1. CHAPTER 12.2 BASIC STOICHIOMETRY
MRS RAGSDALE
CHEMISTRY I

2. MOLAR RATIO REALLY SUPER BIG IMPORTANT!
OBTAINED FROM A PROPERLY BALANCED CHEMICAL EQUATION
BALANCE THE EQUATION WRONG? MOLAR RATIO IS WRONG!
FAIL.
COEFFICIENTS FROM BALANCED EQUATION = MOLAR RATIO

3. MOLAR RATIOS N₂ + 3H₂ → 2NH₃ BASED ON THE COEFFIECIENTS:
Molar Ratio is 1:3:2
FOR EVERY 1 MOLE OF N₂ I WILL NEED 3 MOLES OF H₂
THIS WILL PRODUCE 2 MOLES OF NH₃

4. Moles to Moles N₂ + 3H₂ → 2NH₃
IF YOU HAVE 5 MOLES OF N₂, HOW CAN YOU CONVERT THIS TO NH₃?
N₂ AND NH₃ ARE IN A 1 : 2 RATIO
FOR EVERY 1 MOLE OF N₂, YOU WILL MAKE 2 MOLES OF NH₃
5 MOLES N₂ X = 10 MOLES NH₃

5. Grams to Moles N₂ + 3H₂ → 2NH₃
IF YOU HAVE 25 GRAMS OF N₂, HOW CAN YOU CONVERT THIS TO MOLES OF NH₃?
Remember – to convert grams of a substance into moles, you will need the molar mass (g/mol)
There are 28g of N₂ in 1 mol of N₂
For every 1 mol of N₂ there are 2 moles of NH₃
25gN₂ X X = 1.79 moles NH₃

6. MRS RAGSDALE CHEMISTRY I
12.3 LIMITING REAGENTS
MRS RAGSDALE
CHEMISTRY I

7. WHAT EXACTLY IS A LIMITING REAGENT?
LIMITING REAGENTS – WHATEVER REACTANT THAT YOU RUN OUT OF FIRST
EXCESS REAGENT – WHATEVER REACTANT YOU HAVE LEFT OVER

8. HOW IS A LIMITING REAGENT USEFUL?
YOU CAN PREDICT THE AMOUNT OF PRODUCE YOU CAN EXPECT TO FORM IN A REACTION BASED ON THE LIMITING REAGENT

9. ENOUGH ALREADY… I UNDERSTAND WHAT IT IS BUT HOW THE HECK AM I SUPPOSED TO DO THIS????

10. MRS RAGSDALE’S WAY… 2Cu + S → Cu₂S
LET’S SAY I HAVE 80.0g OF Cu REACTING WITH 25.0g OF S. HOW CAN I FIND OUT WHAT THE LIMITING REAGENT IS?
CONVERT 80.0g OF Cu INTO ?g OF S
AFTER DOING THE MATH I GET 20.2g OF S
USE LOGIC!!! I HAVE 25g OF S AVAILABLE… HOW MUCH DO I ACTUALLY NEED THOUGH?
THAT’S RIGHT! I NEED 20.2g BUT HAVE 25g – S IS IN EXCESS
THAT MEANS THAT Cu IS MY LIMITING REAGENT

11. WHAT IS % YIELD?
WE’RE JUST NOT PERFECT – EVEN THE BEST SCIENTIST WILL LOSE SOME PRODUCT
% YIELD – MEASUREMENT OF HOW MUCH PRODUCT YOU OBTAINED VS HOW MUCH YOU SHOULD HAVE OBTAINED

12. HOW TO CALCULATE % YIELD
STEP 1: THEORETICAL VS ACTUAL
THEORETICAL YIELD: WHAT YOU CALCULATED USING STOICHIOMETRY
ACTUAL YIELD: WHAT YOU PHYSICALLY OBTAINED DOING AN EXPERIMENT
STEP 2: DO THE MATH