Name: _________________________ Partner:______________________ (staple papers
together) STOICHIOMETRY
Web Activity!
Read the short article on the site below and list 3 interesting facts that you learned
in your reading. http://webphysics.iupui.edu/webscience/courses/chem105/goodfor.html
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1. What are three synthetic materials that carpet is made from?
2. Who discovered nylon? What company did he work for?
3. Why is hydrogen cyanide also called Prussic Acid?
http://www.vho.org/GB/Books/thottc/21.html
Find the answers to the following questions on the web!
4. "What is stoichiometry?"
5. In your words, why are stoichiometric calculations important? To whom might
stoichiometric calculations be important?
6. What does the word stoichiometry mean?
Excess and Limiting Reagents – A Short
Explanation!
Chemical reaction equations give the ideal stoichiometric
relationship among reactants and products.
However, the reactants for a reaction in an experiment are not
necessarily an ideal stoichiometric mixture. In a chemical reaction,
reactants that are not use up when the reaction is finished are called excess reagents. The
reagent that is completely used up or reacted is called the limiting reagent, because its
quantity limits the amount of products formed.
Let us consider the reaction between sodium and chlorine. The reaction can be
represented by the equation:
2 Na + Cl2  2 NaCl,
It represents a reaction of a metal and a diatomic gas chlorine. This balanced reaction
equation indicates that two Na atoms would react with two Cl atoms or one Cl2 molecule.
Thus, if you have 6 Na atoms, 3 Cl2 molecules will be required. If there is an excess
number of Cl2 molecules, they will remain unreacted. We can also state that 6 moles of
sodium will require 3 moles of Cl2 gas. If there are more than 3 moles of Cl2 gas, some
will remain as an excess reagent, and the sodium is a limiting reagent. It limits the
amount of the product that can be formed.
Solve This Problem (steps are given to help you)!
Given: Two moles of Mg and five moles of O2 are placed in a reaction vessel, and then
the Mg is ignited according to the reaction
1) Balance the Equation First!
Mg +
O2 
MgO.
2) Convert mols of Mg to mols of MgO (show work)
3) Convert mols of O2 to mols of MgO (show work)
4) Which of the 2 above problems produced the least amount of MgO? This is the
actual amount that can be produced!
5) How many moles of MgO is formed?
6) What is the mass of MgO formed? Convert mols to grams.