Chapter 4 Stoichiometry of Chemical Reactions

Chapter 4 Stoichiometry of Chemical Reactions

By Dr. Luis Bello

​Previously

​3.1 Formula Mass and the Mole Concept

3.2 Determining Empirical and Molecular Formulas

3.3 Molarity

3.4 Other Units for Solution Concentrations

​Checking Comprehension

Multiple Choice

What is the molar mass of NaCl?

• 58.45g/mol

• 28g/mol

• 12g/mol

• 6.02 x 10²³

Multiple Choice

Calculate the % composition by mass of oxygen present in H₂SO₄.

• 16.3%

• 65.25%

• 32.6%

• 57.14%

Multiple Choice

How many moles are 98.3 grams of aluminum hydroxide, Al(OH)₃?

• 1.26 moles
• 0.8 moles
• 7,673.4 moles
• 150 moles

Multiple Choice

A compound consists of 72.2% magnesium(Mg) and 27.8% nitrogen(N) by mass. What is the empirical formula?

• Mg₄N₃
• MgN₂
• Mg₃N₂ 
• MgN

Multiple Choice

Which of the following is considered an empirical formula?

• CH₃COOH
• C₆H₁₂O₆
• H₂O

Multiple Choice

What is the molarity of 3 mole of hydrochloric acid in 3 L of water. 

• 3
• 1
• 6
• 9

Multiple Choice

What is the molarity of 4 grams of sodium chloride in 3,800 mL of solution?

• 0.018 M
• 0.018 mol
• 1.052 M
• 1.052 mol

Multiple Choice

50 ml of a 1 M solution is diluted until the final volume is 80ml. How much water was added?

• 50 ml

• 1.3 ml

• 30 ml

• 130 ml

Multiple Choice

What is the molarity of a solution made by diluting 26.5 mL of 6.00M HNO₃ to a volume of 250 mL?

• 15.9 M
• 0.636 M
• 0.642 M
• 1.59 M

Multiple Choice

Which solution is more concentrated?

Solution 1:

500 mL of water

100 g of salt

Solution 2:

500 mL of water

90 g of salt

• Solution 1

• Solution 2

• They have the same concentration

• I have no idea

Multiple Choice

Which solution is more diluted?

Solution 1:

1000 mL of water

60g of salt

Solution 2:

500 mL of water

60 g of salt

• Not enough information to tell

• Solution 1

• Solution 2

• They are equally diluted

​Chapter Outline

4.1 Writing and Balancing Chemical Equations

4.2 Classifying Chemical Reactions

4.3 Reaction Stoichiometry

4.4 Reaction Yields

4.5 Quantitative Chemical Analysis

Multiple Choice

Balance this equation

_Al +_HCl --> _H₂ +_AlCl₃

• 2,6,3,2

• it's already balanced

• 4,12,3,4

• 2,1,4,5

Multiple Choice

Balance this chemical reaction......?  
__H₂O₂ ---->  __H₂O + O₂

• 2H₂O_{2  //}  2H₂O
• 1H₂O_{2  //}  2H₂O
• 2H₂O_{2  //}  1H₂O
• H₂O_{2  //}  2H₂O

Multiple Choice

How many HCl molecules do you need to balance this equation? 
Mg +  __HCl --->  MgCl₂ + H₂

• 1
• 2
• 3
• 4

Open Ended

Balance the following equation and choose the quantity which is the sum of the coefficients of the reactants.

C₈H₈O₂ + ____ O₂ ____ CO₂ + ____ H₂O

​Classifying Chemical Reactions

​

• Define three common types of chemical reactions precipitation,

• acid-base, and

• oxidation-reduction

​A precipitation reaction is one in which dissolved substances react to form one (or more) solid products. Many reactions of this type involve the exchange of ions between ionic compounds in aqueous solution and are sometimes referred to as double displacement, double replacement, or metathesis reactions. These

​Acid-Base Reactions

​

An acid-base reaction is one in which a hydrogen ion, H⁺, is transferred from one chemical species to another.

​Oxidation-reduction (redox) reactions are those in which one or more elements involved undergo a change in oxidation number.

​Balancing Redox Reactions via the Half-Reaction Method

​

1. Write the two half-reactions representing the redox process.

2. Balance all elements except oxygen and hydrogen.

3. Balance oxygen atoms by adding H₂O molecules.

4. Balance hydrogen atoms by adding H⁺ ions.

5. Balance charge by adding electrons.

6. If necessary, multiply each half-reaction’s coefficients by the smallest possible integers to yield equal numbers of electrons in each.

7. Add the balanced half-reactions together and simplify by removing species that appear on both sides of the equation.

​

​

​Balancing Redox Reactions in Acidic Solution

​8. For reactions occurring in basic media (excess hydroxide ions), carry out these additional steps:

1. Add OH⁻ ions to both sides of the equation in numbers equal to the number of H⁺ ions.

2. On the side of the equation containing both H⁺ and OH⁻ ions, combine these ions to yield water molecules.

3. Simplify the equation by removing any redundant water molecules.

​

9. Finally, check to see that both the number of atoms and the total charges¹ are balanced.

​Balancing in a basic media (excess hydroxide ions)

​Reaction Stoichiometry

​

relationships between the amounts of reactants and products of a chemical reaction

​

​Limiting Reactant

​

reactant present in an amount lower than required by the reaction stoichiometry, thus limiting the amount of product generated

​

​Percent Yield

​

​

measure of the efficiency of a reaction, expressed as a percentage of the theoretical yield

​

​Titration

​​Gravimetric Analysis:

​

quantitative chemical analysis method involving the separation of an analyte from a sample by a physical or chemical process and subsequent mass measurements of the analyte, reaction product, and/or sample

Multiple Choice

2 KClO₃ → 2 KCl + 3 O₂
How many moles of oxygen are produced when 6.7 moles of KClO₃ decompose completely?

• 6.7 mol
• 1.0 mol
• 10.1 mol
• 4.5 mol

Multiple Choice

2Na + 2H₂O → 2NaOH+ H₂
How many grams of hydrogen are produced if 120 g of Na are available?

• 5.2 g
• 2.6 g
• 690 g
• 45 g

Multiple Choice

 SiO₂ + 3C → SiC + 2CO
I need to add 8 moles of Carbon to the reaction. How many grams of Carbon should I weigh?

• _{96 g}
• 0.67 g
• 2.67 g
• 48 g

Multiple Choice

Cl₂ + 2 KBr → Br₂ + 2 KCl
How many grams of potassium chloride can be produced from 356 g of chlorine and 356 g of potassium bromide?

• 749 g
• 223 g
• 479 g
• 814 g

Open Ended

Aluminum combines with iodine according to the following equation. How many grams of AlI₃ can be formed when 1.00 g of aluminum reacts with 12.00 g of iodine? (Atomic weights: Al = 26.98, I = 126.9).

2 Al + 3 I₂ --> 2 AlI₃

a)   12.63

b)   13.00

c)   12.44

d)   12.85

e)   12.21

Multiple Choice

How much water can be made if 8 moles of NH₃ react with 6 moles of NO?

4NH₃+6NO --> 5N₂ + 6H₂O

• 5 moles

• 6 moles

• 12 moles

• 18 moles

Multiple Choice

In a lab, a scientist calculated that he should produce 12.3 grams of product in his experiment. When he is finished collecting his product it weighs 10.1 grams. What is his percent yield?

• 82.1%

• 22.8%

• 18.7%

• 12.2%

Multiple Choice

Theoretical yield = 73g

Actual yield = 62g

Calculate the percent yield.

• 18%

• 118%

• 85%

• 15%

Multiple Choice

Calculate the theoretical yield if given the actual yield and percent yield are 51.4g and 77.0% respectively.

• 25.6g

• 1.5g

• 15g

• 66.8g

Open Ended

The reaction of 4.0 mol of H₂ with 2.0 mol of I₂ produces 1.0 mol of HI. Determine the limiting reagent and the percent yield for this reaction. (Atomic weights: H = 1.008; I = 126.9).

H₂ + I₂ ---> 2 HI

a)   I₂, 50%

b)   H₂, 25%

c)   H₂, 50%

d)   I₂, 25%

e)   H₂, 75%