General Chemistry Exam Study Guide For Exam 3

Introduction

This study guide summarizes the key topics and concepts for an upcoming General Chemistry exam, focusing on gases, thermodynamics, and calorimetry. It outlines essential definitions, laws, equations, and problem-solving strategies that students should master.

Oxidation-Reduction Reactions

Definitions and Identification

• Oxidation: The loss of electrons by a substance.

• Reduction: The gain of electrons by a substance.

• Oxidizing Agent: The substance that causes oxidation by accepting electrons.

• Reducing Agent: The substance that causes reduction by donating electrons.

• Be able to assign oxidation states to elements in compounds and ions.

• Identify which species are oxidized and reduced in a reaction.

Example: In the reaction Zn + Cu2+ → Zn2+ + Cu, Zn is oxidized and Cu2+ is reduced.

Gases

Properties and Laws

• Understand the properties of gases and how they differ from solids and liquids.

• Know the standard temperature and pressure (STP): 0°C (273.15 K) and 1 atm.

Gas Laws

• Boyle's Law: At constant temperature, the pressure and volume of a gas are inversely related.

• Charles's Law: At constant pressure, the volume of a gas is directly proportional to its temperature (in Kelvin).

• Avogadro's Law: At constant temperature and pressure, the volume of a gas is directly proportional to the number of moles.

• Ideal Gas Law: Relates pressure, volume, temperature, and moles of a gas. Where R is the universal gas constant.

Applications of Gas Laws

• Calculate molar volume at STP: 1 mol of gas = 22.4 L at STP.

• Use the ideal gas law to determine the density or molar mass of a gas.

Mixtures of Gases and Partial Pressures

• Dalton's Law of Partial Pressures: The total pressure of a mixture of gases equals the sum of the partial pressures of each component.

• Calculate mole fractions and partial pressures in mixtures.

Stoichiometry Involving Gases

• Be able to perform stoichiometric calculations using gas laws.

Kinetic Molecular Theory (KMT)

• Describes the behavior of ideal gases at the molecular level.

• Relates temperature to the average kinetic energy of gas particles.

• Explains properties such as pressure and diffusion.

Graham's Law of Effusion and Diffusion

• Describes the rate at which gases effuse (escape through a small hole) or diffuse (spread out).

• Graham's Law: Where and are the molar masses of the gases.

• Use Graham's Law to calculate unknown molar masses.

Real Gases: Deviations from Ideal Behavior

• Real gases deviate from ideal behavior at high pressures and low temperatures.

• Van der Waals equation corrects for intermolecular forces and molecular volume: Where and are constants for each gas.

Thermodynamics

Definitions and Laws

• Thermodynamics: The study of energy changes in chemical reactions.

• System: The part of the universe being studied; Surroundings: Everything else.

• First Law of Thermodynamics (Law of Conservation of Energy): Energy cannot be created or destroyed, only transferred or transformed. Where is the change in internal energy, is heat, and is work.

• Sign conventions: and are positive if energy flows into the system, negative if energy flows out.

Types of Energy

• Kinetic Energy: Energy of motion.

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

• Thermal Energy: Energy associated with temperature.

Work and Heat

• Work done by or on a system: Where is pressure and is the change in volume.

• Heat capacity (): Amount of heat required to raise the temperature of a substance by 1°C. Specific heat capacity (): Heat required to raise 1 g of a substance by 1°C. Where is mass, is specific heat, and is the temperature change.

Calorimetry

• Measurement of heat flow in chemical reactions.

• Constant Volume Calorimetry (Bomb Calorimeter): Measures (heat at constant volume).

• Constant Pressure Calorimetry (Coffee Cup Calorimeter): Measures (heat at constant pressure).

• Relationship:

Enthalpy ()

• Enthalpy is the heat content of a system at constant pressure.

• (heat at constant pressure).

• Endothermic reactions: (heat absorbed).

• Exothermic reactions: (heat released).

Hess's Law

• The enthalpy change for a reaction is the same, regardless of the number of steps.

• Apply Hess's Law to calculate for complex reactions by combining known enthalpy changes.

Sample Table: Gas Laws Comparison

Additional Exam Information

• You will be provided with a periodic table, equation sheet, and scratch paper.

• Bring a non-programmable, non-graphing calculator and a #2 pencil.

• Exam format: 50 minutes, 25 multiple choice questions (+10 calculation-based questions).

• No other aids or personal items allowed except pencil and calculator.

Additional info: Some context and definitions have been expanded for clarity and completeness.