Day 44 Chapter 9 Notes (Stoichiometry)
Stoichiometry: The study of ______of materials that are
______and ______in chemical reactions.
v Stoichiometry uses chemical equations to solve problems or make quantitative predictions.
Three new concepts:
Mole Ratio: Using a balanced equation to convert moles of one formula to another.
Limiting Reactant: (also called Limiting Reagent)
A chemical reaction stops if you run out of one of the reactants.
VERY IMPORTANT!!
Predictions or “theoretical yields” are determined by the ______
% Yield: Comparing the actual experimental result to the amount predicted.
Review (ChemA) Please schedule after-school help if you need practice.
· Chapter 3
o Use unit-conversion/factor-label method to solve problems.
· Chapter 6
o How to write correct formulas.
§ Calcium chloride: Ca2+ + Cl-1 → ______
§ Sodium carbonate: Na+ + CO32- → ______
§ Aluminum nitrate: Al3+ + NO3-1 → ______
§ Sulfur dioxide: ______
· Chapter 7
o Mole Concept. (Convert between mass, volume, particles)
SO2
Chapter 8
o Balance chemical equations.
____N2 + ____H2 → ____NH3
The coefficients in a balanced equation can represent moles, molecules, or volumes of gases at STP.
The Mole Ratio Concept (Use coefficients from a balanced equation)
Coefficients can represent moles, molecules, or volumes of gases at STP.
It seems to work best to write this as a fraction like this:
When Solving a Problem using stoichiometry:
- Always start with a balanced ______
- Convert given ______to moles.
- Use the ______to convert moles of given to moles of what you want.
- ______to desired product in terms of mass, volume, or number of particles.
Problem 1: Suppose you wanted to make some nitrogen triiodide.
N2 + I2 à NI3
v How many moles of nitrogen do you have?
Given: Want:
14.0 g N2 = ______mol N2
v How many moles of iodine will react with the given nitrogen?
Given: Want:
3.01 x 1023 molecules N2 = ______mol I2
v Predict how many moles of nitrogen triiodide, NI3, are theoretically produced from given N2.
Given: Want:
44.8 L N2 = ______mol NI3
v Convert moles NI3 to grams of NI3 and you have a theoretical yield. Just don’t blow yourself up!
Given: Want:
0.04 mol NI3 = ______g NI3
Limiting Reactant Concept
A reaction stops when you use up one of the reactants. Therefore, the limiting reactant determines the theoretical yield.
· The reactant you use up is called the “limiting reactant”.
· The reactant you have left over is called the “excess reactant”.
Everyday example:
Suppose you worked as a student aide making booklets for the office. A booklet consists of 10 pages of paper, 3 staples, and 1 cover. In the supply closet you find that you have 500 sheets of paper, 240 staples, and 25 covers.
10 pages + 3 staples + 1 cover → booklet
Given (500 pages) (240 staples) (25 covers) ??
How many booklets can you make? Justify your answer.
Chemistry example:
The Haber process is the most widely used chemical process in the world. It is the production of ammonia, NH3 from nitrogen and hydrogen.
v You are in charge of the chemical plant and know that you can get nitrogen from the air but hydrogen costs about $15 per Liter.
Hydrogen gas should be the limiting reagent because it ______
v Write a balanced chemical equation for the production of ammonia:
N2 + H2 → NH3
v If you had 12 moles of N2 and 30 moles of H2, how many grams NH3 can you make?
Determine limiting reactant: Given Ideal (from Bal. Eqn.)
mol H2 30 2.5 mol H2
mol N2 12 1 mol N2
Use limiting reactant to calculate theoretical yield of NH3
Given: Find:
30 mol H2 = ______g NH3
% Yield Concept
v Suppose you complete the reaction above and get an actual yield of 285 g for NH3. Based on the theoretical yield calculated above, what is the % yield for this reaction?
Assignment:
Vocabulary Builder: Please define the following terms in your own words.
Stoichiometry:
Mole:
Reactants:
Products:
Limiting reagent:
Excess reagent:
Theoretical yield:
Actual yield:
Percent yield:
Mass-mass calculations: