Question

hey guys anyone have class 11 thermodynamics notes. its imp

Answer 1

Zeroth Law of Thermodynamics or Law of Thermal Equilibrium

The law states that if the two systems are in thermal equilibrium with a third system then they are also in thermal equilibrium with each other. Temperature is used here to know, the system is in thermal equilibrium or not.

First Law of Thermodynamics

Energy can neither be created nor destroyed although it can be converted from one form to the other.

Mathematically, ΔU = q + W

where, ΔU = internal energy change

q = heat added to system

W = work added to system

Modes of Transference of Energy

Heat (q)

It occurs when there is a difference of temperature between system and surroundings. It is a random form of energy and path dependent. Its units are joule or calorie.

Work (W)

If the system involves gaseous substances and there is a difference of pressure between system and surroundings. work is referred as pressure – volume work (WpV).


Heat Capacity (c) of a system is defined as the amount of heat required to raise the temperature of a system by 1° C.



Enthalpy (H)

It is the sum of internal energy and pV-energy of the system. It is a state function and extensive property. Mathematically,

H = U + pV

Like U. absolute value of H also cannot be known, ΔH is determined experimentally.

ΔH = H2 – H1

or ΣHp = ΣHR

For exothermic reaction (the reaction in which heat is evolved), ΔH = -ve whereas for endothermic reaction (the reaction in which heat is absorbed), ΔH = +ve.

Relationship between ΔH and ΔU

ΔH = ΔU + Δp Δ V

or ΔH = ΔU + Δn(g) RT

Here, Δn(g) = change in the number of gas moles.

Enthalpy or Heat of Reaction (ΔrH)

It is the change in enthalpy that accompanies a chemical reaction represented by a balanced chemical equation.

ΔrH = ΣH(p) – ΣH(R)

Enthalpy of reaction expressed at the standard state conditions is called standard enthalpy of reaction (ΔH).


Laws of Thermochemistry

1. Lavoisier Laplace Law

Th enthalpy change during a reaction is equal in magnitude to the enthalpy change in the reverse process but it is opposite in sign.

2. Hess’s Law of Constant Heat Summation

The standard enthalpy of a reaction. which takes place in several steps, is the sum of the standard enthalpIes of the intermediate reactions into which the overall reactions may be divided at the same temperature.

According to Hess’s law

ΔH = ΔH1 + ΔH2 + ΔH3

Applications of Hess’s law are

(a) In determination of beat of formation.

(b) In determination of heat of transition.

(c) In determination of heat of hydration.

(d) To calculate bond energies.

3. Trouton’s Rule

According to this law, “The ratio of enthalpy of vaporization and normal boiling point of a liquid IS approximately equal to 88 J per mol per kelvin. i.e.,

ΔHvap / T = 88 J / mol / K

4. Dulong and Petit Law

This law states “The product of specific heat and molar mass of any metallic element is equal to 6.4 cal/ mol/ °C. i.e.,

5. kirchhoff’s Equation

ΔCp = ΔH2 – ΔH1 / T2 – T1

and ΔCv = ΔE2 – ΔE1 / T2 – T1

6. Clausius – Clapeyron Equation

– 2.303 log p2 / p1 = ΔHv / R (T2 – T1 / T1 T2)

where, ΔHv = molar heat of vaporisation.

Bond Enthalpy

It is the average amount of energy required to break one mole of bonds in gaseous molecules.


Entropy (S)

It is the measurement of randomness or disorder of the molecules. It is a state function and extensive property.

Units : jK-1 mol-1


Second Law of Thermodynamics


All spontaneous processes or natural change are thermodynamically irreversible without the help of an extemal work. i.e., heat cannot flow itself from a colder to hotter body.

Joule-Thomson Effect

The phenomenon of cooling of a gas when it is made to expand adiabatically from a region of high pressure to a region of extremely. low pressure is known as Joule-Thomson effect. This effect is zero when an ideal gas expands in vacuum.

[When an ideal gas undergoes expansion under adiabatic condition in vacuum, no change takes place in its internal energy, i.e., (∂E / ∂V)T = 0 where, (∂E / ∂V)T is called the Internal pressure.]


Inversion Temperature

The temperature below which a gas becomes cooler on expansion is known as the inversion temperature. It is given as

Ti = 2a / Rb

where, a and b = van der Waals’ constant


Gibbs Energy or Gibbs Free Energy

It is the energy available for a system at some conditions and by which useful work can be done. It is a state function and extensive property.

G = H – TS

Change in Gibbs energy during the process 1S given by Gibbs Helmholtz equation.

(ΔG = G2 – G1 = ΔH – TΔS)

where, ΔG = Gibbs free energy

H = enthalpy of system

TS = random energy

ΔGsystem = – TΔStotal


Third Law of Thermodynamics

This law was formulated by Nernst in 1906. According to this law, “The entropy of a perfectly crystalline substance at zero K or absolute zero is taken to be zero”. We can find absolute entropies of pure substances at different temperature.