Thermodynamics - Topics, Formulas, Tips, Books, FAQs
When you rub your hands for a few seconds, you will find that your palms get heated up and if you observe this phenomenon using spectacles of science, you will realize that basically mechanical energy (rubbing hands) is converted to heat energy (heated palms). Similarly, take the case of a steam engine, in which heat energy (steam) is converted into mechanical energy (movement). So basically in this chapter, you will read about different forms of energy and how one energy form is converted into another energy form.
Thermodynamics Class 11th Topics (NCERT Syllabus)
1. Introduction
Thermodynamics is the branch of physics that studies heat, temperature, and their relation with work and energy. It deals with bulk systems using macroscopic variables like pressure, volume, and temperature, without considering molecular details. Unlike mechanics, which studies motion of bodies, thermodynamics focuses on internal energy changes, such as conversion of work into heat or heat into work.
2.Thermal Equilibrium
When two bodies at different temperatures are placed in contact, heat flows from the hotter body to the colder one. This continues until both bodies attain the same temperature. At this stage, no net heat transfer occurs, and the bodies are said to be in thermal equilibrium.
3. Zeroth Law of Thermodynamics
The Zeroth Law of Thermodynamics states:
If two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.
4. Heat, Internal Energy and Work
Internal Energy (U): The total energy of all molecules in a system (kinetic + potential) due to their random motion and interactions. It depends only on the state of the system.
Heat (Q): The energy transferred because of temperature difference between the system and surroundings. It flows from hot to cold body.
Work (W): The energy transferred when a force is applied and displacement occurs (e.g., expansion or compression of a gas).
Relation (First Law form):
$
\Delta U=Q-W
$
5. First Law of Thermodynamics
The first law is the law of conservation of energy applied to a thermodynamic system. It states that: "Energy can neither be created nor destroyed, it can only change from one form to another."
In thermodynamics, the change in internal energy of a system $(\boldsymbol{\Delta} \mathbf{U})$ is equal to the heat supplied to the system (Q) minus the work done by the system (W):
$
\Delta U=Q-W
$
6. Specific Heat Capacity
The specific heat capacity (c) of a substance is the amount of heat required to raise the temperature of 1 kg of the substance by $1^{\circ} \mathrm{C}$ (or 1 K ).
$
Q=m c \Delta T
$
7. Thermodynamic State Variables and Equation of State
A thermodynamic state of a system is described by measurable state variables like pressure (P), volume (V), temperature (T), and mass.
- These variables define the macroscopic condition of the system.
- When the system changes from one state to another, these variables also change.
For an ideal gas, the relation among the state variables is given by the Equation of State:
$
P V=n R T
$
8. Thermodynamic Processes
A thermodynamic process is the way in which a system changes from one equilibrium state to another.
During the process, variables like $\mathrm{P}, \mathrm{V}$, and T may change.
The main processes are:
1. Isothermal Process - Temperature (T) remains constant.
$
P V=\mathrm{constant}
$
2. Adiabatic Process - No heat exchange ( $\mathrm{Q}=0$ ).
$
P V^\gamma=\text { constant }
$
3. Isochoric (Isovolumetric) Process - Volume (V) remains constant.
$
Q=\Delta U
$
4. Isobaric Process - Pressure (P) remains constant.
$
Q=\Delta U+W
$
9. Second Law of Thermodynamics
The Second Law of Thermodynamics tells us about the direction of natural processes.
- Kelvin-Planck Statement: It is impossible to construct a heat engine that converts all the absorbed heat into work without rejecting some heat to a sink.
- Clausius Statement: Heat cannot flow on its own from a colder body to a hotter body.
10. Carnot Engine
The Carnot engine is an ideal heat engine proposed by Sadi Carnot. It works between two temperature reservoirs and gives the maximum possible efficiency for a heat engine.
Working principle: It operates on the Carnot cycle, which consists of four reversible processes:
1. Isothermal expansion
2. Adiabatic expansion
3. Isothermal compression
4. Adiabatic compression
Efficiency of Carnot engine: $\eta=1-\frac{T_2}{T_1}$
Related topics,
Formulas for Thermodynamics
$\Delta U=\Delta Q-\Delta W$
The efficiency of heat engine, ${ }^\eta=\frac{W}{Q_1}$
The efficiency of Carnot engine, $\eta=\left(1-\frac{T_2}{T_1}\right)$
Coefficient of Performance, $\beta=\frac{T_2}{T_1-T_2}=\frac{1-\eta}{\eta}$
$
C_v=\frac{\mathrm{d} U}{\mathrm{~d} t} ; C_p=\frac{\mathrm{d} H}{\mathrm{~d} t} ; C_p-C_v=R
$
How to prepare Thermodynamics
In this chapter, you mainly have to first understand the different types of processes like the Isochoric, isobaric and adiabatic processes and you should also give a lot of attention on the P-V, P-T, V-T diagrams of these processes, many questions are asked from these diagrams itself. Most of the questions will revolve around the concept of the First law of thermodynamics so try to solve more questions from this important topic. Also, many questions will involve the ideal gas equation for solving questions, it is highly recommended to you to make a good understanding of the chapter Kinetic theory of gases. Without reading the Kinetic Theory of Gases, it would be very difficult for you to solve the questions.
Books for Thermodynamics
Recommendation for this chapter would be to first go through the NCERT book and solve questions after that you should move on to the NCERT Exemplar book for a good hold on this chapter. If you want to test yourself for competitive exams, then you shoul
d read Understanding Physics by D.C. Pandey or you could also read and practice questions from Concepts of Physics by H.C. Verma.
Thermodynamics Real Life Example
Steam Engine / Steam Turbine – Converts heat from steam into mechanical work.
Refrigerator / Air Conditioner – Uses the second law of thermodynamics to transfer heat from cold to hot regions.
Internal Combustion Engine – Burns fuel to produce heat, which does work on pistons.
Boiling Water / Kettle – Heat supplied raises the internal energy of water molecules.
Weightage of Thermodynamics in Exams
| Exam | Weightage | Remarks |
|---|---|---|
| JEE Main | Usually 1–2 questions | Concepts like the First Law, heat engines, and specific heat are commonly asked. |
| JEE Advanced | 1–2 application-based questions | may include Carnot engine, thermodynamic processes. |
| NEET (Physics) | About 2 questions | Mainly First Law, heat, and simple processes. |
NCERT Solutions Subject wise link:
- NCERT solutions for class 11 Physics.
- NCERT solutions for class 11 Chemistry.
- NCERT solutions for class 11 Mathematics.
- NCERT solutions for class 11 Biology.
NCERT Exemplar Solutions Subject wise link:
- NCERT exemplar solutions for class 11 Physics.
- NCERT exemplar solutions for class 11 Chemistry.
- NCERT exemplar solutions for class 11 Mathematics.
- NCERT exemplar solutions for class 11 Biology.
NCERT Notes Subject Wise Link: