Lecture

Chemical Equilibria and Reactivity

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Description

This lecture covers topics related to chemical equilibria and reactivity, including enthalpy of vaporization, fusion, sublimation, enthalpies of reaction, and standard formation. It explains the concepts through examples and calculations, such as determining enthalpies at different temperatures and evaluating standard formation enthalpies.

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Related concepts (32)

Enthalpy

Enthalpy ˈɛnθəlpi, a property of a thermodynamic system, is the sum of the system's internal energy and the product of its pressure and volume. It is a state function used in many measurements in chemical, biological, and physical systems at a constant pressure, which is conveniently provided by the large ambient atmosphere. 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.

Standard enthalpy of reaction

The standard enthalpy of reaction (denoted ) for a chemical reaction is the difference between total reactant and total product molar enthalpies, calculated for substances in their standard states. This can in turn be used to predict the total chemical bond energy liberated or bound during reaction, as long as the enthalpy of mixing is also accounted for. For a generic chemical reaction the standard enthalpy of reaction is related to the standard enthalpy of formation values of the reactants and products by the following equation: In this equation, and are the stoichiometric coefficients of each product and reactant.

Enthalpy of sublimation

In thermodynamics, the enthalpy of sublimation, or heat of sublimation, is the heat required to sublimate (change from solid to gas) one mole of a substance at a given combination of temperature and pressure, usually standard temperature and pressure (STP). It is equal to the cohesive energy of the solid. For elemental metals, it is also equal to the standard enthalpy of formation of the gaseous metal atoms. The heat of sublimation is usually expressed in kJ/mol, although the less customary kJ/kg is also encountered.

Standard enthalpy of formation

In chemistry and thermodynamics, the standard enthalpy of formation or standard heat of formation of a compound is the change of enthalpy during the formation of 1 mole of the substance from its constituent elements in their reference state, with all substances in their standard states. The standard pressure value p^⦵ = 10^5 Pa (= 100 kPa = 1 bar) is recommended by IUPAC, although prior to 1982 the value 1.00 atm (101.325 kPa) was used. There is no standard temperature. Its symbol is Δ_fH^⦵.

Hess's law

Hess's law of constant heat summation, also known simply as Hess' law, is a relationship in physical chemistry named after Germain Hess, a Swiss-born Russian chemist and physician who published it in 1840. The law states that the total enthalpy change during the complete course of a chemical reaction is independent of the sequence of steps taken. Hess's law is now understood as an expression of the fact that the enthalpy of a chemical process is independent of the path taken from the initial to the final state (i.

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