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JEE Main Thermodynamics Revision Notes

## JEE Main Thermodynamics Revision Notes - PDF Download

### What is Thermodynamics?

Thermodynamics is a branch of Physics, which deals with the processes that involve heat transfer, work, and internal energy. Thermodynamics deals with the macroscopic states of matter.

Thermodynamics is a crucial chapter because 3-4 questions with a weightage of 12-16% are expected to come from it in the JEE Main 2020. Keep reading to get a brief of the important topics covered in Thermodynamics.

Let us first go through the basic terminologies in thermodynamics.

### Types of Systems

Open system

Closed system

Isolated system

### State Functions

Pressure

Volume

Temperature

Enthalpy

Entropy

Internal energy

### Properties of a System

Intensive Properties - Temperature, Pressure, Density, a Concentration.

Extensive Properties - Volume, Entropy, Enthalpy, Energy.

### Applications of the First Law of Thermodynamics

### Isochoric Process

A constant volume process, i.e., dW = PdV = 0. Now, according to the first law of thermodynamics, we have:

dQ = dU + dW

As, dW = 0, so dQ = dU.

### Isobaric Process

The process taking place at constant pressure is the isobaric process.

### Isothermal Process

An Isothermal process takes place at constant temperature, i.e., dU = 0, or dQ = dW.

### Cyclic Process

In this process dU = 0, or dQ = dW.

### Adiabatic process

A process in which dQ = 0, i.e., dU = - dW.

### Quasi-static Process

In this process, the change is so slow that change in any parameter like P, V, or T, is considered constant.

### Free Expansion

dW = 0, dU = constant.

### The First Law of Thermodynamics

dQ = dU + dW

dQ = heat transfer

dU = change in internal energy

dW = Work done by the system

Work done in different thermodynamic processes

Reversible Process: W = - PExtΔV

Isothermal Process: W = - 2.303 nRT V2/V1, and

W = - 2.303 nRT P2/P1

Adiabatic Process: \[\frac{ nR}{ \gamma - 1}\] |T2 - T1|

Where, Poisson’s ratio, γ = Cp/Cv

Entropy

ΔS = Qrev/T

Qrev = heat supplied (isothermally & reversibly)

ΔS = 0 (Equilibrium system)

### The Second Law of Thermodynamics

A. Carnot engine - Carnot’s reverse cycle

1. First Stroke (Isothermal Expansion)

W1 = RT1 loge [V2/V1]

2. Second Stroke (Adiabatic Expansions)

W2 = \[\frac{R}{ \gamma - 1}\] |T1 - T2|

3. Third stroke (Isothermal expansion)

W3 = RT2 loge [V3/V4]

### 4. Fourth Stroke (Adiabatic Expansions)

W4 = \[\frac{R}{ \gamma - 1}\] |T1 - T2|

Total work (W) = R[T1 - T2]loge [V2/V1]

B. Carnot Efficiency Formula is

η = - Wtotal/q2= (T1 - T2)/T2= (q1 + q2)/q2

### Third Law of Thermodynamics

G = H - TS

At constant temperature and pressure:

ΔG = ΔH - TΔS

For a reversible process: ΔG ≤ 0

For a spontaneous process: ΔG < 0

At equilibrium: ΔG = 0

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