CHEM 121A: Thermochemistry and Electronic Structure of Atoms

Comprehensive vocabulary flashcards covering thermochemistry principles, state functions, calorimetry, electromagnetic radiation, quantum models, and electronic structure rules for General Chemistry I.

Thermochemistry

The study of energy and its transformations, typically measured in joules ($\text{J}$) or kilojoules ($\text{kJ}$), where $1\,\text{J} = 1\,\frac{\text{kg}\cdot\text{m}^2}{\text{s}^2}$.

First Law of Thermodynamics

The thermodynamic law stating that energy is neither created nor destroyed, flowing between the system and surroundings and back again.

System and Surroundings

The system is the specific portion of the universe under study, while the surroundings encompass everything else outside of that system (such as the cylinder, piston, and external environment).

Heat ($q$)

The flow of energy caused by a difference in temperature; it always flows spontaneously from hot to cold and is distinct from temperature itself.

Work ($w$)

The energy transfer resulting from the displacement of an object by an applied force, represented mathematically as $w = F \times d$.

Internal Energy ($E$)

The sum of all kinetic and potential energies present within a system, where changes in energy are given by $\Delta E = q + w$.

State Function

A thermodynamic property whose value depends only on the present condition and state of the system, rather than the pathway taken to reach that state (e.g., $\Delta E = E_{\text{final}} - E_{\text{initial}}$).

Enthalpy ($H$)

A state function ($\Delta H = H_{\text{final}} - H_{\text{initial}}$) measuring the heat flow occurring under constant-pressure conditions, defined as $\Delta H = q_P$.

Exothermic Reaction

A process in which a chemical system releases heat to its surroundings, resulting in a negative enthalpy change ($-\Delta H$) and a warm-to-the-touch sensation (e.g., hand warmers).

Endothermic Reaction

A process in which a chemical system absorbs heat from its surroundings, resulting in a positive enthalpy change ($+\Delta H$) and a cold-to-the-touch sensation (e.g., emergency ice packs).

Standard Enthalpy of Formation ($\Delta H_f^\circ$)

The enthalpy change associated with forming one mole of a compound from its constituent elements in their standard states at $1\,\text{atm}$ and $298\,\text{K}$.

Hess's Law

The principle stating that if a reaction is carried out in a series of steps, the overall enthalpy change ($\Delta H_{\text{overall}}$) will equal the sum of the enthalpy changes of the individual elementary reactions.

Bond Enthalpy

The enthalpy change required to break a particular chemical bond in one mole of a gaseous substance, used to estimate reaction enthalpy by $\Delta H_{\text{rxn}} = \sum(\text{bonds broken}) - \sum(\text{bonds formed})$.

Calorimetry

The experimental measurement of heat flow in physical and chemical processes using the heat capacity of the system or solvent alongside observed temperature changes.

Heat Capacity ($C$)

The quantity of heat needed to raise the temperature of a given substance or body by $1\,\text{K}$ (or $1\,^\circ\text{C}$).

Specific Heat Capacity ($C_s$)

The quantity of heat required to increase the temperature of $1\,\text{g}$ of a substance by $1\,\text{K}$ (or $1\,^\circ\text{C}$), calculated via $q = m \times C_s \times \Delta T$.

Coffee-Cup Calorimeter

A constant-pressure calorimeter setup consisting of nested Styrofoam cups, a lid/cork stopper, a stirrer, and a thermometer used to measure aqueous heat flow where $\Delta H_{\text{rxn}} = -m_{\text{soln}} \times C_{s,\text{soln}} \times \Delta T_{\text{soln}}$.

Bomb Calorimeter

A constant-volume apparatus used to measure heat released during combustion reactions by monitoring the temperature change of the surrounding water bath, governed by $q_{\text{rxn}} = -C_{\text{cal}} \times \Delta T$.

Electromagnetic Radiation

Energy and radiation generated by particles traveling through space in characteristic wave patterns, defined by speed ($c$), wavelength ($\lambda$), and frequency ($\nu$).

Wavelength ($\lambda$)

The distance between consecutive peaks or crests of a wave.

Frequency ($\nu$)

The number of complete wave cycles that pass a given point in one second, expressed in units of Hertz ($\text{Hz}$) or $1/\text{s}$.

Speed of Light ($c$)

The constant speed at which all electromagnetic radiation travels in a vacuum, equal to $2.99 \times 10^8\,\text{m/s}$, relating frequency and wavelength via $c = \lambda\nu$.

Wave-Particle Duality

The quantum concept describing how light and matter exhibit behaviors characteristic of both continuous waves and discrete particles depending on the experimental observation.

Photon

A discrete packet or quantum of electromagnetic energy whose energy content is determined by Planck's equation, $E = h\nu = \frac{hc}{\lambda}$.

Photoelectric Effect

The emission of electrons from a metal surface that occurs only when light at or above a specific threshold frequency strikes the surface.

Continuous Spectrum

An uninterrupted emission spectrum that contains all wavelengths of light across a visible range without gaps or blank lines.

Line Spectrum

A spectrum that contains radiation at only specific, discrete wavelengths produced when electrons undergo transitions between discrete atomic energy levels.

Bohr Model

A model of the hydrogen atom describing quantized circular orbits where the electron energy is defined by $E = -2.18 \times 10^{-18}\left(\frac{1}{n^2}\right)\,\text{J}$.

Heisenberg Uncertainty Principle

The fundamental quantum principle stating that it is inherently impossible to simultaneously determine both the exact position and momentum of an electron.

de Broglie Wavelength

The wavelength associated with any moving matter particle of mass $m$ and velocity $v$, defined by $\lambda = \frac{h}{mv}$.

Orbital

A three-dimensional mathematical wavefunction describing the region of space around a nucleus that encloses a $90\%$ probability of finding an electron.

Principal Quantum Number ($n$)

The quantum number ($n = 1, 2, 3\dots$) indicating the main electron shell, which determines the overall size and energy of the orbital.

Angular Momentum Quantum Number ($l$)

The quantum number ranging from $0$ to $n - 1$ that specifies the three-dimensional geometric shape of an orbital ($l = 0 \rightarrow s$, $l = 1 \rightarrow p$, $l = 2 \rightarrow d$, $l = 3 \rightarrow f$).

Magnetic Quantum Number ($m_l$)

The quantum number ranging from $-l$ to $+l$ that specifies the spatial orientation of an orbital relative to the Cartesian axes.

Spin Quantum Number ($m_s$)

The quantum number describing the intrinsic angular momentum of an electron, taking values of $+\frac{1}{2}$ (spin up) or $-\frac{1}{2}$ (spin down).

Node

A point or region in an orbital where the electron wavefunction ($\psi$) equals zero, representing zero probability of finding an electron.

d Orbitals

A set of five orbitals corresponding to $l = 2$ ($d_{yz}$, $d_{xz}$, $d_{xy}$, $d_{x^2-y^2}$, and $d_{z^2}$) that feature two nodal surfaces.

Pauli Exclusion Principle

The quantum rule stating that no two electrons within an atom can have identical sets of all four quantum numbers ($n$, $l$, $m_l$, $m_s$), limiting any orbital to two electrons of opposite spin.

Hund's Rule

The rule establishing that when electrons enter degenerate orbitals, maximum stability is achieved by filling each orbital singly with parallel spins before pairing occurs.

Degenerate Orbitals

Orbitals belonging to the same subshell that have identical energy levels in an isolated atom.

Core Electrons

Inner-shell electrons that correspond to a preceding noble gas configuration and are not involved in chemical bonding.

Valence Electrons

Electrons located in the outermost principal energy level (highest $n$ value) that participate directly in chemical bonding.