Chapter 4: Chemical Reactions and Stoichiometry

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.

• Why Balance Equations: To reflect that matter is neither created nor destroyed in a chemical reaction.

• How to Balance: Adjust coefficients (whole numbers in front of compounds or elements) to achieve equal numbers of each atom on both sides.

• Example:

Types of Chemical Reactions

Chemical reactions can be classified into several types based on the rearrangement of atoms and ions.

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

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

• Single Displacement: An element replaces another in a compound. Example:

• Double Displacement (Precipitation/Neutralization): Ions in two compounds exchange partners. Example (Precipitation): Example (Neutralization):

• Combustion: A substance reacts with oxygen, releasing energy, usually as heat and light. Example:

Stoichiometry: Moles, Mass, and Limiting Reactant

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

• Conversions: Use molar mass and balanced equations to convert between moles and grams of reactants/products.

• 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.

• Percent Yield:

• Example: If 10.0 g of A reacts with 15.0 g of B to produce 12.0 g of C, and the theoretical yield is 14.0 g, then percent yield is .

Chapter 5: Solutions, Precipitation, and Gas Laws

Solubility and Precipitation Reactions

Solubility rules help predict whether a compound will dissolve in water or form a precipitate.

• Solubility Table: Use to determine if an ionic compound is soluble or insoluble in water.

• Precipitate: An insoluble solid formed when two solutions are mixed.

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

• Writing Equations:

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

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

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

• Example: Mixing and forms precipitate. Molecular: Net Ionic:

Molarity and Solution Calculations

Molarity (M) is a measure of concentration, defined as moles of solute per liter of solution.

• Formula:

• Dilution Equation: (where 1 = initial, 2 = final)

• Stoichiometry: Use molarity and volume to find moles for reactions in solution.

• Example: To prepare 250 mL of 0.5 M NaCl from 2.0 M NaCl: , so L or 62.5 mL.

Electrolytes

Electrolytes are substances that conduct electricity when dissolved in water.

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

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

• Non-Electrolytes: Do not dissociate (e.g., sugar, ethanol).

Gas Laws

Gas laws describe the relationships between pressure, volume, temperature, and amount of gas.

• Ideal Gas Law: Where P = pressure (atm), V = volume (L), n = moles, R = 0.08206 L·atm/(mol·K), T = temperature (K).

• Boyle's Law: (at constant n, T)

• Charles's Law: (at constant n, P)

• Avogadro's Law: (at constant P, T)

• Gay-Lussac's Law: (at constant n, V)

• Combined Gas Law:

• Conversions: 1 atm = 760 mmHg = 101.3 kPa; 1 mL = 1 x 10-3 L

• STP Conditions: 1 atm, 0°C (273.15 K); 1 mol of any gas occupies 22.4 L at STP.

• Density of a Gas: (where M = molar mass)

• Molar Mass from Gas Data:

• Example: Calculate the volume occupied by 2.0 mol of O2 at STP: L.

Summary Table: Gas Laws and Their Relationships

Additional Notes

• A periodic table and solubility rules table will be provided during exams.

• You may use a 5" x 5" notecard with equations and notes for reference.

• Be sure to memorize or note all required equations and conversions.