Enthalpies for Different types of Reactions

0
34
11th Chemistry NCERT notes

Standard enthalpy of combustion (symbol: ∆c H)

It is the Enthalpy change taking place when one mole of a compound undergoes complete combustion in the presence of oxygen (∆Hc).

∆Hc because process of combustion is exothermic.

Enthalpy of atomization (symbol: ∆aH)

It is the enthalpy change occurring when one mole of the molecule breaks into its atoms.

Enthalpy of Formation (∆Hf)

It is heat change when one mole of compound is obtained from its constituent elements.

Enthalpy of formation at standard state is known as standard enthalpy of formation ∆fHo and taken as zero by convention. It also gives the idea of stability.

Bond Enthalpy (symbol: ∆bondH)

Chemical reactions involve the breaking and making of chemical bonds. Energy is required to break a bond and energy is released when a bond is formed. It is possible to relate heat of reaction to changes in energy associated with breaking and making of chemical bonds. With reference to the enthalpy changes associated with chemical bonds, two different terms are used in thermodynamics.

  1. Bond dissociation enthalpy

The energy required to break the particular bond in a gaseous molecule is called bond dissociation enthalpy. It definite in quantity and expressed in kJ mol-1.

In diatomic molecule, bond dissociation enthalpy = Bond enthalpy

In polyatomic molecule, bond dissociation enthalpy ≠ Bond enthalpy

  1. Mean bond enthalpy

Enthalpy of Solution (symbol: ∆solH)

It is the Enthalpy change when one mole of a substance is dissolved in large excess of solvent, so that on further dilution no appreciable heat change occur.

Enthalpy of Transition

It is the enthalpy change when one mole of the substance undergoes transition from one allotropic form to another.

Enthalpy of Atomisation

It is the enthalpy change occurring when one mole of the molecule breaks into its atoms.

Enthalpy of Dilution

It is the enthalpy change when one mole of the substance is diluted from one concentration to another.

Lattice Enthalpy

It is the enthalpy change, when one mole of an ionic compound dissociates into its ions in gaseous state.

 

LEAVE A REPLY

Please enter your comment!
Please enter your name here