Filter Courses

Gibbs Free Energy Charge

Gibbs Free Energy Function

Volumetric Analysis

Factor Affecting The Rate of Chemical Reaction

Normality and Normal Solution

Some Thermodynamics and Their Definitions

Primary Standard Substance

Thermodynamics Process

Application of Common-ion effects


Selection of Indicators in Acid-base Titration


Molecularity of Reaction

Faraday’s Laws of Electrolysis

Faraday’s Second Law of Electrolysis

Rate Law or Rate Equation

Chemical Kinematics

Collision Theory of Rate Reaction

The relation between Faraday and Electrochemical Equivalent

Unit of Rate Constant

Order of Reaction

Equivalent Conductance or Equivalent Conductivity

Variation of Conductance with Dilution

Electrochemical Cell

Electrode Potential

Difference Between Order And Molecularity of Reaction

Application of Electrochemical

Electrolytes and Non-electrolytes

Exchange of Energy Between System and Surrounding

Internal Energy

Arrhenius Theory of Ionization

First Law of Thermodynamics

Factors Affecting Degree of Ionization

Ostwald’s Dilution Law

Heat of Reaction

Arrhenius Concept of Acid and Base

Exothermic Reaction

Brosted-Lowry Concept as Acid and Base

Enthalpy of Reaction

Lewis Concept of Acid and Base

Third Law of Thermodynamics

Second Law of Thermodynamics

Entropy Criterion and Spontaneity


Enthalpy Change and Internal Energy

Hess’s Law Of Constant Heat summation

Common ion Effect

Solubility Product

Form of Heat of Reaction

Form of Heat of Reaction

Endothermic Reaction

Spontaneous Process

Hydrolysis of Salt

PH Scale and its Limitations

Enthalpy Change and Internal Energy

Enthalpy Change and Internal Energy Photo

Enthalpy Change and Internal Energy

An enthalpy change is approximately equal to the difference between the energy used to break bonds in a chemical reaction and the energy gained by the formation of new chemical bonds in the reaction. It describes the energy change of a system at constant pressure. Enthalpy change is denoted by ΔH. At constant pressure, ΔH equals the internal energy of the system added to the pressure-volume work done by the system on its surroundings.

Internal energy is the sum of the potential energy of the system and the system’s kinetic energy. The change in internal energy (ΔU) of a reaction is equal to the heat gained or lost in a reaction when the reaction is run at constant pressure.

Relation Between  Enthalpy Change & Change in Internal Energy

For a chemical reaction, the change in enthalpy is given as:-

ΔH=  Hp   –  Hr………………………………..i)

Enthalpy is defined as
H= E + PV……………………………………ii)

At constant pressure
ΔH(Ep  +   PVp) –  (Er –P Vr)

      = Ep   + PVp –  Er   – PVr

     = (Ep   –  Er )  + (PVp  – PVr)

    =(Ep  –  Er) + P(Vp – Vr)
=ΔE + PΔV……………………iii)

Thus, the enthalpy change of a chemical reaction is the sum of internal energy change and product of pressure and volume change. At constant volume, ΔV=0. So ΔH becomes equal to ΔE.
Let us consider the gases are ideal, we have

or, PΔV = nRT
Or, ΔH –ΔE =ΔnRT  (from (iii)
or, ΔH = ΔE +ΔnRT …………………..iv)

where Δn is the change in a number of moles of gas in a gaseous chemical reaction.