1. Stoichiometry GPS 13

2. Stoichiometry Example: 2H 2 + O 2 → 2H 2 O Equivalencies: 2 mol H 2 for every 1 mol O 2 2 mol H 2 for every 2 mol H 2 O 1 mol O 2 for every 2 mol H 2 O

3. Stoichiometry Example: N 2 + H 2 → NH 3 - Is the equation balanced? - How many moles of hydrogen gas are there in this equation? - How many moles of ammonia? - How many moles of nitrogen gas?

4. Stoichiometry  Stoichiometry  the term used to describe the quantitative relationships of masses or volumes in a chemical reaction  Using stoichiometry, we can do the following conversions between two different substances:  moles to molesgrams to grams  grams to molesgrams to volume  moles to gramsvolume to volume

5. Mole-Mole conversions Steps 1. Make sure equation is balanced 2. Use coefficients to convert from moles of one substance to moles of another substance

6. Mole-Mole conversions Example:2H 2 + O 2 → 2H 2 O 20 moles of hydrogen gas are combusted to form water. - How many moles of water are formed? - How many moles of oxygen gas are required?

7. Mole-Mole conversions Example:4Fe + 3O 2 → 2Fe 2 O 3 How many moles of oxygen gas are needed to completely react with 85 moles of iron(III)? How many moles of oxygen gas are needed to completely react with 85 moles of iron(III)? How many moles of iron oxide are produced? How many moles of iron oxide are produced?

8. Mass-Mass conversions Steps 1. Make sure equation is balanced 2. Use molar mass and coefficients to convert

9. Mass-Mass conversions Example: 2H 2 + O 2 → 2H 2 O 20.0 grams of hydrogen gas are combusted to form water. - How many grams of water are formed? - How many grams of oxygen gas are required?

10. Mass-Mass conversions Example: 4Fe + 3O 2 → 2Fe 2 O 3 How many grams of oxygen gas are needed to completely react with 85.0 grams of iron(III)? How many grams of oxygen gas are needed to completely react with 85.0 grams of iron(III)? How many grams of iron oxide are produced? How many grams of iron oxide are produced?

11. Mass-Mole / Mole-Mass conversions Example: 2Al + 3H 2 SO 4 → 3H 2 + Al 2 (SO 4 ) 3 How many moles of aluminum are required to completely react with 25.3 grams of hydrogen sulfate? How many moles of aluminum are required to completely react with 25.3 grams of hydrogen sulfate?

12. Mass-Mole / Mole-Mass conversions Example: 2Al + 3H 2 SO 4 → 3H 2 + Al 2 (SO 4 ) 3 How many grams of hydrogen gas are produced when 1.32 moles of aluminum react? How many grams of hydrogen gas are produced when 1.32 moles of aluminum react?

13. Limiting Reactant Limiting reactant (a.k.a. limiting reagent)  the reactant that is completely consumed during the reaction Finding the limiting reactant: 1.Work down to the equivalency line for each reactant 2.The reactant that produces the least amount of product (the one with the smaller number on the equivalency line) is the limiting reagent Excess Reactant(s): - the reactant(s) that is/are left over after the limiting reactant has been completely consumed

14. Limiting Reactant Example: 2H 2 + O 2 → 2H 2 O 12.0 moles of hydrogen gas reacts with 12.0 moles of oxygen gas. Which is the limiting reagent? How many moles of water are made during this reaction? How many moles of water are made during this reaction? Which is the excess reactant? How many moles of excess reactant are left over?

15. Limiting Reactant Example: 2H 2 + O 2 → 2H 2 O 12.0 grams of hydrogen gas reacts with 12.0 grams of oxygen gas. Which is the limiting reagent? How many grams of water are made during this reaction? How many grams of water are made during this reaction? Which is the excess reactant? How many grams of excess reactant are left over?

16. Mass–Volume and Mass–Particle Conversions Steps 1. Make sure all chemical formulas are correct and the equation is balanced 2. If Mass-Volume: Use molar mass, coefficients, and molar volume to convert 3. If Mass-Particle: Use molar mass, coefficients, and Avogadro’s number to convert

17. Mass–Volume and Mass–Particle Conversions If 125 grams of NaN 3 decompose (a) How many liters of nitrogen gas are produced? (b) How many molecules of nitrogen gas are produced? 2NaN 3 → 2Na + 3N 2

18. Volume-Volume Conversions Steps 1. Make sure all chemical formulas are correct and the equation is balanced 2. Use coefficients to convert

19. Volume-Volume Conversions Example:3H 2 + N 2 → 2NH 3 If 15.5 liters of N 2 react with hydrogen gas, how many liters hydrogen gas are needed to react completely?

20. Percent Yield Percent Yield = actual yield x 100 expected yield expected yield  % yield describes the percent of the expected yield that was actually obtained  Actual yield: the amount actually produced when the experiment was performed  Expected yield: the amount that should have been produced (in a “perfect” world)

21. Percent Yield Example: Cu + 2AgNO 3 → 2Ag + Cu(NO 3 ) 2 5.00 g of copper are placed in a solution of silver (I) nitrate containing excess AgNO 3. 15.2 g of silver (Ag) are actually produced during this reaction. What is the percent yield for silver (Ag) for this reaction?

22. Law of Conservation of Mass  You can use the law of conservation of mass to solve for an unknown amount of substance Steps: 1.Find the balanced equation 2.Label grams of each substance 3.Drop down “+” signs and turn the arrow into an equals sign 4.Solve for the unknown mass

23. Law of Conservation of Mass Example:2Na + Cl 2 → 2NaCl If 4.30 grams of sodium react completely with 1.92 grams of chlorine, how many grams of NaCl will be produced?

24. Law of Conservation of Mass Example: Fe reacts completely with MgCl 2. Find the mass of Mg produced. Fe + MgCl 2 → Mg + FeCl 3 Trial Mass of Fe (g) Mass of MgCl 2 (g) Mass of Mg (g) Mass of FeCl 3 (g) 15.62.14.03.7 21.218.6x15.7