1. Stoichiometry

2. What is stoichiometry? Involves the mass relationships between reactants and products in a chemical reaction ▫Based on the law of conservation of mass ▫MUST start with a balanced equation

3. Why is stoichiometry important? ▫Cost reduction/efficiency in production ▫Pharmaceutical (getting the right amount makes a difference)

4. Equations are the recipes that tell chemists what amounts of reactants to mix and the amounts of products to expect. ▫stoichiometry helps chemists manufacture products economically and profitably.

5. Balanced equations and stoichiometry Balanced equations give the relative number of moles of reactants and products Example: 2H 2 + O 2 → 2H 2 O ▫2 moles of hydrogen ▫1 mole of oxygen ▫Ratio =2 mol H 2 :1 mole O 2

6. Mole Ratio Use the coefficients in conversion factors called mole ratio This allows you to calculate mass of different compounds!! Example: N 2 + 3H 2 → 2NH 3 ▫What is the ratio of H 2 and NH 3 ?

7. N 2 + 3H 2 → 2NH 3 How many moles of hydrogen is needed to get 312 mol NH 3 ?

8. Solving Stoichiometry Problems 1.Start with a balanced equation 2.Identify given and wanted information 3.Change grams to moles if necessary 4.Use mole ratios from balanced equations 5.Convert back to grams (if necessary)

9. Practice Problems mole-mole calculations H 2 O 2  H 2 O +O 2 ▫If you start with 1.34 mol H 2 O 2 ▫A) how many moles of O 2 are produced? ▫B) How many moles of H 2 O are produced?

10. Think about it… In all of the problems we’ve done so far, we’ve started out in units of moles. Why are mole/mole problems impractical in a laboratory setting?

11. Example mass-mole H 2 + Cl 2 → 2 HCl How many moles of HCl can be made from 27.3 g of chlorine gas?

12. Example: mass-mass caculations *Anytime you are starting with or ending with mass, you will need to use molar mass to convert between grams and moles What mass of NH 3 can be made from 1221 g of H 2 ? N 2 + 3H 2 → 2NH 3

13. Example: mass-mass How many grams of Al are needed to completely react with 135 g of Fe 2 O 3 ? Fe 2 O 3 + 2Al → 2Fe + Al 2 O 3

14. Example: How many grams of Al 2 O 3 can be made from 23.6 g of Aluminum? Fe 2 O 3 + 2Al → 2Fe + Al 2 O 3

15. Example: mass-mass How many grams of Fe 2 O 3 are needed to completely react to form 475 g Fe? Fe 2 O 3 + 2Al → 2Fe + Al 2 O 3

16. Stoichiometry Island Diagram Mass Particles Volume Mole Mass Volume Particles Known Unknown Substance A Substance B 1 mole = molar mass (g) Use coefficients from balanced chemical equation 1 mole = 22.4 L @ STP 1 mole = 6.022 x 10 23 particles (atoms or molecules) 1 mole = 22.4 L @ STP 1 mole = 6.022 x 10 23 particles (atoms or molecules) 1 mole = molar mass (g) (gases)

17. Stoichiometry Particles and Liters

18. Stoichiometry Can be expanded to any unit of measurement that is related to a mole. Remember, you always want to 1.get your given into moles, 2.use mole ratio (coefficients from balanced equation) 3. then convert it to the units you need your answer to be in

19. Review How many grams of water can be prepared from 8.00 grams of hydrogen at standard conditions? 2 H 2 (g) + O 2 (g) → 2 H 2 O

20. Review 6 A chemist performs the synthesis of sodium chloride from its elements. The chemist begins with 46 grams of sodium. How many moles of chlorine are needed? 2 Na + Cl 2 → 2 NaCl

21. Volume (liters) At STP (standard temperature pressure): ▫1 mole of gas occupies 22.4 L of space ▫1 mole =22.4 L (conversion factor). ▫STP is 1 atm (pressure) and 273 K (temperature) ▫We will assume all conditions are STP

22. In the formation of carbon dioxide how many liters of carbon monoxide, CO, are needed to react completely with 1.50 mole of oxygen gas at STP? 2 CO (g) + O 2 (g) → 2 CO 2 (g)

23. How many Liters of oxygen are required to burn 43.1 liters of ethane gas, C 2 H 6 at standard conditions? 2 C 2 H 6 (g) + 7 O 2 (g) → 4 CO 2 (g) + 6 H 2 O (g)

24. At standard conditions, how many liters of carbon dioxide, CO 2, will be formed by the combustion of 182 grams of propane, C 3 H 8 ? C 3 H 8 + 5 O 2 → 3 CO 2 + 4 H 2 O

25. Particles Avogadro’s number! What exactly is a mole? A mole is a unit of measurement (like a dozen) that indicates an amount 6.02 x 10 23 1 mole = 6.02 x 10 23 representative particles (r.p.) -molecules/particles/atoms

26. C 3 H 8 + 5 O 2 → 3 CO 2 + 4 H 2 O How many molecules of Oxygen are needed to produce 1.2 moles of of CO 2 ?

27. 2 Na + Cl 2 → 2 NaCl How many atoms of NaCl are produced with 26 grams of Na?

28. Limiting Reactants & Percent Yield Chapter 9 Section 3 Chapter 9, Section 2

29. Limiting Reactants  Reactants are seldom present in amounts that are equal to the mole ratio in the balanced equation  If one reactant runs out before the other, it is said to be the limiting reactant  Limiting reactant = limits the amount of product that can be formed  The other reactant is the excess reactant

30. Limiting Reactants o Limiting reactant: the reactant that controls the quantity of product that can form in a chemical reaction o Excess reactant: the reactant(s) that is more than enough to react with the limiting reagent

31. Limiting Reagent (with grilled cheese) 1 Cheese + 2 pieces of bread → 1 Grilled Cheese + → How many grilled cheese sandwiches (product) can you make? Limiting Reagent: Excess Reagent:

32. Limiting Reagent (with real chemistry!) 3 H 2 + 2 N → 2 NH 3 How many ammonia molecules can you make? Limiting Reagent: Excess reagent:

33. How do we calculate using stoich?? 1.Calculate for each reactant given to determine how much product (moles, liters, particles, grams) would be produced. 2.Compare, the reactant that produces the least amount of product is the limiting reagent.

34. Practice ** 2Na (s) + Cl 2(g)  2NaCl (s) Suppose 6.70 mol of Na Reacts with 3.20 mol of Cl 2 What is the limiting reagent?

35. Limiting Reactants - Example Zn + 2HCl → ZnCl 2 + H 2 Given: 0.23 mols Zn ; 0.60 mols HCl Which is the limiting reactant? -Use the mole ratio to determine which will produce the most H 2 0.23 moles Zn = 0.23 moles H 2 0.60 moles HCl = 0.30 moles H 2

36. Example: PCl 3 + 3H 2 O → H 3 PO 3 + 3HCl Identify the limiting reactant and the amount of H 3 PO 3 that will form if 225 g of PCl 3 is mixed with 123g of H 2 O.

37. Example: ** 2Cu (s) + S (s)  Cu 2 S (s) a.What is the limiting reagent when 80.0g of Cu reacts with 25.0g of S? b.What is the maximum number of grams of Cu 2 S that can be formed?

38. Theoretical yield: The maximum amount of product that could be formed from given amounts of reactants (this is the calculated amount!) Actual Yield: the amount of product when the reaction is carried out in the laboratory (often less than the theoretical yield)

39. Where Do products Get Lost? Products lost ▫Side reactions ▫Purification techniques ▫Gases hard to collect

40. The ratio of the actual yield to the theoretical yield expressed as a percent **must be in the same units for this to work. % Yield = actual yield x 100 theoretical yield (stoich) Percent yield

41. C ₇ H ₈ + HNO ₃  C ₇ H ₇ NO ₂ + H ₂ O 1.What is the theoretical yield of C 7 H 7 NO 2 if 550 grams of C 7 H 8 is reacted with excess nitric acid? 1.What is the percent yield if 305 grams was actually produced?

42. CaCO 3(s)  CaO (s) + CO 2(g) a. What is the theoretical yield of CaO if 24.8g of CaCO 3 is heated? b. What is the percent yield if 13.1g CaO is produced?