1. Chemistry 103 Lecture 15

2. Outline I. Chemical Reactions - balancing (review) II. Stoichiometry - Limiting Reactant III. Classification of Reaction Types

3. Molar Mass from Periodic Table Molar mass Is the atomic mass expressed in grams

4. Avogadro’s Number Solution = 6.022 x 10 23 Avogadro’s number is equal to 1 mole Makes working with large numbers easier

5. The Mole Molar mass 1 mole 6.022 x 10 23 Mass in grams Individual particles

6. Concept Review Do 7.0g of CO and 7.5 g of C 2 H 6 contain the same number of C atoms? (Prove your answer mathematically) A. YESB. NO

7. Chemical Reaction In a chemical reaction, Old bonds are broken and new bonds are formed Atoms in the reactants are rearranged to form one or more different substances Fe and O 2 form rust (Fe 2 O 3 )

8. Chemical’s Shorthand - Chemical Rxn Fe (s) + O 2 (g) --------> Fe 2 O 3 (s) 2Fe(s) + O 2 (g) --------> Fe 2 O 3 (s) 4Fe(s) + O 2 (g) --------> 2Fe 2 O 3 (s) 4Fe(s) + 3O 2 (g) --------> 2Fe 2 O 3 (s) BALANCED!!!!!

9. Balancing Practice Li 3 N(s) -------> Li(s) + N 2 (g) Mg + H 3 PO 4 ------> Mg 3 (PO 4 ) 2 + H 2 MgCl 2 + AgNO 3 ------> Mg(NO 3 ) 2 + AgCl

10. Stoichiometry Chemical Stoichiometry: using mass and quantity relationships among reactants and products in a chemical reaction to make predictions about how much product will be made.

11.  We can read the equation in “moles” by placing the word “mole” or “mol” between each coefficient and formula. 4Fe(s) + 3O 2 (g) 2Fe 2 O 3 (s) 4 mol Fe + 3 mol O 2 2 mol Fe 2 O 3 Moles in Equations

12. Mole to Mole problems Using the balanced chemical reaction, how many moles of O 2 will react with 4.28 moles of CS 2 to produce CO 2 and SO 2 ? CS 2 + O 2 ------> CO 2 + SO 2 (unbalanced)

13. Mole to Mole problems When 4.28 moles of CS 2 reacts according to the balanced chemical equation below, how many moles of CO 2 will be produced? CS 2 + 3O 2 ------> CO 2 + 2SO 2

14. Mole to Mole problems When 4.28 moles of CS 2 reacts according to the balanced chemical equation below, how many moles of SO 2 will be produced? CS 2 + 3O 2 ------> CO 2 + 2SO 2

15. Reaction Interpretation Using the balanced chemical reaction, how many moles of O 2 will react with 4.28 moles of CS 2 to produce CO 2 and SO 2 ? CS 2 + 3O 2 ------> CO 2 + 2SO 2 BEFORE AFTER

16. Moles-to-Grams or Grams-to-Mole

17. Chemical Stoichiometry 2H 2 + O 2 ----> 2H 2 O mole to mole comparisons: How many moles of O 2 are needed to produce 1.39 moles of H 2 O?

18. Chemical Stoichiometry 2H 2 + O 2 ----> 2H 2 O mole to gram or gram to mole comparisons: How many moles of O 2 are needed to produce 7.4g of H 2 O?

19. Chemical Stoichiometry 2H 2 + O 2 ----> 2H 2 O mole to mole comparisons: How many moles of O 2 are needed to exactly react with 4.28 moles of H 2 ?

20. Chemical Stoichiometry 2H 2 + O 2 ----> 2H 2 O mole to gram or gram to mole comparisons: How many moles of O 2 are needed to exactly react with 12.4g of H 2 ?

21. How many grams of O 2 are needed to produce 0.400 mol Fe 2 O 3 ? 4Fe(s) + 3O 2 (g) 2 Fe 2 O 3 (s) A) 38.4 g O 2 B) 19.2 g O 2 C) 1.90 g O 2 Grams-to-Mole

22. “gram to gram” calculations

23. The reaction between H 2 and O 2 produces 13.1 g water. How many grams of O 2 reacted? 2H 2 (g) + O 2 (g) 2H 2 O(g) Plan: g H 2 O mole H 2 O mole O 2 g O 2 Calculating the Mass of a Reactant

24. The reaction between H 2 and O 2 produces 13.1 g water. How many grams of O 2 reacted? 2H 2 (g) + O 2 (g) 2H 2 O(g) Before: x g After: 13.1 g Plan: g H 2 O mole H 2 O mole O 2 g O 2 Calculating the Mass of a Reactant

25. Mass calculations How many grams of CS 2 are needed to completely react with 6.0g of O 2 according to the following reaction? CS 2 + 3O 2 ------> CO 2 + 2SO 2

26. “gram to gram” continued…. One way to remove gaseous carbon dioxide from the air in a spacecraft is to let canisters of solid lithium hydroxide absorb it according to the following reaction: 2LiOH(s) + CO 2 (g) ------> Li 2 CO 3 (s) + H 2 O(l) How many grams of LiOH must be used to produce 10.0g of Li 2 CO 3 ?

27. Learning Check Acetylene gas C 2 H 2 burns in the oxyacetylene torch for welding. How many grams of C 2 H 2 are burned if the reaction produces 75.0 g CO 2 ? 2C 2 H 2 (g) + 5O 2 (g) 4CO 2 (g) + 2H 2 O(g) A) 88.6 g C 2 H 2 B) 44.3 g C 2 H 2 C) 22.2 g C 2 H 2

28. Chemical Reactions Limiting Reactant & Percent Yield

29. Limiting Reactant A limiting reactant in a chemical reaction is the substance that: Is used up first Stops the reaction Limits the amount of product that can form

30. Reacting Amounts In a table setting, there is 1 plate, 1 fork, 1 knife, and 1 spoon. How many table settings are possible from 5 plates, 6 forks, 4 spoons, and 7 knives? What is the limiting item?

31. Reaction Equivalent 1plate + 1fork + 1knife + 1spoon ----> 1place setting BEFORE 5 6 7 4 0 AFTER 1 2 3 0 4 LR

32. Reacting Amounts In a table setting, there is 1plate, 2 forks, 1 knife, and 1spoon. How many table settings are possible from 5 plates, 6 forks, 4 spoons, and 7 knives? What is the limiting item?

33. Reaction Equivalent 1plate + 2fork + 1knife + 1spoon ----> 1place setting BEFORE 5 6 7 4 0 AFTER 2 0 4 1 3 LR

34. Limiting Reactants When 4.00 mol H 2 is mixed with 2.00 mol Cl 2,how many moles of HCl can form? H 2 (g) + Cl 2 (g)  2HCl (g) 4.00 mol 2.00 mol ??? Mol STEPS: Calculate the moles of product from each reactant, H 2 and Cl 2. The limiting reactant is the one that produces the smallest amount of product.

35. Checking Calculations InitiallyH 2 4.00 mol Cl 2 2.00 mol 2HCl 0 mol Reacted/ Formed -2.00 mol +4.00 mol Left after reaction 2.00 mol Excess 0 mol Limiting 4.00 mol

36. Limiting Reactant If 4.80 grams Ca mixed with 2.00 grams N 2, which is the limiting reactant? 3Ca(s) + N 2 (g)  Ca 3 N 2 (s)

37. Limiting Reactants Using Mass Calculate the mass of water produced when 8.00 g H 2 and 24.0 g O 2 react? 2H 2 (g) + O 2 (g) 2H 2 O(l)