General Chemistry Final Exam Review: Thermochemistry, Atomic Structure, and Periodic Properties

Thermochemistry

Endothermic and Exothermic Reactions

Thermochemistry studies the energy changes that occur during chemical reactions. Reactions are classified as endothermic or exothermic based on heat flow.

• Endothermic reactions: Absorb heat from the surroundings; the system gains energy.

• Exothermic reactions: Release heat to the surroundings; the system loses energy.

• Example: Combustion of methane is exothermic; melting of ice is endothermic.

System and Surroundings

The system is the part of the universe under study (e.g., the chemicals in a reaction vessel), while the surroundings are everything else.

• Energy exchange occurs between the system and surroundings as heat (q) or work (w).

Units of Heat and Specific Heat Capacity

• Heat (q) units: Joule (J), calorie (cal), kilocalorie (kcal)

• 1 cal = 4.184 J; 1 kcal = 1000 cal

• Specific heat capacity (c): Amount of heat required to raise the temperature of 1 g of a substance by 1°C (or 1 K). Units: J/g·°C or J/g·K

Calculating Kinetic Energy

Kinetic energy (KE) of an object is given by:

$KE = \frac{1}{2}mv^2$

• m = mass (kg), v = velocity (m/s)

• Example: Calculate the kinetic energy of a car (mass = 1575 kg) moving at 89.5 km/h.

Calculating Heat Transfer

The heat (q) absorbed or released by a substance is calculated as:

$q = m \cdot c \cdot \Delta T$

• m = mass (g), c = specific heat (J/g·°C), $\Delta T$ = change in temperature (°C)

• Example: Calculate the heat required to raise 25 g of Fe from 37°C to 75°C, given $c = 0.57$ J/g·°C.

Electromagnetic Radiation

• Types of radiation: radio, microwave, infrared, visible, ultraviolet, X-ray, gamma ray

• Frequency ($\nu$), wavelength ($\lambda$), and speed of light (c) are related by:

$c = \lambda \nu$

• c = speed of light ($3.00 \times 10^8$ m/s)

Atomic Structure and Electron Configuration

Subshells and Orbitals

Each principal energy level (n) contains n subshells. Subshells are labeled s, p, d, f.

Shell (n)	Number of Subshells	Types of Subshells
1	1	1s
2	2	2s, 2p
3	3	3s, 3p, 3d
4	4	4s, 4p, 4d, 4f

• s: 1 orbital, 2 electrons

• p: 3 orbitals, 6 electrons

• d: 5 orbitals, 10 electrons

• f: 7 orbitals, 14 electrons

Electron Configuration

• Filling order: 1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s → 4f → 5d → 6p → 7s → 5f → 6d → 7p

• Hund's rule, Pauli exclusion principle, and Aufbau principle govern electron filling.

• Transition metals may have exceptions due to stability of half-filled and fully-filled d subshells.

Quantum Numbers

• Principal quantum number (n): energy level

• Angular momentum quantum number (l): subshell (s=0, p=1, d=2, f=3)

• Magnetic quantum number ($m_l$): orientation

• Spin quantum number ($m_s$): +1/2 or -1/2

Periodic Properties of the Elements

Trends in the Periodic Table

• Atomic radius: Increases down a group, decreases across a period.

• Ionization energy: Energy required to remove an electron; increases across a period, decreases down a group.

• Electron affinity: Energy change when an atom gains an electron; generally more negative across a period.

• Metallic character: Increases down a group, decreases across a period.

Group and Period Similarities

• Elements in the same group have similar chemical properties due to similar valence electron configurations.

Metallic and Nonmetallic Oxides

• Metallic oxides (e.g., Na2O, K2O) form basic solutions in water.

• Nonmetallic oxides (e.g., CO2, SO2, NO2) form acidic solutions in water.

Thermodynamics and Hess's Law

First Law of Thermodynamics

Energy cannot be created or destroyed; it can only be transferred or transformed.

• Internal energy change ($\Delta U$) is the sum of heat (q) and work (w):

$\Delta U = q + w$

Enthalpy ($\Delta H$)

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

• Exothermic: $\Delta H$ is negative (heat released)

• Endothermic: $\Delta H$ is positive (heat absorbed)

Hess's Law

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

• If a reaction is reversed, the sign of $\Delta H$ is reversed.

• If a reaction is multiplied by a factor, $\Delta H$ is multiplied by the same factor.

Practice Problems and Applications

• Identify endothermic/exothermic processes from reaction equations.

• Calculate enthalpy changes using Hess's Law.

• Determine which elements have similar chemical properties based on group/period.

• Predict trends in atomic radius, ionization energy, and electron affinity.

• Classify oxides as acidic or basic based on their metallic or nonmetallic nature.

• Apply quantum numbers to determine electron configurations and subshell capacities.

Key Equations and Constants

• $q = m \cdot c \cdot \Delta T$

• $KE = \frac{1}{2}mv^2$

• $c = \lambda \nu$

• 1 cal = 4.184 J

• Speed of light, $c = 3.00 \times 10^8$ m/s

Additional info:

• Students should be familiar with the periodic table and be able to identify trends and exceptions, especially for transition metals.

• Understanding the relationship between electronic structure and chemical properties is essential for predicting reactivity and bonding.