GOB Chemistry Exam 2 Study Guide: Chemical Reactions, Acids & Bases, and Hydrocarbons

Chapter 8: Chemical Reactions and Stoichiometry

Parts and Balancing of Chemical Equations

Chemical equations represent the reactants and products in a chemical reaction. Balancing ensures the law of conservation of mass is obeyed.

• Reactants are substances present before the reaction; products are formed after the reaction.

• Balancing involves adjusting coefficients so the number of atoms of each element is equal on both sides.

• Example: $2H_2 + O_2 \rightarrow 2H_2O$

Types of Chemical Reactions

Chemical reactions can be classified by how reactants are transformed into products.

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

• Decomposition: A single compound breaks down into two or more products.

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

• Double Displacement: Exchange of ions between two compounds.

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

• Example: $CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$ (combustion)

Stoichiometry and Mole Calculations

Stoichiometry involves quantitative relationships in chemical reactions.

• Mole: The amount of substance containing $6.02 \times 10^{23}$ particles (Avogadro's number).

• Molar Mass: The mass of one mole of a substance (g/mol).

• Conversions: Use molar mass to convert between grams and moles.

• Example: To find moles in 18g of water: $\text{moles} = \frac{18\ g}{18.02\ g/mol} = 1\ mol$

Limiting Reactant and Theoretical Yield

The limiting reactant determines the maximum amount of product formed.

• Calculate moles of each reactant; the one producing the least product is limiting.

• Theoretical yield: The maximum amount of product possible from limiting reactant.

• Example: If 2 mol H2 and 1 mol O2 react, H2 is limiting for $2H_2 + O_2 \rightarrow 2H_2O$.

Dilution Calculations

Dilution involves adding solvent to decrease concentration.

• Use the formula: $M_1V_1 = M_2V_2$

• Example: To dilute 50 mL of 2 M solution to 1 M: $2 \times 50 = 1 \times V_2 \Rightarrow V_2 = 100\ mL$

Chapter 9: Energy, Equilibrium, and Acids & Bases

Potential and Kinetic Energy

Energy in chemical systems can be stored (potential) or in motion (kinetic).

• Potential energy: Stored energy due to position or composition.

• Kinetic energy: Energy of motion.

• Breaking bonds requires energy (endothermic); forming bonds releases energy (exothermic).

Endothermic vs. Exothermic Reactions

• Endothermic: Absorbs heat; products have higher energy than reactants.

• Exothermic: Releases heat; products have lower energy than reactants.

• Energy diagrams show the energy change during a reaction.

Chemical Equilibrium

At equilibrium, the rate of the forward reaction equals the rate of the reverse reaction.

• Equilibrium constant (K): $K = \frac{[\text{products}]}{[\text{reactants}]}$

• Le Châtelier’s Principle: If a system at equilibrium is disturbed, it will shift to counteract the disturbance.

Acids and Bases

• Bronsted-Lowry definition: Acids donate protons (H+), bases accept protons.

• Strong acids/bases: Completely ionize in water (e.g., HCl, NaOH).

• Weak acids/bases: Partially ionize (e.g., acetic acid, ammonia).

• Acid dissociation constant (Ka): $K_a = \frac{[A^-][H_3O^+]}{[HA]}$

• pH: $pH = -\log[H_3O^+]$

• pKa: $pK_a = -\log K_a$

• Buffer: A solution that resists pH change, made from a weak acid and its conjugate base.

• Neutralization: Acid + base → salt + water.

Acid-Base Calculations

• Water dissociation constant: $K_w = [H_3O^+][OH^-] = 1.0 \times 10^{-14}$

• Relationship: $[H_3O^+][OH^-] = 10^{-14}$

• pH and pOH: $pH + pOH = 14$

• Henderson-Hasselbalch equation: $pH = pK_a + \log \frac{[A^-]}{[HA]}$

Acid Dissociation Constants Table

The following table lists common acids and their $K_a$ values, which indicate acid strength (lower $K_a$ = weaker acid):

Acid	Formula	$K_a$
Phosphoric acid	H3PO4	7.5 × 10-3
Nitrous acid	HNO2	4.5 × 10-4
Hydrofluoric acid	HF	3.5 × 10-4
Formic acid	HCO2H	1.8 × 10-4
Acetic acid	CH3COOH	1.8 × 10-5
Carbonic acid	H2CO3	4.3 × 10-7
Hydrosulfuric acid	H2S	9.1 × 10-8
Dihydrogen phosphate ion	H2PO4-	6.2 × 10-8
Hydrocyanic acid	HCN	4.9 × 10-10
Bicarbonate ion	HCO3-	5.6 × 10-11
Hydrogen phosphate	HPO42-	2.2 × 10-13

Chapter 13: Hydrocarbons and Organic Chemistry Basics

Hydrocarbons: Structure and Properties

Hydrocarbons are organic compounds consisting of only carbon and hydrogen.

• Alkanes: Saturated hydrocarbons with single bonds (C–C).

• Alkenes: Unsaturated hydrocarbons with at least one double bond (C=C).

• Alkynes: Unsaturated hydrocarbons with at least one triple bond (C≡C).

• Solubility: Hydrocarbons are generally nonpolar and insoluble in water.

Structural Formulas and Isomerism

• Condensed structural formula: Shows the arrangement of atoms without all bonds.

• Line structure: Simplified organic structure where lines represent bonds between carbon atoms.

• Isomers: Molecules with the same molecular formula but different structures.

• Cis-trans isomerism: Occurs in alkenes due to restricted rotation around double bonds.

Naming and Identifying Hydrocarbons

• Use IUPAC rules to name hydrocarbons based on the longest carbon chain and substituents.

• Identify the structure from the name and vice versa.

• Determine molecular formula from line or condensed structure.

Reactions of Hydrocarbons

• Halogenation: Replacement of hydrogen with a halogen (e.g., Cl, Br).

• Identify possible products when given a reactant and reaction conditions.

• Know the three positions for disubstituted benzenes: ortho (1,2-), meta (1,3-), para (1,4-).

Appendix: Key Equations and Constants

• Avogadro's number: $1\ mol = 6.02 \times 10^{23}$ (atoms, molecules, or ions)

• Molarity (M): $M = \frac{\text{mol}}{L}$

• Dilution: $M_1V_1 = M_2V_2$

• Equilibrium constant: $K = \frac{[\text{products}]}{[\text{reactants}]}$

• Water dissociation: $K_w = [H_3O^+][OH^-] = 1.0 \times 10^{-14}$

• pH: $pH = -\log[H_3O^+]$

• pK_a: $pK_a = -\log K_a$

• Henderson-Hasselbalch: $pH = pK_a + \log \frac{[A^-]}{[HA]}$

Appendix: Periodic Table

The periodic table organizes elements by increasing atomic number and groups elements with similar chemical properties. It is essential for determining atomic masses, valence electrons, and predicting chemical behavior.

Additional info: The study guide covers foundational GOB Chemistry topics, including chemical reactions, stoichiometry, acids and bases, equilibrium, and introductory organic chemistry. The included tables and equations are essential for problem-solving and conceptual understanding in a GOB Chemistry course.