1. Mole Ratios Limiting Reagent % Yield Gas Stoichiometry

2. Stoichiometry
Chemistry is often called the science of proportions; Kitchen Chemistry/Recipes
Stoichiometry : the study of chemical quantities based on a balanced equation.

3. Stoichiometry
Measureable and Quantitative relationship between reactants and products
So, a chemical reaction takes place:
Identify:
Classification:
Law of Conservation of Mass:

4. You Must Remember:
To BALANCE every equation

5. Remember the mole??
Quantities in chemical equations are counted as moles.

7. Chemical Ratios
Substances in a balanced equation are always in a given proportion to each other.
1N2 + 3H2  2NH3
The proportions can be written as ratios.

8. Mole Ratios These proportions are called “mole ratios”.
1N2 + 3H2  2NH3
For Every
There are/is
Creating ratio
1N2
3H2
1mol N2/3mol H2
2NH3 N2

9. Mole Ratios
What is the mole ratio found in the balanced equation below?
N2O5  NO2 + O2

10. The “Given”
If 2 moles of N2O5 is reacted, how many moles of NO2 will be formed?
There is always a given in a stoichiometry problem that includes
A numeric value (2)
A metric unit (moles)
A substance (N2O5)

11. Mole-Mole Calculation
If 2 moles of N2O5 is reacted, how many moles of NO2 will be formed?
1) 2 mol N2O5 x mole ratio (which one?)
2) 2 mol N2O5 x
mol N2O5 (cancel the given)
3) 2 mol N2O5 x mol NO2 (write what you want)
mol N2O5

12. Mole-Mole Calculation
1- Balance the equation
2- Write down your given
3- Use conversion factors to convert moles
(use the coefficients here)
We call this the Heart
of the equation

13. Heart of Every Equation
mol unknown =
mol given

14. Mole-Mole Calculations
Coef mol
_______________________
mol given
coef mol unknown
coef mol given

15. Mole-Mass Problem mol A 1 mol B
How much (mass) B can be formed from a given number of moles of A?
mol A x mol B x g B = g B
mol A mol B
1) The mol-mol ratio comes from the equation
2) The mol-mass ratio comes from the periodic table

16. C3H8 + 5O2  3CO2 + 4H2O
5.4 moles of propane (C3H8) is converted into how many moles of carbon dioxide?

17. Mole-Mass Calculations
____________________________________
Molar mass
(g)
mol given
coef mol unknown
coef mol given
1 mol

18. 4NH3 + 5O2  6H2O + 4NO
How many grams of H2O are produced if 1.9 mol of NH3 are combined with excess oxygen?

19. Mass-Mole Problem
How many moles of B can be formed from a given mass of A?
g A x 1 mol A x mol B x = mol B
g A mol A
1) The mol-mol ratio comes from the equation
2) The mol-mass ratio comes from the periodic table

20. Mass-Mole Calculations:
mol given mol coef mol unknown
__________________________________
molar mass coef mol given
(g)

21. Fe2O3 + 3CO -> 2Fe + 3CO2
How many grams of carbon dioxide are produced with 2 moles of iron (3) oxide?

22. Mass-Mass Problem
How much (mass) B can be formed from a given mass of A?
g A x 1 mol A x mol B x g B = g B
g A mol A mol B
1) The mol-mol ratio comes from the equation
2) The mol-mass ratio comes from the periodic table

23. Mass-Mass Calculations:
g-given mol coef mol molar mass
unknown (g)
____________________________________
molar mass coef mol mol
given

24. Fe2O3 + 3CO -> 2Fe + 3CO2
How many grams of iron would be produced using 25 grams of iron (3) oxide?

26. Mole Ratios Limiting Reagent-LR % Yield Gas Stoichiometry

27. Limiting Reagent
Limiting reagent = a reactant that limits the amount of product that can be made
It can also be thought of as a limiting ingredient

28. Limiting Reagent Recipe: peanut butter and jelly sandwich
2Br + 3Pb + 2Je  1 Sa
3 ingredients necessary to produce one sandwich
Could any one of these run
out before the other two?

29. Excess Reagents Excess = there’s extra of this substance
*the substance won’t run out
*don’t include this reagent in the calculation
If you have 20 loaves of bread, 1 jar of peanut butter and 1 jar of jelly – which ingredient is in excess?

30. Limiting Reagent
To determine the limiting reagent, more than one problem must be done
Ex: You have 8 slices of bread and 9 T of peanut butter. Which is the limiting ingredient? (2Br + 3Pb + 2Je  1 Sa)
8 Br x 1Sa = 4 Sa 9 Pb x 1Sa = 3 Sa
2 Br Pb

31. Limiting Reagent
The reactant that produces the smallest amount of product is the limiting reagent.
8 Br x 1Sa = 4 Sa 9 Pb x 1Sa = 3 Sa
2 Br Pb
Limiting reagent
Smaller quantity

32. Uses for Limiting Reactants
Nutritional value of food for body
Concentration of pollutants

33. What to do (write these down):
Balance equation
Convert: 1-have to moles
2-need to moles
Compare  have : need
One must be > or <
ID the LR
Excess  compare your have : need

35. Cu + AgNO3  Cu(NO3)2 + Ag Balance first
Know: you have 3.5 grams of Cu and 6 grams of AgNO3. What is the LR and what is excess?

36. Cu + AgNO3  Cu(NO3)2 + Ag
3.5 grams of Cu / 6 grams of AgNO3

37. Al + O2  Al2O3
Balance
Known: mole of powdered Al is placed in a container with moles of oxygen. What is the limiting reactant?

38. Al + O2  Al2O3
0.048 mole Al / moles of oxygen

39. Stoichiometry Ratios and Proportions Mole Ratios Limiting Reagent
Yield
Gas Stoichiometry

41. % Yield Theoretical Yield = calculated mass of product
Actual Yield = mass of product found in lab
Percent Yield = actual yield x 100%
theoretical yield

42. Percent Yield
Methanol can be produced through the reaction of CO and H2 in the presence of a catalyst.
CO(g) + 2H2(g)  CH3OH(l)
If 75.0 g of CO reacts to produce 68.4 g CH3OH, what is the percent yield of CH3OH?
79.8%

43. % Yield
Chlorobenzene, C6H5Cl is used in the production of many important chemicals, such as aspirin, dyes, and disinfectants.
C6H6(l) + Cl2(g)  C6H5Cl(s) + HCl(g)
When 36.8 g of C6H6 react with an excess of Cl2, the actual yield of C6H5Cl is 38.8 g. What is the percent yield of C6H5Cl?
73.2%

44. % Yield
Aluminum reacts with excess copper (II) sulfate according to the reaction below. If 1.85 g of Al react and the percent yield of Cu is 56.6%, what mass of Cu is produced?
Al(s) + CuSO4(aq)  Al2(SO4)3(aq) + Cu(s)
3.70 g

45. Stoichiometry Ratios and Proportions Mole Ratios Limiting Reagent
Yield
Gas Stoichiometry

46. *This volume assumes standard temperature and pressure conditions
Molar Volume
Molar volume = the space that one mole of ANY gas fills
1 mole = *22.4 liters
Remember: 1 L = 1000 mL
*This volume assumes standard temperature and pressure conditions

47. Molar Volume
1) A quantity of gas has a volume of cm3.  How many moles of gas are there?

48. Molar Volume 2) Hydrogen sulfide occupies 278.2cm3.
What is the mass of the hydrogen sulfide?

49. Gas Stoichiometry
Instead of counting moles in a reaction, we can also count liters of a gas.
1 liter of N2 reacts with 3 liters of H2 to produce 2 liters of NH3

50. Gas Stoichiometry
What volume of water vapor will be formed when 8.2 L of H2 reacts with excess O2?
2H2 (g) + O2 (g)  2H2O(g)
Use a liter-liter ratio!

51. Gas Stoichiometry
What volume of ammonia will form when 52.5 g of nitrogen reacts with excess hydrogen?
gN2  mol N2  mol NH3  L NH3
gN2  mol N2  L N2  L NH3

52. Keep digging! No pun intended