CHAPTER 11: STOICHIOMETRY - Livingston



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|Chapter 12 |

|Stoichiometry Notes Packet |

|Big Picture Ideas: |

|The identity of the reactants helps scientists to predict the products in a chemical reaction. |

|Quantitative relationships exist with all chemical reactions that allow scientists to predict amounts of products formed, reactants consumed, and |

|percent yield based on theoretical maximum. |

|Big Picture Questions: |

|How can quantitative relations in chemical reactions be translated to real-life industry situations? |

|How can you predict the products in a chemical reaction?o |

|Suggested Resources… |Formative Assessments |

|Homework Assignments |Classwork Assignments |

|Laboratory Activities |Textbook pages: Chapter 12 |

Key Terms:

1. stoichiometry

2. mole-mole problems

3. mass-mass problems

4. mass-volume problems

5. volume-volume problems

|Directions: Use this information as a general reference tool to guide you through this unit |

|By the conclusion of this unit, you should know the following: |

|Quantitative relationships exist in all chemical reactions. |

|The amount of reactants directly influences (limits) the amount of product formed. |

|Thermochemical equations show energy changes that accompany chemical reactions. |

|By the conclusion of this unit, you should be able to do the following: |

|Use quantitative relationships to predict amounts of products formed. |

|Define stoichiometry and describe its importance |

|Relate stoichiometry to balanced chemical equations |

|Identify and solve different types of stoichiometry problems |

|Calculate the amount of product formed in a chemical reaction when reactants are present in nonstoichiometric proportions |

|Be able to identify and write balanced chemical equations to solve stoichiometry problems |

|Calculate percent yield |

|Use the mass of a reactant to determine how much heat will be gained or lost. |

6. particle –particle problems

7. expected yield

8. actual yield

9. percent yield

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Review/practice conversions: Use dimensional analysis to make the mole conversions below. Show all work. Label everything!!!!!

1. First, determine the molar mass of each substance below:

|SUBSTANCE |MOLAR MASS |

|AlCl3 | |

| |26.98 + (3 x 35.45) = 133.33 g |

|Cl2 | |

| |35.45 x 2 = 70.9 g |

|Ca3(PO4)2 | |

| |(40.08 x 3) + ( 30.97 x 2) + (16.00 x 8) = 310.18 g |

1. 10.7g of aluminum chloride to formula units

10.7g AlCl3 x 1 mol AlCl3 x 6.02 x 1023 formula units AlCl3

133.33 g AlCl3 1 mol AlCl3

2. 20.0g of chlorine gas to L at STP

20.0g Cl2 x 1 mol Cl2 x 22.4 L Cl2

70.9 g Cl2 1 mol Cl2

3. 4.45 x 1022 molecules of ammonia gas (NH3) to L at STP

4.45 x 1022 molecules NH3 x 1 mol NH3 x 22.4 L NH3

6.02 x 1023 Molecules NH3 1 mol NH3

I. MOLE to MOLE problems

Given the moles of one substance and asked to find the moles of another substance in a RXN

Stoichiometry Step-by-Step!

Ex. How many moles of O2 are needed to react with 0.52 moles of Mg?

Step 1 Balance the equation

2 Mg + O2 ( 2 MgO

Step 2 Write the given mole quantity (start your bridge)

Step 3 Write the mole ratio (moles of what you want / moles of what you have)

▪ This comes from the coefficients in the balanced equation

When nitrogen and hydrogen gas are heated under the correct conditions, ammonia gas (NH3) is formed.

a. Rxn MUST be BALANCED: 1 N2 + 3 H2 ( 2 NH3

b. How many moles of nitrogen react with three moles of hydrogen?

3 mol H2 1 mol N2

3 mol H2

c. How many moles of nitrogen react with six moles of hydrogen?

6 mol H2 1 mol N2

3 mol H2

d. How many moles of ammonia would be formed if 6 moles of hydrogen react with plenty of nitrogen?

6 mol H2 2 mol NH3

3 mol H2

e. How many moles of ammonia would be formed if 2.54 moles of nitrogen react with plenty of hydrogen?

2.54 mol N2 2 mol NH3

1 mol N2

f. How many moles of ammonia could be formed if 3.50 moles of hydrogen react with excess nitrogen?

3.50 mol H2 2 mol NH3

3 mol H2

g. How many moles of nitrogen are needed to react with 6.9 moles of hydrogen?

6.9 mol H2 1 mol N2

3 mol H2

More Practice: Mole Ratio Practice

1. Balance the equation: ____ N2 +__3__H2(_2___NH3

How many moles of hydrogen are needed to completely react with two moles of nitrogen?

2 mol N2 3 mol H2

1 mol N2

2. Balance the equation: __2___KClO3(___2__KCl +___3__O2

How many moles of oxygen are produced by decomposition of six moles of potassium

chlorate?

6 mol KClO3 3 mol O2

2 mol KClO3

3. Balance the equation: _____Zn +___2__HCl(_____ZnCl2 + _____H2

How many moles of hydrogen are produced from the reaction of three moles of zinc with an

excess of hydrochloric acid?

3 mol Zn 1 mol H2

1 mol Zn

4. Balancethe equation: ____C3H8 +__5__O2(__3__CO2 + ___4__H2O

How many moles of oxygen are necessary to react completely with four moles of propane

(C3H8)?

4 mol C3H8 5 mol O2

1 molC3H8

5. Balance the equation: ______K3PO4 +_____Al(NO3)3(__3__KNO3 + ____AlPO4

How many moles of potassium nitrate are produced when two moles of potassium phosphate react with two moles of aluminum nitrate?

2 mol K3PO4 3mol KNO3

1 mol K3PO4

II. MASS to MASS problems: Given the mass of one substance and asked to find the mass of another substance in a RXN

1. Given the balanced equation: 2 KClO3 ( 2 KCl + 3O2

How many grams of potassium chloride are produced if 25.0 g of potassium chlorate decompose?

25 mol KClO3 1 molKClO3 2 molKCl 74.55 g KCl

122.55 g KClO3 2 molKClO3 1 molKCl

III. VOLUME to VOLUME problems: Given the volume of one substance (gas at STP) and asked to find the volume of another substance (gas) in a RXN

1. Given the balanced equation: N2 + 3H2 ( 2NH3

a. At constant temperature and pressure, what volume of hydrogen is necessary to react with five liters of nitrogen to produce ammonia?

5 L N2 1 mol N2 3 mol H2 22.4 L H2

22.4 L N2 1 mol N2

IV. MASS to VOLUME problems: Converting from mass of one substance to volume of another in a RXN

1. Given the balanced equation: C3H8 + 5O2 ( 3CO2 + 4H2O

If 20 grams of oxygen are consumed in the above reaction, how many liters of carbon dioxide are produced?

20 g O2 x 1 mol x 3 mol CO2 x 22.4 L CO2

32 g O2 5 mol O2 1 mol CO2

MIXED PRACTICE

1. When iron is heated in pure oxygen, iron (III) oxide is formed. Write a balanced equation for the reaction below. What type of reaction is it? __synthesis___________

_______4Fe + 3 O2 2 Fe2O3________________________

a. What mass of iron must react with excess oxygen in order to form 4.81 moles of iron(III) oxide?

4.81 mol Fe2O3 4 mol Fe 55.8 g Fe

2 mol Fe2O3 1 mol Fe

b. What mass of iron is needed to react with 40.0 g of oxygen?

40.0 g O2 1 mol O2 4 mol Fe 55.8 g Fe

32.0 g O2 3 mol O2 1 mol Fe

c. What mass of iron(III) oxide can be formed from the reaction of 10.2 g of iron with excess oxygen?

10.2 g Fe1 mol Fe2 mol Fe2O3 159.6 g Fe2O3

55.85 g Fe4 mol Fe 1 mol Fe2O3

d. What mass of oxygen is needed to react with 12.7 g of iron?

12.7 g Fe 1 mol Fe 3 mol O2 32.0 g O2

55.85 g Fe 4 mol Fe 1 mol O2

e. Whatmass of iron(III) oxide will be formed if 10.0 L of oxygen at STP react with excess iron?

10 L O2 1 mol O2 2 mol Fe2O3 159.68 g Fe2O3

22.4 L O2 3 mol O2 1 mol Fe2O3

2. Barium hydroxide reacts with hydrochloric acid to form barium chloride and water. Write a balanced equation for the reaction below. What type is it? _double displacement___

_________Ba(OH)2 + 2HCl (BaCl2+ 2H2O___________________________

a. Whatmass of barium chloride will form if 14.0 g of barium hydroxide reacts with excess hydrochloric acid?

14.0 g Ba(OH)2 1 molBa(OH)2 1 mol BaCl2 208.3 g BaCl2

171.3Ba(OH)2 1 molBa(OH)2 1 molBaCl2

b. How many grams of hydrochloric acid are needed to react with 15.0 g of barium hydroxide?

15.0 gBa(OH)2 1 molBa(OH)2 2 molHCl 36.5 g HCl

171.3Ba(OH)2 1 molBa(OH)2 1 molHCl

c. Whatmass of barium chloride will form if 5.98 g of hydrochloric acid react with excess barium hydroxide?

5.98 g HCl 1molHCl 1 mol BaCl2 208.3 g BaCl2

36.5 g HCl 2 molHCl 1 molBaCl2

d. How many molecules of water are formed by the reaction of 10.8 g of barium hydroxide with excess hydrochloric acid?

10.8 gBa(OH)2 1 molBa(OH)2 2 mol H2O 6.02 x 1023molc. H2O

171.3 g Ba(OH)2 1 molBa(OH)2 1 mol H2O

LIMITING REACTANTS

LIMITING REACTANT: Present in the smallest stoichiometric amount;

Gets used up in the reaction(in this case, the H2);

determines the amount of product

EXCESS REACTANT: Not used up (left over);

added to ensure that the other reactant is completely used up; cheaper & easier to recycle

1. Balance the reaction below:

_4__Al + _3__O2 ( _2__Al2O3

2. 4.0 moles of aluminum are placed in a container with 4.0 moles of oxygen. How many moles of aluminum oxide should form?

There is enough aluminum to make _____________ moles of aluminum oxide.

4 mol Al x 2 mol Al2O3 = 2 mol Al2O3

4 mol Al

There is enough oxygen to make ________________ moles of aluminum oxide.

4 mol O2 x 2 mol Al2O3 = 2.67 mol Al2O3

3 mol O2

______2____________ moles of aluminum oxide will form.

The limiting reactant is __aluminum______. The excess reactant is ____oxygen________.

3. Predict the mass of aluminum oxide that will form if 20.0 g of aluminum react with 15.0 L of oxygen gas at STP.

There is enough aluminum to make ________________ g of aluminum oxide.

20 g Al x 1 mol Al x 2 mol Al2O3 x 102 g Al2O3 = 37.8 g Al2O3

27.0 g Al 4 mol Al 1 mol Al2O3

There is enough oxygen to make ________________ g of aluminum oxide

15 L O2 x 1 mol O2 x 2 mol Al2O3 x 102 g Al2O3 = 45.5 g Al2O3

22.4 L O2 3 mol O2 1 mol Al2O3

_______37.8________ g of aluminum oxide will form.

The limiting reactant is __aluminum______. The excess reactant is ____oxygen________.

1. Fluorine gas is bubbled through a solution of potassium iodide. The products of the reaction are potassium fluoride and iodine. Write a balanced equation for the reaction below.

F2 + 2 KI ( 2 KF + I2

What type of reaction is this? _single replacement___

12.6 g of fluorine is bubbled through a solution containing 20.15 g of potassium iodide. What mass of potassium fluoride should form?

12.6 g F2 x 1 mol F2 x 1 mol KF x 58.1 g KF = 9.63 g KF

38.0 g F2 2 mol F2 1 mol KF

20.15 g KI x 1 mol KI x 1 mol KF x 58.1 g KF = 7.05 g KF

166.0 g KI 1 mol KI 1 mol KF

Mass of KF that will form is 7.05

The limiting reactant is __potassium iodide__. The excess reactant is ___fluorine______.

SAMPLE PROBLEM: FINDING THE MASS OF EXCESS REACTANT

What mass of copper(II) iodide will be formed if 35.0g of copper are placed in a solution containing 90.0g of silver iodide?

a. Balanced Reaction: ___ Cu + 2 AgI ( CuI2 + 2 Ag __________________

b. Find the expected yield if copper is the limiting reactant:

35.0g Cu 1 mol Cu 1 mol CuI2 317.3g CuI2 = 174.9g CuI2

63.5g 1 mol Cu 1 mol CuI2

c. Find the expected yield if silver iodide is the limiting reactant:

90.0g AgI 1 mol AgI 1 mol CuI2 317.3g CuI2 = 60.8g CuI2

234.8g 2 mol AgI 1 mol CuI2

d. The limiting reactant is ____AgI____________. The excess reactant is ____Cu______.

e. Use the limiting reactant to determine how much of the excess reactant does react.

90.0g AgI 1 mol AgI 1 mol Cu 63.5g = 12.2g Cu reacted

234.8g 2 mol AgI 1mol CuI2

f. Subtract the amount that reacts from the amount you started with to find the mass remaining.

35.0g Cu– 12.2g Cu = 22.8g Cu remain

FINDING THE MASS OF EXCESS REACTANT

The next step in the limiting reactant process is determining the amount of excess reactant remaining following the reaction. There is a sample problem on the previous page. Follow the steps of the sample problem if you get lost!

Try the problem below:

1. What mass of carbon dioxide will be formed if 50.0g of propane gas are burned in 40L of pure oxygen at STP?

a. Balanced reaction: _C3H8 + 5 O2 ( 3 CO2 + 4 H2O____________________

b. Find the expected yield of carbon dioxide if propane is the limiting reactant:

50 g C3H8 x 1 mol C3H8 x 3 mol CO2 x 44.01 g CO2 = 149.73 g CO2

44.09 g C3H8 1 mol C3H8 1 mol CO2

c. Find the expected yield of carbon dioxide if oxygen is the limiting reactant:

40 L O2 x 1 mol O2 x 3 mol CO2 x 44.01 g CO2 = 47.15 g CO2

22.4 L O2 5 mol O2 1 mol CO2

d. The limiting reactant is ___O2_______. The excess reactant is ______C3H8_________.

e. Use the limiting reactant to determine how much of the excess reactant does react.

40 L O2 x 1 mol O2 x 1 mol C3H8 x 44.09 g C3H8 = 15.75 g C3H8

22.4 L O2 5 mol O2 1 mol C3H8

f. Subtract the amount that reacts from the amount you started with to find the mass of propane gas remaining.

50 – 15.75 = 34.25 g C3H8 remains

Percent Yield (How well did you do in the lab?)

• If you calculated a 3% error in a lab, then you should have a 97% yield.

• If you calculated a 10% error in a lab, then you should have a 90% yield.

Percent Yield: a comparison of how much product you produced in the lab and what you theoretically should have made according to your calculations.

1. A student burns 20.0L of propane gas in excess oxygen at STP. Determine the volume of carbon dioxide that should form in the reaction.

__1__C3H8 + __5__O2 ( __3__CO2 + __4__H2O

The reaction only produces 48.0 L of carbon dioxide. What is the percent yield?

20 L C3H8 x 1 mol C3H8 x 3 mol CO2 x 22.4 L CO2 = 60.0 L CO2

22.4 L C3H8 1 mol C3H8 1 mol CO2

What is the percent error? (100 – 80) = 20%

2. Sodium chlorate decomposes to produce sodium chloride and oxygen. Write and balance the reaction. The determine the mass of sodium chloride should form if 150g of sodium chlorate decomposes?

Reaction: 2 NaClO3 ( 2 NaCl + 3 O2

150 g NaClO3 x 1 mol NaClO3 x 2 mol NaCl x 58.5 g NaCl = 82.4 g NaCl

106.5 g NaClO3 2 mol NaClO3 1 mol NaCl

The reaction above is carried out in the lab, and 55 g of sodium chloride is collected.

What is the percent yield?

(55 ÷ 82.4) x 100% = 66.7%

Determine the percent error.

(100 – 66.7) = 33.3%

EXTRA NOTES

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1 mole = 6.02 x 1023 molecules (covalent)

1 mole = 6.02 x 1023 formula units (ionic) HOW MANY PARTICLES

1 mole = 6.02 x 1023 atoms (monoatomic element)

1 mole = molar mass (grams) - HOW HEAVY

1 mole = 22.4L for a gas at STP – HOW MUCH SPACE

4.83 x1022formula units

6.32 L

1.66 L

Stoichiometry: mass relationships between substances in a chemical reaction

based on the mole ratio; Comparing chemical quantities to convert one element or compound to another.

Stoichiometric quantities - chemicals are usually mixed in exact amounts so that all the reactants will run out

Ex. H2 reacts with N2 to produce NH3.

If 33 L of H2 react, how many grams of NH3 do we produce?

Liter of H2 ( moles of H2 ( moles of NH3 ( grams of of NH3

2 mol N2

4 mol NH3

5.08 mol NH3

2.33 mol NH3

2.3 mol N2

6 mol H2

9 mol O2

3 mol H2

20.0 mol O2

6 mol KNO3

15.21 g KCl

15 L N2

8.4 L CO2

536.80 g Fe

93.07 g O2

14.58 gFe2O3

5.46 g O2

47.52 g Fe2O3

17.02 g BaCl2

6.39 g HCl

17.06 g BaCl2

7.59 x 1022molc. H2O

What you actually produced in lab

What stoichiometry predicts you will produce. (from calculation-theoretically)

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