General Chemistry I: Core Concepts and Problem-Solving Guide (Chapters 4–7)

Chapter 4: Chemical Reactions and Stoichiometry

Balancing Chemical Equations

Balancing chemical equations ensures the law of conservation of mass is obeyed, with equal numbers of each atom on both sides of the equation.

• Reactants: Substances present before the reaction.

• Products: Substances formed as a result of the reaction.

• Balancing Steps:

  1. Write the unbalanced equation.

  2. Count atoms of each element on both sides.

  3. Add coefficients to balance atoms, starting with the most complex molecule.

  4. Check all elements and adjust as needed.

Stoichiometry: Mass and Yield Calculations

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

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

• Percent Yield: The ratio of actual yield to theoretical yield, expressed as a percentage.

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

Key Formulas:

• Percent Yield: $\text{Percent Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100\%$

• Limiting Reactant: Compare mole ratios from the balanced equation to determine which reactant produces the least product.

Example: If 5.0 g of A reacts with 10.0 g of B to produce C, calculate the limiting reactant and percent yield if 7.0 g of C is obtained.

Chapter 5: Aqueous Reactions and Solution Stoichiometry

Electrolytes and Nonelectrolytes

Electrolytes are substances that dissociate into ions in water, conducting electricity. Nonelectrolytes do not dissociate and do not conduct electricity.

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

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

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

Acids and Bases

Acids donate protons (H+), while bases accept protons. Strong acids/bases dissociate completely; weak acids/bases do not.

• Strong Acids: HCl, HNO3, H2SO4

• Weak Acids: CH3COOH

Solubility and Precipitation Reactions

Solubility rules determine if a compound is soluble in water. Precipitation reactions form insoluble products (precipitates).

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

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

Solution Concentration and Calculations

• Molarity (M): $M = \frac{\text{moles of solute}}{\text{liters of solution}}$

• Solution Dilution: $M_1V_1 = M_2V_2$

Titration and Redox Reactions

• Titration: Technique to determine concentration of an unknown solution using a reaction with a standard solution.

• Oxidation Numbers: Assigned to atoms to track electron transfer in redox reactions.

• Oxidizing Agent: Causes oxidation, is reduced.

• Reducing Agent: Causes reduction, is oxidized.

Example: In the reaction between Fe2+ and MnO4-, identify the oxidizing and reducing agents.

Chapter 6: Gases and the Kinetic Molecular Theory

Gas Laws and Calculations

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

• Ideal Gas Law: $PV = nRT$

• Standard Temperature and Pressure (STP): 0°C (273.15 K) and 1 atm.

• Unit Conversions: 1 atm = 760 mmHg = 101.325 kPa

Partial Pressure and Mole Fraction

• Dalton's Law of Partial Pressures: $P_{\text{total}} = \sum P_i$

• Mole Fraction: $X_i = \frac{n_i}{n_{\text{total}}}$

Kinetic Molecular Theory and Gas Behavior

• Root Mean Square Speed: $u_{\text{rms}} = \sqrt{\frac{3RT}{M}}$

• Rate of Effusion: $\text{Rate} \propto \frac{1}{\sqrt{M}}$

Example: Calculate the rate of effusion of hydrogen gas compared to oxygen gas.

Chapter 7: Thermochemistry

Energy, Work, and Heat

Thermochemistry studies energy changes in chemical reactions, focusing on heat (q), work (w), and internal energy (E).

• Law of Conservation of Energy: Energy cannot be created or destroyed, only transformed.

• System vs. Surroundings: The system is the part of the universe under study; surroundings are everything else.

• Sign Conventions: Heat absorbed by the system is positive; heat released is negative.

Enthalpy and Calorimetry

• Heat Transfer: $q = mc\Delta T$

• Enthalpy Change: $\Delta H = \sum \Delta H_f^\circ(\text{products}) - \sum \Delta H_f^\circ(\text{reactants})$

• Hess's Law: The total enthalpy change is the sum of enthalpy changes for individual steps.

Phase Changes and Energy Calculations

• Calculate heat during phase changes using enthalpy of fusion or vaporization.

• Calculate $\Delta E$ (change in internal energy) using $\Delta E = q + w$.

Example: Calculate the heat required to convert 10 g of ice at 0°C to water at 25°C.

Term	Definition	Example
Strong Electrolyte	Completely dissociates in water	NaCl
Weak Electrolyte	Partially dissociates in water	CH3COOH
Nonelectrolyte	Does not dissociate in water	Sucrose

Additional info: These notes are structured to provide a comprehensive review of key General Chemistry I concepts, including definitions, formulas, and example applications, suitable for exam preparation.