Stoichiometry Notes

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Real Life Application

Ingredients

2 1/4 cups all-purpose flour

1 teaspoon baking soda

1 teaspoon salt

1 cup (2 sticks) butter, softened

3/4 cup granulated sugar

3/4 cup packed brown sugar

1 teaspoon vanilla extract

2 large eggs

2 cups (12-oz. pkg.) NESTLÉ® TOLL HOUSE® Semi-Sweet Chocolate Morsels

1 cup chopped nuts

Real Life Application

We cannot forget about the law of conservation of mass.

The mass of what we put in must be equal to what we get out.

KC 1: The excess reactants are all the leftover unused reactants. (The reactant that’s leftover).

Particle and Mole Relationships

Chemical reactions stop when one of the reactants is used up

KC 2: Stoichiometry is the study of quantitative relationships between the amounts of reactants used and amounts of products formed by a chemical reaction

So based on how much reactant you put in you can calculate how much product you will get out

Particle and Mole Relationships

Particle and Mole Relationships

KC 3: A mole ratio is a ratio between the numbers of moles of any 2 substances in a balanced equation

This can only be determined from a balanced chemical equation

Particle and Mole Relationships

Let practice: What is the mole-to-mole ratio for… 10C2H4O + 15O2 20CO2 + 2H2O

CH4 + 2O2 CO2 + 2H2O

H2 + O2 H2O

Using Stoichiometry

CH4 + 2O2 CO2 + 2H2O

Mol CH4 Mole H2O

Using Stoichiometry

Key Concept 4:

How many moles of SO3 are formed if you start with 5 moles of Sulfur and have excess Oxygen?

____S + ____O2 ____SO3

Using Stoichiometry

4Fe(s) + 3O2(g) 2Fe2O3(s)

12.37g Fe

Mol Fe Mole Fe2O3

?? g Fe2O3

Using Stoichiometry

How many grams of Fe2O3 are formed when 12.37g of iron reacts with excess oxygen using the balanced chemical equation below:

4Fe(s) + 3O2(g) 2Fe2O3(s)

Using Stoichiometry

Key Concept 5:

How many grams of lithium nitrate will be needed to make 250 grams of lithium sulfate, assuming that you have an adequate amount of lead (IV) sulfate to do the reaction?

____Pb(SO4)2 + ____LiNO3 ____Pb(NO3)4 + ____Li2SO4

Using Stoichiometry

Key Concept 6:

How many grams of sodium sulfate will be formed if you start with 200 grams of sodium hydroxide and you have an excess of sulfuric acid?

____NaOH + ____H2SO4 ____H2O + ____Na2SO4

Using Stoichiometry

New Conversion Factor:

1 mol of gas = 22.4L (at STP = standard temperature and pressure)

How many moles of sodium chloride are in 3.87 L?

How many grams of sodium chloride are in 3.87L?

Using Stoichiometry

4Fe(s) + 3O2(g) 2Fe2O3(s)

12.37g Fe

Mol Fe Mole Fe2O3

L Fe2O3

Using Stoichiometry

Key Concept 7:

How many liters of sodium sulfate will be formed if you start with 200 grams of sodium hydroxide and you have an excess of sulfuric acid?

____NaOH + ____H2SO4 ____H2O + ____Na2SO4

Practice

How many grams of water are formed when .25L of propane (C3H8) burns at STP with excess oxygen according to the reaction below:

_____C3H8 + ______O2 → ______CO2 + _______H2O

Practice

How many grams of CaCl2 are formed when 21.3g of Ca(OH)2 reacts with excess HCl?

_____Ca(OH)2 + _____HCl ______CaCl2 + ______H2O

Practice

How many grams of BaCl2 are formed from 6.000 moles of Ba(ClO3)2?

_______Ba(ClO3)2 → _______BaCl2 + _____O2

Practice

Iron(III) oxide, Fe2O3, can be reduced to iron by passing carbon monoxide, CO, over the heated oxide. How many moles of iron can be produced from 1.234 moles of iron (III) oxide and excess carbon monoxide?

______Fe2O3(s) + _____CO(g) _____Fe(s) + _____CO2(g)

Practice

Butyne, C4H6, burns in the presence of oxygen in air to produce carbon dioxide, CO2, and water H2O. How many moles of oxygen will be required to produce 45.99 moles of carbon dioxide?

______C4H6 + ______O2 ______CO2 + ______H2O

Limiting and Excess Reactants

KC 8: If you have 2 givens in your problem, it is a limiting reactant problem

KC 9: The reactant that produces the smallest amount of a product is the limiting reactant. This is the reactant that will be used up first in the reaction.

Example

How many grams of Cu can be formed when 167.4 g of Fe reacts with 399.2 g of CuCl2?

2 Fe + 3 CuCl2 3 Cu + 2FeCl3

Steps for solving LR problems

KC 10:

1. Write down the givens

2. Use molar mass to convert to moles

3. Use mole ratio from the balanced equation

4. Convert to desired unit

5. The correct answer is the smallest answer as the reaction will stop once one reactant is gone

Limiting and Excess Reactant

KC 11: 80.0g Cu reacts with 25.0g S. Determine which is the limiting reactant and calculate how much Cu2S is formed in grams?

2Cu(s) + S(s) → Cu2S(s)

Limiting and Excess Reactant

KC 12: What is the limiting reactant if 65g of each reactant is present?

___Zn + ___HCl → ___ZnCl2 + ___H2

Excess and Percent Yield

KC 13: To find how much excess you have you must take the limiting reactant and solve for the excess reactant. You need to look at what you are given versus what you need.

Excess Reactant - Example

How many grams of Cu can be formed when 167.4 g of Fe reacts with 399.2 g of CuCl2?

2 Fe + 3 CuCl2 3 Cu + 2FeCl3

CuCl2 – limiting reactant

188.5g Cu is formed

How many grams of excess is left over?

Percent Yield

KC 14: % yield = actual yield x 100

theoretical yield

KC 15: Actual yield must be found experimentally. It is recognized by words like “produced” and “formed”

KC 16: Theoretical yield is done using stoichiometry. It is a prediction and will always be done using math.

Percent Yield

KC 17: A student calculated she should obtain 28g of a substance. In the experiment, 25g was produced. What is the percent yield of the experiment?

Percent Yield - Example

167.4 g of Fe reacts with 399.2 g of CuCl2 to form 170.3g of copper. What is the percent yield of copper?

2 Fe + 3 CuCl2 3 Cu + 2FeCl3

Practice

KC 18: 11.2g of nickel (II) sulfide reacts with 5.43g of oxygen producing 4.97g of nickel (II) oxide. What is the percent yield of this reaction?

_____NiS2 + _____O2 → _____NiO + _____SO2

Practice

KC 19: You are given 0.45g of Al(OH)3 and 0.55g of H2SO4. The reaction produces 0.15g of water. What is the percent yield of this reaction?

____Al(OH)3 + _____H2SO4 → _____Al2(SO4)3 + _____H2O

Practice

KC 20: You are given 3 moles of lithium and 3 moles of nitrogen. The reaction produces .5 moles of lithium nitride. What is the percent yield of this reaction?

____Li + _____N2 → _____Li3N