"In thermodynamics, enthalpy is the sum of a thermodynamic system's internal energy and the product of its pressure and volume."
Understanding enthalpy, heat, and calorimetry, including the calculation of heat exchanged or absorbed, Hess's law, and standard enthalpy of formation and reaction.
Stoichiometry: The study of the quantitative relationships between reactants and products in chemical reactions.
Enthalpy: A thermodynamic property that measures the amount of heat absorbed or released during a process.
Entropy: A thermodynamic property that measures the degree of disorder in a system.
Gibbs Free Energy: A thermodynamic property that determines whether a process is spontaneous or not.
Hess's Law: A law that states that the total enthalpy change in a reaction is independent of the pathway taken.
Calorimetry: The measurement of heat flow in a system.
Heat of Formation: The heat absorbed or released when one mole of a compound is formed from its constituent elements.
Heat of Reaction: The heat absorbed or released during a chemical reaction.
Standard Enthalpy of Formation: The enthalpy change that occurs when one mole of a compound is formed from its elements at standard state.
Bond Energy: The energy required to break a chemical bond.
Heat Capacity: The amount of heat required to raise the temperature of a substance by one degree.
Internal Energy: The sum of the kinetic and potential energies of the particles in a system.
Partial Pressure: The pressure exerted by one component of a mixture of gases.
Phase Changes: The transitions between solid, liquid, and gas phases that involve the absorption or release of energy.
Van't Hoff Factor: The number of particles into which a solute dissociates in a solution.
Thermodynamics Laws (1st & 2nd): The first law of thermodynamics is the law of conservation of energy. The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time.
Standard Entropy: A measure of the degree of disorder for a substance at standard state.
Kirchhoff’s Laws: Two fundamental laws of thermodynamics that deal with the changes in enthalpy and entropy of a reaction during changes in temperature.
Heat Transfer: The process by which thermal energy is exchanged between two bodies.
Exothermic and Endothermic Reactions: Reactions where heat is released (Exothermic) or absorbed (Endothermic).
Chemical Potential: The Gibbs free energy per particle in a system.
Ideal Gas Law: A fundamental law that describes the behavior of ideal gases.
Law of Mass Action: A generalization of the simple equilibrium concept to include the effects of pressure, temperature and concentration variations among reacting species.
Phase Equilibria: The state of a physical system at which the composition and properties of each phase do not vary with time.
Standard Reaction Entropy: The entropy change that occurs in a reaction at a standard state.
Enthalpy: The heat absorbed or released during a chemical reaction at constant pressure.
Specific heat: The amount of heat required to raise the temperature of a substance by one degree Celsius per unit mass.
Heat capacity: The amount of heat required to raise the temperature of a substance by one degree Celsius per unit quantity.
Calorimetry: The measurement of heat changes during chemical reactions or physical changes.
Hess's Law: The enthalpy change of a reaction is independent of the pathway taken from reactants to products.
Bond energy: The amount of energy required to break a specific bond in one mole of a compound.
Heat of formation: The enthalpy change when one mole of a compound is formed from its constituent elements in their standard states.
Kirchhoff's Law: The dependence of thermodynamic quantities on temperature.
Standard enthalpy of reaction: The enthalpy change when one mole of a compound reacts completely with a limiting reactant under standard conditions.
Calorific value: The amount of heat released when one unit of substance is burnt completely.
Standard enthalpy of formation: The enthalpy change when one mole of a compound is formed from its constituent elements in their standard states.
Adiabatic calorimetry: The measurement of heat released or absorbed during a chemical reaction, using adiabatic conditions.
Thermochemical equation: The equation that shows the enthalpy change of a chemical reaction.
Heat of combustion: The amount of heat released when one mole of a substance is completely burnt.
Standard state: The reference state for the measurement of thermodynamic quantities.
"It is a state function used in many measurements in chemical, biological, and physical systems at a constant pressure."
"The pressure–volume term expresses the work required to establish the system's physical dimensions, i.e. to make room for it by displacing its surroundings."
"The pressure-volume term is very small for solids and liquids at common conditions, and fairly small for gases. Therefore, enthalpy is a stand-in for energy in chemical systems."
"Yes, as a state function, enthalpy depends only on the final configuration of internal energy, pressure, and volume, not on the path taken to achieve it."
"The unit of measurement for enthalpy in the SI system is the joule."
"Other historical conventional units still in use include the calorie and the British thermal unit (BTU)."
"The total enthalpy of a system cannot be measured directly because the internal energy contains components that are unknown, not easily accessible, or are not of interest for the thermodynamic problem at hand."
"A change in enthalpy is the preferred expression for measurements at constant pressure, because it simplifies the description of energy transfer."
"The standard enthalpy of reaction is the enthalpy change when reactants in their standard states change to products in their standard states."
"The value can be measured by calorimetric methods even if the temperature does vary during the measurement, provided that the initial and final pressure and temperature correspond to the standard state."
"Enthalpies of chemical substances are usually listed for 1 bar (100 kPa) pressure as a standard state."
"Enthalpies and enthalpy changes for reactions vary as a function of temperature."
"Tables generally list the standard heats of formation of substances at 25 °C (298 K)."
"For endothermic processes, the change ΔH is a positive value; for exothermic processes, it is negative."
"The enthalpy of an ideal gas is independent of its pressure or volume."
"The enthalpy of an ideal gas depends only on its temperature, which correlates to its thermal energy."
"Real gases at common temperatures and pressures often closely approximate this behavior, which simplifies practical thermodynamic design and analysis."
"At constant pressure, the enthalpy change equals the energy exchanged with the environment by heat."
"Enthalpy is a stand-in for energy in chemical systems; bond, lattice, solvation, and other chemical 'energies' are actually enthalpy differences."