CHEM162 Midterm Exam Study Guide: Key Concepts in General Chemistry

States and Classification of Matter

States of Matter and Classification

The physical world is composed of matter, which exists in different states and can be classified based on its properties and composition.

• States of Matter: Solid, liquid, and gas are the three primary states, each with distinct particle arrangements and energy levels.

• Classification: Matter can be classified as pure substances (elements and compounds) or mixtures (homogeneous and heterogeneous).

• Homogeneous Mixtures: Uniform composition throughout (e.g., saltwater).

• Heterogeneous Mixtures: Non-uniform composition (e.g., salad, sand in water).

• Example: Air is a homogeneous mixture, while granite is heterogeneous.

Laws of Chemistry

Conservation of Mass, Definite and Multiple Proportions

Several fundamental laws govern chemical reactions and the composition of substances.

• Law of Conservation of Mass: Mass is neither created nor destroyed in a chemical reaction.

• Law of Definite Proportions: A chemical compound always contains the same elements in the same proportion by mass.

• Law of Multiple Proportions: When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in ratios of small whole numbers.

• Example: CO and CO2 both contain carbon and oxygen, but in different ratios.

Atomic Theory and Structure

Discovery of Subatomic Particles, Dalton's Model

The atomic theory describes the nature of atoms and their internal structure.

• Dalton's Atomic Theory: Atoms are indivisible particles that make up elements; atoms of the same element are identical.

• Discovery of Subatomic Particles: Atoms are composed of protons, neutrons, and electrons.

• Atomic Number (Z): Number of protons in the nucleus.

• Mass Number (A): Total number of protons and neutrons.

• Isotopes: Atoms of the same element with different numbers of neutrons.

• Example: Carbon-12 and Carbon-14 are isotopes of carbon.

Mole Concept and Avogadro's Number

Counting Atoms and Molecules

The mole is a fundamental unit in chemistry for counting particles.

• Mole (mol): The amount of substance containing as many entities as there are atoms in 12 g of carbon-12.

• Avogadro's Number: $6.022 \times 10^{23}$ particles/mol.

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

• Example: 1 mol of H2O contains $6.022 \times 10^{23}$ molecules and has a mass of 18.02 g.

Energy Concepts in Chemistry

Endothermic and Exothermic Processes, Heat Transfer

Chemical reactions involve energy changes, often in the form of heat.

• Endothermic Process: Absorbs energy from surroundings (e.g., melting ice).

• Exothermic Process: Releases energy to surroundings (e.g., combustion).

• Heat Transfer: Energy flows from high to low temperature.

• Enthalpy Change ($\Delta H$): $\Delta H = H_{products} - H_{reactants}$

• Example: Burning methane is exothermic; photosynthesis is endothermic.

Thermochemistry

Calorimetry, Enthalpy, Hess's Law, Bond Energies

Thermochemistry studies the heat involved in chemical processes.

• Calorimetry: Measurement of heat flow using a calorimeter.

• Specific Heat Capacity ($c$): $q = mc\Delta T$

• Hess's Law: The total enthalpy change is the same, regardless of the pathway.

• Bond Energies: Energy required to break one mole of a bond in a molecule.

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

• Example: Calculating $\Delta H$ for a reaction using bond energies or Hess's Law.

Gas Laws and Kinetic Molecular Theory

Gas Properties, Laws, and Molecular Behavior

Gases exhibit unique behaviors described by several empirical laws and theoretical models.

• Pressure ($P$): Force per unit area exerted by gas particles.

• Volume ($V$): Space occupied by the gas.

• Temperature ($T$): Measure of average kinetic energy.

• Ideal Gas Law: $PV = nRT$

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

• Charles's Law: $V_1/T_1 = V_2/T_2$ (at constant $P$ and $n$)

• Avogadro's Law: $V_1/n_1 = V_2/n_2$ (at constant $P$ and $T$)

• Dalton's Law of Partial Pressures: $P_{total} = P_1 + P_2 + ... + P_n$

• Kinetic Molecular Theory: Explains gas behavior in terms of particle motion and collisions.

• Root Mean Square Velocity ($u_{rms}$): $u_{rms} = \sqrt{\frac{3RT}{M}}$

• Diffusion: Mixing of gases due to molecular motion.

• Effusion: Escape of gas through a small hole.

• Real Gases: Deviate from ideal behavior at high pressure and low temperature.

• Example: Calculating the pressure of a gas mixture using Dalton's Law.

Summary Table: Key Gas Laws

Law	Equation	Variables Held Constant
Boyle's Law	$P_1V_1 = P_2V_2$	Temperature, amount of gas
Charles's Law	$V_1/T_1 = V_2/T_2$	Pressure, amount of gas
Avogadro's Law	$V_1/n_1 = V_2/n_2$	Pressure, temperature
Ideal Gas Law	$PV = nRT$	None (general relationship)
Dalton's Law	$P_{total} = \sum P_i$	Volume, temperature

Additional info:

• Some subtopics (e.g., "energy exchange work," "enthalpy of reaction") are included under broader headings for clarity.

• All equations are provided in standard LaTeX format for clarity and study purposes.