"The internal energy of a thermodynamic system is the energy contained within it, measured as the quantity of energy necessary to bring the system from its standard internal state to its present internal state of interest..."
Introducing internal energy and enthalpy as thermodynamic properties of a system, along with their relationship to work and heat.
System and surroundings: A thermodynamic system is the part of the universe being studied, while the surroundings are the rest of the universe. This distinction is necessary for understanding the transfer of energy between the system and its surroundings.
First law of thermodynamics: The first law of thermodynamics is a statement of the conservation of energy. It states that energy can neither be created nor destroyed, but can only be converted from one form to another.
Internal energy: Internal energy is the total energy possessed by the molecules of a system. It includes kinetic energy, potential energy, and chemical energy.
Enthalpy: Enthalpy is a thermodynamic quantity that measures the heat content of a system. It is equal to the internal energy plus the work done by the system against external pressure.
State functions: State functions are thermodynamic properties that depend only on the state of the system, not on how the system reached that state. Internal energy and enthalpy are examples of state functions.
Heat and work: Heat and work are both forms of energy transfer. Heat is the transfer of energy due to temperature differences, while work is the transfer of energy that results from an external force acting on a system.
Specific heat: Specific heat is a measure of the amount of heat needed to raise the temperature of a unit mass of a substance by a given amount.
Heat capacity: Heat capacity is a measure of the amount of heat needed to raise the temperature of a system by a given amount.
Enthalpy of reaction: The enthalpy of reaction is the heat released or absorbed during a chemical reaction.
Enthalpy of formation: The enthalpy of formation is the heat released or absorbed when one mole of a substance is formed from its constituent elements.
Enthalpy of combustion: The enthalpy of combustion is the heat released or absorbed when a substance is burned in oxygen.
Enthalpy of solution: The enthalpy of solution is the heat released or absorbed when a solute is dissolved in a solvent.
Hess's law: Hess's law states that the enthalpy change for a reaction is independent of the pathway taken to reach the final products.
Standard enthalpy of formation: The standard enthalpy of formation is the enthalpy change that occurs when one mole of a substance is formed from its constituent elements under standard conditions.
Standard state: The standard state is a set of conditions (temperature, pressure, and concentration) that are commonly used as reference states for thermodynamic calculations.
Sensible Energy: The energy that a substance possesses due to its temperature.
Latent Energy: The energy that a substance possesses during phase changes, such as during melting or vaporization.
Chemical Energy: The energy that a substance possesses as a result of its chemical composition and atomic/molecular structure.
Nuclear Energy: The energy that a substance possesses as a result of its atomic and subatomic structure.
Potential Energy: The energy that a substance possesses due to its position within a field or gravitational force.
Kinetic Energy: The energy that a substance possesses due to its motion.
Internal Energy: The total energy within a system, including its kinetic and potential energies.
Enthalpy: The measure of a system's total energy, including the internal energy and any additional work done by the system.
Free Energy: The energy available for a system to perform work when held at constant temperature and pressure.
Helmholtz Energy: The energy available for a system to perform work when held at constant volume and temperature.
"It excludes the kinetic energy of motion of the system as a whole and the potential energy of position of the system as a whole, with respect to its surroundings and external force fields."
"The internal energy of an isolated system cannot change, as expressed in the law of conservation of energy, a foundation of the first law of thermodynamics."
"The processes that change the internal energy are transfers, into or out of the system, of matter, or of energy, as heat, or by thermodynamic work. These processes are measured by changes in the system's properties, such as temperature, entropy, volume, electric polarization, and molar constitution."
"The internal energy cannot be measured absolutely. Thermodynamics concerns changes in the internal energy, not its absolute value."
"The internal energy depends only on the internal state of the system and not on the particular choice from many possible processes by which energy may pass into or out of the system."
"In statistical mechanics, the internal energy of a body can be analyzed microscopically in terms of the kinetic energies of microscopic motion of the system's particles..."
"The processes that change the internal energy are transfers, into or out of the system, of matter, or of energy, as heat, or by thermodynamic work."
"These processes are measured by changes in the system's properties, such as temperature, entropy, volume, electric polarization, and molar constitution."
"It is a state variable, a thermodynamic potential, and an extensive property."
"The unit of energy in the International System of Units (SI) is the joule (J)."
"The internal energy relative to the mass with unit J/kg is the specific internal energy."
"The corresponding quantity relative to the amount of substance with unit J/mol is the molar internal energy."
"... accounting for the gains and losses of energy due to changes in its internal state, including such quantities as magnetization."
"It excludes the kinetic energy of motion of the system as a whole and the potential energy of position of the system as a whole, with respect to its surroundings and external force fields."
"It includes the thermal energy, i.e., the constituent particles' kinetic energies of motion relative to the motion of the system as a whole."
"The internal energy of an isolated system cannot change, as expressed in the law of conservation of energy, a foundation of the first law of thermodynamics."
"Thermodynamics concerns changes in the internal energy, not its absolute value."
"The internal energy depends only on the internal state of the system and not on the particular choice from many possible processes by which energy may pass into or out of the system."
"...the kinetic energies of microscopic motion of the system's particles from translations, rotations, and vibrations, and of the potential energies associated with microscopic forces, including chemical bonds."