Na = mol Na
Divide by Na coefficient: mol Na/2 mol = 0.037
2.6 L Cl2 x 1 mol Cl2/22.4 L Cl2 = mol Cl2
Divide by Cl2 coefficient: 0.12 mol Cl2/1 mol = 0.12

6. Na is limiting because less NaCl could be made from 1. 7 g of Na (0
Na is limiting because less NaCl could be made from 1.7 g of Na (0.037) than 2.6 L Cl2 (0.12)
To determine NaCl produced: go back to mol Na and complete stoichiometry
0.074 mol Na x (2 mol NaCl/2mol Na) x g NaCl/molNaCl
= 4.3 g NaCl

7. Barium is limiting reactant
Sample Problem
When 22.6 g of barium and 4.2 g of nitrogen gas react, which is the limiting reactant and how many grams of barium nitride are produced?
3Ba + N2  Ba3N2
Barium is limiting reactant
24.2 g Ba3N2