1. Limiting/Excess Reagent Stoichiometry
Alyssa Armeni

2. 16.7g of Li is reacted with 30.7g of S, how many grams of Li2S is produced? What is the limiting reagent? What is the excess reagent? How much excess will there be?

3. Draw a complete and Balanced Equation
2Li + S  Li2S

4. Draw a Column for Each Chemical
2Li S
Li2S

5. Write One of the Amounts Given in the Appropriate Column
2Li S
Li2S
16.7g

6. Convert the Amount Given into Moles
2Li S
Li2S
16.7g

7. Find Moles for Each of the Other Chemicals Start with Given Moles In Each Other Column
2Li S
Li2S
16.7g
2.41m

8. Create Fraction to Find Moles Numerator is Coefficient of that Column
2Li S
Li2S
16.7g
2.41m

9. Finish Fraction to Find Moles Denominator is Coefficient of Given Column
2Li S
Li2S
16.7g
2.41m

10. Draw a Line Under Your Work and Write the Second Amount Given Under the Appropriate Column
Li2S
16.7g
2.41m
30.7g

11. Convert the Second Given into Moles
2Li S
Li2S
16.7g
2.41m
30.7g

12. Get Rid of the Bigger Equation Since you can have moles in the same column, you can compare and get rid of the Excess reagent is bigger than .957, therefore the top is bigger and can be crossed out.
2Li S
Li2S
16.7g
2.41m
30.7g X

13. Answer
Since the top number was bigger, the given from that section is the excess reagent. Lithium was on the top so it has the excess amount. That makes the bottom given reagent, Sulfur, the limiting reagent.

14. Repeat the Work Done in the Top Row for the Bottom Row to Answer the Other Questions
2Li S
Li2S
30.7g

15. Find Moles for Each of the Other Chemicals Start with Given Moles In Each Other Column
2Li S
Li2S
.957m
30.7g

16. Create Fraction to Find Moles Numerator is Coefficient of that Column
2Li S
Li2S
.957m
30.7g

17. Finish Fraction to Find Moles Denominator is Coefficient of Given Column
2Li S
Li2S
.957m
30.7g

18. Convert Back to Grams
2Li S
Li2S
.957m
30.7g

19. Verify the Law of Conservation of Mass
2Li S
Li2S
13.3g
30.7g
44.0g
13.3g+30.7
44.0
44.0g = 44.0g

20. Answers 2
There were 44.0g of Li2S. In this reaction only 13.3g of Li were used, subtract this from the given, 16.7g. This gives you an excess amount of 3.4g

21. All Answers Together How many grams of Li2S is produced? 44.0g
What is the limiting reagent?
Sulfur
What is the excess reagent?
Lithium
How much excess will there be?
3.4g