Chapter 3: Chemical Reactions and Stoichiometry

3.1 Law of Conservation of Mass and Chemical Equations

The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. Chemical equations represent the reactants and products involved, ensuring that the number of atoms of each element is conserved.

• Law of Conservation of Mass: In any chemical reaction, the total mass of reactants equals the total mass of products.

• Balancing Chemical Equations: Adjust coefficients to ensure equal numbers of each atom on both sides of the equation.

• Example:

3.2 Types of Chemical Reactions

Chemical reactions can be classified into several types based on the changes that occur. Understanding these types helps predict products and reaction behavior.

• Combination (Synthesis) Reactions: Two or more substances combine to form a single product. Example:

• Decomposition Reactions: A single compound breaks down into two or more simpler substances. Example:

• Combustion Reactions: A substance reacts with oxygen, releasing energy and forming products such as and . Example:

3.3 Chemical Formulas and Molar Mass

Chemical formulas represent the composition of compounds. Molar mass is the mass of one mole of a substance, calculated from its chemical formula.

• Empirical Formula: The simplest whole-number ratio of atoms in a compound.

• Molecular Formula: The actual number of atoms of each element in a molecule.

• Molar Mass (): The mass of one mole of a substance, in grams per mole (). Formula: , where is the number of atoms and is the atomic mass.

• Example: For ,

3.4 Interconversion of Mass, Moles, and Particles

Stoichiometry involves converting between mass, moles, and number of particles using Avogadro's number and molar mass.

• Avogadro's Number: particles per mole.

• Conversions:

  • Mass to moles:

  • Moles to particles:

• Example: Calculate moles in 36g of water: moles

3.5 Empirical and Molecular Formulas from Composition

Empirical and molecular formulas can be determined from mass percentages of elements in a compound.

• Empirical Formula Calculation: Convert mass percentages to moles, then find the simplest ratio.

• Molecular Formula Calculation: Divide the compound's molar mass by the empirical formula mass to find the multiple.

• Example: A compound with 40% C, 6.7% H, and 53.3% O by mass.

3.6 Stoichiometry of Chemical Reactions

Stoichiometry allows calculation of quantities of reactants and products in chemical reactions.

• Limiting Reactant: The reactant that is completely consumed first, limiting the amount of product formed.

• Theoretical Yield: The maximum amount of product that can be formed from given reactants.

• Percent Yield:

• Example: If 10g of product is obtained but the theoretical yield is 12g, percent yield is

Chapter 4: Solution Chemistry and Aqueous Reactions

4.1 Electrolytes and Dissolution

Electrolytes are substances that dissolve in water to produce ions, enabling the solution to conduct electricity. They are classified as strong, weak, or nonelectrolytes.

• Strong Electrolytes: Completely dissociate into ions in water (e.g., NaCl).

• Weak Electrolytes: Partially dissociate (e.g., acetic acid).

• Nonelectrolytes: Do not produce ions (e.g., sugar).

• Ionic Dissolution: Ionic compounds dissolve by separating into their constituent ions.

4.2 Chemical Equations in Solution

Chemical reactions in aqueous solutions are represented by molecular, ionic, and net ionic equations. Metathesis (double displacement) reactions are common.

• Molecular Equation: Shows all reactants and products as compounds.

• Ionic Equation: Shows all strong electrolytes as ions.

• Net Ionic Equation: Shows only the species that change during the reaction.

• Example: Net ionic:

4.3 Acids, Bases, and Their Properties

Acids and bases are classified by their ability to donate or accept protons. Their strength depends on the degree of ionization in water.

• Acids: Substances that donate protons ().

• Bases: Substances that accept protons or donate ions.

• Strong vs. Weak Acids/Bases: Strong acids/bases ionize completely; weak ones only partially.

• Neutralization Reaction: Acid reacts with base to form water and a salt. Example:

4.4 Oxidation-Reduction (Redox) Reactions

Redox reactions involve the transfer of electrons between species. Oxidation is the loss of electrons; reduction is the gain of electrons.

• Oxidation Number: A value assigned to an atom to indicate its degree of oxidation.

• Identifying Redox Reactions: Track changes in oxidation numbers to determine which species are oxidized or reduced.

• Displacement Reactions: A metal replaces another in a compound based on activity series.

• Example:

4.5 Solution Concentration and Dilution

Concentration expresses the amount of solute in a given amount of solvent. Molarity is the most common unit.

• Molarity ():

• Interconversion: Use molarity to convert between moles and volume.

• Dilution: (where is molarity and is volume)

• Example: To prepare 0.5 L of 0.1 M solution from 1.0 M stock: L

4.6 Stoichiometry in Aqueous Solutions

Stoichiometry in solution involves calculating quantities of reactants and products using molarity and volume.

• Stoichiometric Calculations: Use balanced equations and molarity to determine the amounts of substances involved.

• Example: How many moles of are needed to react with 0.1 mol ?

Table: Types of Electrolytes

Table: Types of Chemical Reactions

Additional info: Some explanations and examples have been expanded for clarity and completeness.