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Standard enthalpy of combustion is the enthalpy change when one mole of an organic compound reacts with molecular oxygen (O 2) to form carbon dioxide and liquid water. For example, the standard enthalpy of combustion of ethane gas refers to the reaction C 2 H 6 (g) + (7/2) O 2 (g) → 2 CO 2 (g) + 3 H 2 O (l).
Enthalpy of atomization is the amount of enthalpy change when bonds of the compound are broken and the component atoms are separated into single atoms ( or monoatom). Enthalpy of atomization is denoted by the symbol ΔH at. The enthalpy change of atomization of gaseous H 2 O is, for example, the sum of the HO–H and H–OH bond dissociation ...
The bond dissociation energy (enthalpy) [4] is also referred to as bond disruption energy, bond energy, bond strength, or binding energy (abbreviation: BDE, BE, or D). It is defined as the standard enthalpy change of the following fission: R—X → R + X. The BDE, denoted by Dº(R—X), is usually derived by the thermochemical equation,
The term bond-dissociation energy is similar to the related notion of bond-dissociation enthalpy (or bond enthalpy), which is sometimes used interchangeably.However, some authors make the distinction that the bond-dissociation energy (D 0) refers to the enthalpy change at 0 K, while the term bond-dissociation enthalpy is used for the enthalpy change at 298 K (unambiguously denoted DH° 298).
For gas-phase reactions, ΔH⚬ values are related to bond energies to a good approximation by: ΔH⚬ = total bond energy of reactants − total bond energy of products An energy profile of an exothermic reaction. In an exothermic reaction, by definition, the enthalpy change has a negative value: ΔH = H products - H reactants < 0
The law states that the total enthalpy change during the complete course of a chemical reaction is independent of the sequence of steps taken. [2] [3] 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.e. enthalpy is a state ...
Bond cleavage is also possible by a process called heterolysis. The energy involved in this process is called bond dissociation energy (BDE). [ 2 ] BDE is defined as the " enthalpy (per mole ) required to break a given bond of some specific molecular entity by homolysis," symbolized as D . [ 3 ]
G: free energy, H: enthalpy, T: temperature, S: entropy, Δ: difference (change between original and product) Reactions can be exothermic, where ΔH is negative and energy is released. Typical examples of exothermic reactions are combustion, precipitation and crystallization, in which ordered solids are formed from disordered gaseous or liquid ...