1. Limiting Reagent (Reactant)
CHEM 106
Stoichiometry
Limiting Reagent (Reactant)
Dr. Ron Rusay

2. Limiting Reagent An Ice Cream Sundae
The Balanced Equation (Recipe)
The Stuff to be Mixed Together:
??????

3. Limiting Reagent An Ice Cream Sundae
What’s left?
What’s totally consumed?
8 scoops ice cream 6 cherries mL syrup

4. QUESTION
Making a cheese sandwich can be represented by the equation (recipe): Bread (Bd) + Cheese (Ch) → Bd2Ch What would you expect a sandwich to look like?
A B C D A

5. Making a different type of cheese sandwich can be represented by the equation: Bd2 + 2Ch → 2BdCh What would you expect a sandwich of this type to look like?
QUESTION
A B C D D

6. QUESTION
The planned menu at DVC’s soon to open Chemistry Café has a sandwich formula for meat lovers, BdM2Ch, where M is the meat of your choice in the sandwich What might the sandwich likely have in it?
1 pannini, 2 grams of prosciutto, 1 gram of mortadella
2 slices of bread, 2 pieces of salami, 1 piece of swiss cheese
1 slice of bread, 2 pieces of pastrami, 1 piece of asiago cheese
1 loaf of bread, 2 kg of bologna, 1 lb of cream cheese
B is the best answer.

7. QUESTION
The planned DVC menu also has the “Chem Club” with 3 pieces of bread, two thick slices of roast beef, and 2 slices of gruyere cheese. What is the correct formula to place on the printed menu?
Bd2M3Ch2
Bd3M2Ch3
Bd2M2Ch2
Bd3M2Ch2
B is the best answer.

8. QUESTION
The sous chef at the Chemistry Café has a loaf of sourdough bread with 33 slices and a package of cheddar cheese with 15 slices. She is making sandwiches that have 2 pieces each of both bread and cheese. How many sandwiches can she make? 30 16 15 7
B 33/2= /2=7.5 so the max is 7.

9. Limiting Reagent

10. QUESTION Consider the reaction between AB and B2 in the gas phase:
Select the correct statement about this reaction.
The balanced equation for the reaction is AB + B2 → AB3.
B) AB and B2 are present in “stoichiometric” (equivalent molar) amounts at the start of the reaction to consume all of both.
C) AB is the limiting reagent.
D) The product of the reaction is A2B.
Correct Answer: C
Question Number: 11

11. ANSWER Consider the reaction between AB and B2 in the gas phase:
Select the correct statement about this reaction.
The balanced equation for the reaction is AB + B2 → AB3.
B) AB and B2 are present in “stoichiometric” (equivalent molar) amounts at the start of the reaction to consume all of both.
C) AB is the limiting reagent.
D) The product of the reaction is A2B.
Correct Answer: C
Question Number: 11

12. QUESTION

13. ANSWER

14. QUESTION
Global per capita food supply rose from about kcal/day in the early 1960s to over kcal/day by At kcal/person/day, Europe currently has the highest average per capita food supply.
Put another way, shifting the crops used for feed and other uses towards direct human food consumption could increase calories in the food system by 3.89 × 1015 calories, from 5.57 × 1015 to 9.46 × 1015 calories, or a ~70% increase. A quadrillion (1 × 1015) food calories is enough to feed just over 1 billion people a 2700 calories per day diet for a year (which is 985 500 calories per year) [1]. Therefore, shifting the crop calories used for feed and other uses to direct human consumption could potentially feed an additional ~4 billion people.
From 1998 to 2009 (the latest year global food supply data is available from FAO) we saw a 4.4% increase in global calories produced per capita (from 2,713 kcal/capita/day to 2,831) while total agricultural land area dropped by 0.8% (although this may be too small a change in area for this data to reliably detect; see data disclaimers section below). About 32% of the increase came from animal products (mostly meat and milk), with another 27% from vegetable oil and 26% from fruits and vegetables.
- See more at:

15. Answer
B. False
World capacity (kcal) = 3.04 x 1019 J x 1cal/4.184J x 1kcal/1000cal
World capacity (kcal) = 7.26 x 1015 kcal (per year)
World demand = 2700 kcal/ person x 1/day x 365 days/yr = 6.9 x 1015 kcal (per year)
Put another way, shifting the crops used for feed and other uses towards direct human food consumption could increase calories in the food system by 3.89 × 1015 calories, from 5.57 × 1015 to 9.46 × 1015 calories, or a ~70% increase. A quadrillion (1 × 1015) food calories is enough to feed just over 1 billion people a 2700 calories per day diet for a year (which is 985 500 calories per year) [1]. Therefore, shifting the crop calories used for feed and other uses to direct human consumption could potentially feed an additional ~4 billion people.

16. Answer
Do you consume more or less than 2700 Cal/day (kcal/day)?
What is recommended for your age and relative life style?
B. False
Put another way, shifting the crops used for feed and other uses towards direct human food consumption could increase calories in the food system by 3.89 × 1015 calories, from 5.57 × 1015 to 9.46 × 1015 calories, or a ~70% increase. A quadrillion (1 × 1015) food calories is enough to feed just over 1 billion people a 2700 calories per day diet for a year (which is 985 500 calories per year) [1]. Therefore, shifting the crop calories used for feed and other uses to direct human consumption could potentially feed an additional ~4 billion people.

17. Determining a Limiting Reagent
Which one of the reactants has fewer stoichiometrically adjusted moles than the other reactant? The reactant with the smaller value is the limiting reagent.
Calculation:
Divide the mass of each reactant by its respective Molar Mass, and then by its Stoichiometric factor from the balanced equation; compare the results. The lowest one is the limiting reagent.

18. Limiting Reagent Calculation
The reactant present in the smallest molar amount considering stoichiometry limits the mass basis of any reaction.
2 C8H18(l)+ 25 O2(g) CO2(g)+18 H2O(l)
228 g octane / 114 g/mol = 2 mol octane
600. g oxygen / 32 g/mol = mol oxygen
2 mol octane / 2 mol (stoich.) = 1
18.75 mole oxygen / 25 mol (stoich.) = 0.75

19. Mass Effects of the Limiting Reagent
What amount of octane remains unreacted in the reaction of 600. g of O2 with 228 g of octane?
600. g O2 x mol O2 /32g O2 x [2mol C8H18 /25mol O2] x 114 g / mol C8H18 = g C8H18 are reacted
228 g g = 57 g C8H18 remain unreacted

20. QUESTION

21. ANSWER

22. Limiting Reagent / Theoretical Yield
The limiting reagent governs the theoretical yield of products. For the reaction of 228 g of octane with 600. g of oxygen, what is the theoretical yield of carbon dioxide?
2 C8H18(l)+ 25 O2(g) CO2(g)+18 H2O(l)
600. g O2 x mol O2 /32g O2 x 16mol CO2 /25mol O2 x 44g / mol CO2 = 528 g CO2

23. Percent Yield
A reaction was conducted that theoretically would produce moles of quinine, C20 H24 N2 O2 . The actual amount of isolated quinine was 780 mg. What is the percent yield of quinine?
324 g/mol x mol = 81g = 810mg(theoretical)
% Yield = 780 mg/ 810 mg x 100
% Yield = 96%

24. QUESTION
If a reaction produced 2.45g of Ibogaine, C20H26N2O, a natural product with strong promise in treating heroin addiction, and the theoretical yield was 3.05g, what is the % yield?
A) 19.7% B) 39.4% C) 80.3% D) 160.6%

25. ANSWER
If a reaction produced 2.45g of Ibogaine, C20H26N2O, a natural product with strong promise in treating heroin addiction, and the theoretical yield was 3.05g, what is the % yield?
19.7% B) 39.4% C) 80.3% D) 160.6%
% yield = 2.45g / 3.05g x 100
= 80.3%

26. Thoughts to Consider
How much CO2 do you produce per gallon of gasoline (octane, d= 0.70 g/ml) when gasoline is combusted?
How much CO2 do you personally produce from driving every week?…. every month? …. every year? ….from other uses and sources?
“Man-made” CO2 directly relates to global warming. How does “man-made” CO2 relate to jobs and the global economy?
Why do people in nations in the EU, the U.S., China, Japan & others produce tons more of CO2 than people in under developed or developing nations?
Global Warming Questions