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Stoichiometry and Reactions in Aqueous Solution: Study Notes for General Chemistry

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Stoichiometry: Chemical Reactions and Reaction Stoichiometry

Introduction to Stoichiometry

Stoichiometry is the quantitative study of the relationships between the amounts of reactants and products in chemical reactions. It is based on the Law of Conservation of Mass, which states that mass is neither created nor destroyed in a chemical reaction.

  • Chemical equations represent reactions, with reactants on the left and products on the right, separated by an arrow.

  • Coefficients are used to balance equations, ensuring the number of atoms for each element is equal on both sides.

  • Subscripts in chemical formulas should not be changed when balancing equations; only coefficients are adjusted.

Types of Chemical Reactions

Chemical reactions can be classified into several types, including combination, decomposition, and combustion reactions.

  • Combination reactions: Two or more substances react to form one product.

  • Decomposition reactions: One substance breaks down into two or more substances.

  • Combustion reactions: Rapid reactions that produce a flame, often involving oxygen as a reactant.

Table of combination and decomposition reactions

Balancing Chemical Equations

A chemical equation is balanced when the number of atoms of each element is the same on both sides. Coefficients are used to achieve this balance.

  • Example:

  • Changing subscripts alters the identity of the compound, which is not allowed.

Formula Weight and Molecular Weight

  • Formula weight is the sum of atomic weights for the atoms in a chemical formula (expressed in amu).

  • Molecular weight is the sum of atomic weights for the atoms in a molecule.

  • For ionic compounds, use the empirical formula to calculate formula weight.

Percent Composition

The percentage of mass contributed by each element in a compound can be calculated using:

Avogadro’s Number and the Mole Concept

  • One mole contains particles (atoms, molecules, or ions).

  • Molar mass is the mass of 1 mole of a substance (g/mol).

  • The formula weight (in amu) is numerically equal to the molar mass (in g/mol).

Conversion between grams, moles, and formula units using Avogadro's number

Stoichiometric Calculations

Stoichiometric calculations involve converting between mass, moles, and number of particles using balanced equations and molar relationships.

  • Use mole ratios from balanced equations to relate quantities of reactants and products.

  • Example: Calculating grams of water produced from 1.00 g of glucose:

Stoichiometric calculation steps Example stoichiometric calculation for water produced from glucose

Limiting Reactant, Theoretical Yield, and Percent Yield

  • Limiting reactant: The reactant present in the smallest stoichiometric amount, which limits the amount of product formed.

  • Theoretical yield: The maximum amount of product that can be formed from the limiting reactant.

  • Actual yield: The amount of product actually obtained from the reaction.

  • Percent yield:

Reactions in Aqueous Solution

Properties of Solutions

  • Solution: Homogeneous mixture of two or more pure substances.

  • Solvent: Substance present in greatest abundance.

  • Solute: All other substances in the solution.

  • Aqueous solution: Solution where water is the solvent.

Electrolytes and Nonelectrolytes

  • Electrolyte: Substance that dissociates into ions when dissolved in water.

  • Nonelectrolyte: Substance that does not dissociate into ions in water.

  • Strong electrolyte: Dissociates completely in water.

  • Weak electrolyte: Dissociates partially in water.

Table summarizing electrolytic behavior of compounds

Solubility of Ionic Compounds

Not all ionic compounds dissolve in water. Solubility rules help predict which compounds are soluble. Solubility guidelines for common ionic compounds in water

Precipitation Reactions

  • Occur when two solutions containing soluble salts are mixed and an insoluble salt (precipitate) forms.

  • Metathesis (double displacement) reactions involve exchange of ions between reactants.

Acids and Bases

  • Acids: Substances that ionize in aqueous solution to form H+ ions (proton donors).

  • Bases: Substances that accept H+ ions or increase OH– concentration in water.

  • Strong acids and bases dissociate completely; weak acids and bases dissociate partially.

Molecular representation of acid-base reaction between water and ammonia Table of common strong acids and bases Molecular models of acids

Neutralization Reactions

  • Reactions between an acid and a base produce water and a salt.

  • Can be written as molecular, complete ionic, or net ionic equations.

Neutralization reaction equation

Redox and Displacement Reactions

  • Oxidation: Loss of electrons.

  • Reduction: Gain of electrons.

  • Redox reactions involve transfer of electrons; displacement reactions involve replacement of ions by elements.

Molarity and Solution Concentration

  • Molarity (M):

  • Concentration can be changed by dilution:

  • Titration: Analytical technique to determine concentration of a solute.

Summary Table: Combination and Decomposition Reactions

Type

General Equation

Example

Description

Combination

A + B → C

2K(s) + Cl2(g) → 2KCl(s)

Two or more reactants combine to form a single product.

Decomposition

C → A + B

2KClO3(s) → 2KCl(s) + 3O2(g)

A single reactant breaks apart to form two or more substances.

Summary Table: Common Strong Acids and Bases

Strong Acids

Strong Bases

Hydrochloric acid (HCl) Hydrobromic acid (HBr) Hydroiodic acid (HI) Chloric acid (HClO3) Perchloric acid (HClO4) Nitric acid (HNO3) Sulfuric acid (H2SO4)

Group 1A metal hydroxides (LiOH, NaOH, KOH, RbOH, CsOH) Heavy group 2A metal hydroxides (Ca(OH)2, Sr(OH)2, Ba(OH)2)

Summary Table: Electrolytic Behavior of Compounds

Strong Electrolyte

Weak Electrolyte

Nonelectrolyte

Ionic

All

None

None

Molecular

Strong acids

Weak acids, weak bases

All other compounds

Summary Table: Solubility Guidelines for Ionic Compounds

Soluble Ionic Compounds

Important Exceptions

NO3–, CH3COO–, Cl–, Br–, I–, SO42–

Compounds of Ag+, Hg22+, Pb2+ (for Cl–, Br–, I–); Compounds of Ba2+, Hg22+, Pb2+ (for SO42–)

Insoluble Ionic Compounds

Important Exceptions

S2–, CO32–, PO43–, OH–

Compounds of NH4+, alkali metal cations (for all); Ca2+, Sr2+, Ba2+ (for OH–)

Summary Table: Steps in Stoichiometric Calculations

Step

Description

1

Convert grams of substance A to moles using molar mass.

2

Use coefficients from balanced equation to convert moles of A to moles of B.

3

Convert moles of B to grams using molar mass.

Example: Acid-Base Neutralization

  • Reaction:

  • Acid reacts with base to produce water and salt.

Neutralization reaction equation

Example: Acid-Base Molecular Models

Molecular models of acids

Example: Acid-Base Reaction Mechanism

Molecular representation of acid-base reaction between water and ammonia

Example: Stoichiometric Calculation for Water Produced

Example stoichiometric calculation for water produced from glucose

Example: Conversion Pathways in Stoichiometry

Conversion between grams, moles, and formula units using Avogadro's number

Example: Steps in Stoichiometric Calculations

Stoichiometric calculation steps

Additional info:

  • Tables and images included are directly relevant to the explanation of combination/decomposition reactions, acid-base chemistry, stoichiometric calculations, and solubility rules.

  • All equations are provided in LaTeX format for clarity and academic rigor.

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