General Chemistry Practice Final Exam Study Notes

Liquids, Solids, and Intermolecular Forces

Vapor Pressure and Boiling Point

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid at a given temperature. The boiling point of a liquid is the temperature at which its vapor pressure equals atmospheric pressure.

• Vapor Pressure: Increases with temperature as more molecules have enough energy to escape the liquid phase.

• Boiling Point: The temperature at which vapor pressure equals 1 atm (normal boiling point).

• Intermolecular Forces: Substances with stronger intermolecular forces have lower vapor pressures and higher boiling points.

• Example: Water has a higher boiling point than ethanol due to stronger hydrogen bonding.

Table: Comparison of Vapor Pressure Curves

Substance	Normal Boiling Point (°C)	Relative Vapor Pressure
Diethyl Ether	34.6	High
Ethanol	78.3	Medium
Water	100	Low
Ethylene Glycol	197	Very Low

Additional info: The graph shown compares vapor pressure curves for several liquids, illustrating how boiling point increases as intermolecular forces become stronger.

Thermochemistry

Enthalpy and Energy Calculations

Thermochemistry involves the study of energy changes during chemical reactions, particularly heat exchange. The enthalpy change ($\Delta H$) is a key concept in determining whether a reaction is exothermic or endothermic.

• Enthalpy ($\Delta H$): The heat content of a system at constant pressure.

• Exothermic Reaction: Releases heat ($\Delta H < 0$).

• Endothermic Reaction: Absorbs heat ($\Delta H > 0$).

• Standard Enthalpy of Formation ($\Delta H_f^\circ$): The enthalpy change when one mole of a compound is formed from its elements in their standard states.

• Equation:

$\Delta H_{rxn} = \sum \Delta H_f^\circ (\text{products}) - \sum \Delta H_f^\circ (\text{reactants})$

Example: Calculating the enthalpy change for the combustion of methane using standard enthalpies of formation.

Gases

Gas Laws and Calculations

The behavior of gases is described by several laws that relate pressure, volume, temperature, and amount of gas.

• Ideal Gas Law: $PV = nRT$

• Boyle's Law: $P_1V_1 = P_2V_2$ (at constant T and n)

• Charles's Law: $\frac{V_1}{T_1} = \frac{V_2}{T_2}$ (at constant P and n)

• Avogadro's Law: $\frac{V_1}{n_1} = \frac{V_2}{n_2}$ (at constant P and T)

• Units: Pressure (atm, mmHg), Volume (L), Temperature (K), Amount (mol)

• Example: Calculating the volume of a gas at STP given moles.

Solutions and Aqueous Reactions

Concentration and Solution Properties

Solutions are homogeneous mixtures of two or more substances. The concentration of a solution is commonly expressed in molarity (M).

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

• Types of Solutions: Saturated, unsaturated, supersaturated

• Colligative Properties: Depend on the number of solute particles (e.g., boiling point elevation, freezing point depression)

• Example: Calculating the molarity of NaCl in a solution.

Chemical Equilibrium

Equilibrium Constant and Calculations

Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal. The equilibrium constant ($K$) expresses the ratio of product concentrations to reactant concentrations at equilibrium.

• Equilibrium Constant ($K$): $K = \frac{[\text{products}]}{[\text{reactants}]}$ (raised to the power of their coefficients)

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

• Example: Predicting the shift in equilibrium when concentration or temperature changes.

Acids and Bases

Definitions and Calculations

Acids and bases are defined by their ability to donate or accept protons (Brønsted-Lowry) or produce H+ or OH- ions (Arrhenius).

• pH Calculation: $pH = -\log[H^+]$

• Strong vs. Weak Acids/Bases: Strong acids/bases dissociate completely; weak acids/bases only partially.

• Example: Calculating the pH of a 0.01 M HCl solution.

Additional info:

Some content and questions were inferred from the context of a practice final exam and the visible vapor pressure graph. The study notes cover key topics relevant to General Chemistry, including phase changes, thermochemistry, gas laws, solutions, equilibrium, and acids/bases, as these are commonly tested in final exams.