Chapter 4: Chemical Reactions and Chemical Quantities

Balancing Chemical Equations

Balancing chemical equations ensures the law of conservation of mass is obeyed, meaning the number of atoms of each element is the same on both sides of the equation.

• Balanced Equation: Each side of the equation has the same number of atoms for every element.

• Steps:

  1. Write the unbalanced equation.

  2. Count atoms of each element on both sides.

  3. Add coefficients to balance atoms (never change subscripts).

  4. Check your work.

• Example:

Stoichiometric Calculations

Stoichiometry involves quantitative relationships between reactants and products in a chemical reaction.

• Mole-to-Mole Conversions: Use coefficients from the balanced equation to convert between moles of reactants and products.

• Grams-to-Moles-to-Grams Conversions: Use molar mass to convert grams to moles, then use stoichiometry to find moles of another substance, and convert back to grams if needed.

• 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 the limiting reactant.

• Actual Yield: The amount of product actually obtained from a reaction.

• Percent Yield:

• Example: If 10.0 g of A reacts with excess B to produce 8.0 g of C, and the theoretical yield is 9.0 g, then

Chapter 5: Introduction to Solutions and Aqueous Solutions

Basic Terminology

Solutions are homogeneous mixtures of two or more substances. The solvent is the substance present in the greatest amount, and the solute is dissolved in the solvent.

• Aqueous Solution: A solution in which water is the solvent.

• Electrolytes: Substances that dissociate into ions in water and conduct electricity (e.g., NaCl).

• Non-electrolytes: Substances that do not form ions in solution (e.g., sugar).

Concentration and Molarity

Concentration describes the amount of solute in a given quantity of solvent or solution.

• Molarity (M):

• Dilution Equation: (where is molarity and is volume)

• Example: To prepare 250 mL of 0.10 M NaCl from a 1.0 M stock solution: , so L = 25 mL.

Aqueous Solutions and Solubility

Solubility rules determine whether an ionic compound will dissolve in water. Dissociation refers to the separation of an ionic compound into its constituent ions in solution.

• Dissociation Example:

• Moles of Ions: Calculate by multiplying the number of formula units by the number of each ion per unit.

Precipitation Reactions

Precipitation reactions occur when two aqueous solutions combine to form an insoluble product (precipitate).

• Predicting Precipitates: Use solubility rules to determine if a solid forms.

• Balancing and Completing Reactions: Write balanced molecular, total ionic, and net ionic equations.

• Stoichiometry: Use balanced equations to calculate amounts of reactants and products.

• Example: Mixing and forms precipitate:

Writing Equations: Molecular, Total Ionic, and Net Ionic

Different forms of equations provide varying levels of detail about the species involved in a reaction.

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

• Total Ionic Equation: Shows all strong electrolytes as ions.

• Net Ionic Equation: Shows only the species that actually change during the reaction; omits spectator ions.

• Spectator Ions: Ions that do not participate in the actual chemical change.

• Example:

  • Molecular:

  • Total Ionic:

  • Net Ionic:

Acid-Base (Neutralization) Reactions

Acid-base reactions involve the transfer of protons (H+) from acids to bases, producing water and a salt.

• Predicting Products: Acid + Base → Salt + Water

• Writing Equations: Use molecular, total ionic, and net ionic forms.

• Stoichiometry: Calculate amounts of acid and base needed for neutralization.

• Titrations: Analytical technique to determine concentration of an acid or base using a solution of known concentration.

• Example:

Oxidation-Reduction (Redox) Reactions

Redox reactions involve the transfer of electrons between species. "LEO says GER" is a mnemonic: Lose Electrons = Oxidation; Gain Electrons = Reduction.

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

• Determining Oxidation Numbers: Use rules (e.g., elements = 0, oxygen = -2, hydrogen = +1, etc.).

• Identifying Oxidized and Reduced Species: The species whose oxidation number increases is oxidized; the one whose oxidation number decreases is reduced.

• Example: In , Zn is oxidized, Cu2+ is reduced.

Types of Chemical Reactions

Chemical reactions can be classified by their patterns:

• Precipitation: Formation of an insoluble product.

• Neutralization: Acid-base reaction producing water and a salt.

• Redox: Electron transfer reactions.

• Combination (Synthesis): Two or more substances combine to form one product.

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

• Single Displacement: One element replaces another in a compound.

• Combustion: Substance reacts with oxygen, producing heat and light (often forms CO2 and H2O).

Appendix: Solubility Table (Purpose and Use)

A solubility table helps predict whether an ionic compound will dissolve in water or form a precipitate. It is essential for determining the products of precipitation reactions.

Additional info: Table entries are a standard summary of common solubility rules for general chemistry.