Thermodynamics in NEET Physics 2025: Key Formulas, Concepts & Scoring Applications

Thermodynamics is one of the most important chapters in NEET Physics, combining theory and formulas to explain how energy flows, transforms, and behaves in physical systems. While the topic might seem abstract at first, it becomes one of the most scoring chapters with proper concept clarity and practice.

In the NEET exam, Thermodynamics questions are usually based on:

Basic laws (First and Second Law)
Understanding energy conversions
Calculations using standard formulas
Real-life setups like heat engines and refrigerators

In this blog, we’ll cover:

A quick recap of key concepts
Important thermodynamic formulas
NEET-style examples and previous year questions
Practice MCQs and strategy tips

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Thermodynamics in NEET: Weightage & Focus Areas

Thermodynamics consistently appears in 2–3 questions every year in NEET Physics. The good news? These questions are typically conceptual, formula-based, and predictable if you’re familiar with NCERT and practice books.

Key Subtopics Covered in NEET:

First Law of Thermodynamics – relation between heat, work, and internal energy
Second Law of Thermodynamics – entropy, efficiency, and spontaneity
Heat Capacity & Specific Heat – formulas, units, and use cases
Work done by gas – different processes like expansion, compression
Adiabatic & Isothermal processes – their equations and graphical understanding

Trend Insight:

NEET focuses more on conceptual clarity than on lengthy calculations. Most questions require understanding + formula application, not derivation.

Concept Recap: Laws of Thermodynamics

First Law of Thermodynamics

This law is a restatement of the conservation of energy, applied to thermodynamic systems. It states:

$boldsymbol{Delta U = q + w}$

Where:

$boldsymbol{Delta U}$ : Change in internal energy
$boldsymbol{q}$ : Heat supplied to the system
$boldsymbol{w}$ : Work done on the system

Sign Conventions:

q>0q > 0q>0: Heat added to system
w>0w > 0w>0: Work done on the system
w<0w < 0w<0: Work done by the system

Applications in Thermodynamic Processes:

Process	Condition	Key Insight
Isothermal	$boldsymbol{Delta T = 0}$	$boldsymbol{Delta U = 0}$ , so $boldsymbol{q = -w}$
Adiabatic	$boldsymbol{q = 0}$	$boldsymbol{Delta U = w}$
Isochoric	$boldsymbol{Delta V = 0}$	No work done → $boldsymbol{Delta U = q}$
Isobaric	$boldsymbol{Delta P = 0}$	$boldsymbol{q = Delta U + P Delta V}$ (Enthalpy involved)

NEET often gives situations and asks you to apply the First Law with correct signs and values.

Second Law of Thermodynamics

This law introduces entropy (S) and tells us that not all heat can be converted into work. It governs spontaneity and the limits of energy conversion.

Key Concepts:

Entropy (S): A measure of randomness or disorder
Spontaneous Process: One that increases the total entropy of the universe
Irreversible processes increase entropy, reversible ones keep it constant

Applications in Heat Engines & Refrigerators:

Device	Definition
Heat Engine	Converts heat into work; has an efficiency < 100%
Refrigerator	Uses work to transfer heat from cold to hot body
Efficiency	$boldsymbol{eta = frac{W}{Q_H} = 1 - frac{T_C}{T_H}}$
COP (Refrigerator)	$boldsymbol{text{COP} = frac{Q_L}{W}}$

NEET questions often involve identifying which device is more efficient, or applying formulas to calculate work or heat transfer.

Important Terms & Process Types

Understanding thermodynamic terms and the types of processes is essential for NEET MCQs.

Key Terms:

Internal Energy (U): Total energy due to molecular motion
Enthalpy (H): Heat content at constant pressure: H=U+PVH = U + PVH=U+PV
Entropy (S): Measure of disorder; increases in spontaneous processes

Types of Thermodynamic Processes:

Process	Condition	Key Insight
Isothermal	$boldsymbol{Delta T = 0}$	$boldsymbol{Delta U = 0}$ , so $boldsymbol{q = -w}$
Adiabatic	$boldsymbol{q = 0}$	$boldsymbol{Delta U = w}$
Isochoric	$boldsymbol{Delta V = 0}$	No work done → $boldsymbol{Delta U = q}$
Isobaric	$boldsymbol{Delta P = 0}$	$boldsymbol{q = Delta U + P Delta V}$ (Enthalpy involved)

NEET frequently tests your ability to identify the correct process and apply the right formula accordingly.

Thermodynamics Formulas You Must Remember

Below is a quick reference sheet of formulas frequently used in NEET Physics questions on Thermodynamics. These are essential for solving numerical and conceptual MCQs effectively.

Concept	Formula
First Law of Thermodynamics	$boldsymbol{Delta U = q + w}$
Work (Constant Pressure)	$boldsymbol{w = -P Delta V}$
Isothermal Process	$boldsymbol{w = nRT ln left( frac{V_f}{V_i} right)}$
Adiabatic Process (PV relation)	$boldsymbol{PV^gamma = text{constant}}$
Adiabatic Process (TV relation)	$boldsymbol{TV^{gamma - 1} = text{constant}}$
Carnot Engine Efficiency	$boldsymbol{eta = 1 - frac{T_C}{T_H}}$
Refrigerator COP	$boldsymbol{text{COP} = frac{Q_L}{W}}$

Real-World Applications of Thermodynamics in NEET Questions

NEET often presents Thermodynamics questions in real-life or practical contexts. Here are some commonly tested applications:

🔧 Heat Engines and Refrigerators

Carnot cycle questions (ideal engine with max efficiency)
Calculating work done or heat transferred
Efficiency comparison between heat engines

🧬 Human Body as a Thermodynamic System

Metabolism and energy conversion
Heat production and body temperature regulation
Calorimetry-based questions on energy consumption

⚙️ Energy Conversion Devices

Solar panels: relation between energy input and output efficiency
Internal combustion engines: fuel-to-work conversion
Thermoelectric devices

♻️ Entropy & Spontaneity-Based Questions

Whether a reaction/process is feasible based on entropy change
Reversible vs irreversible processes
Identifying natural direction of energy flow

Previous Year NEET Questions: Thermodynamics

Here are actual NEET-style questions from the last few years, along with solutions and concept explanations.

Q1. NEET 2023:
A gas undergoes isothermal expansion from volume $boldsymbol{V_i}$ to $boldsymbol{V_f}$ . The work done by the gas is:
A) $boldsymbol{P(V_f - V_i)}$
B) $boldsymbol{nRT ln left( frac{V_f}{V_i} right)}$
C) $boldsymbol{frac{3}{2}nR Delta T}$
D) Zero

Answer: B
Concept: In isothermal expansion (T constant),
$boldsymbol{w = nRT ln left( frac{V_f}{V_i} right)}$

Q2. NEET 2022:
The efficiency of a Carnot engine operating between 400 K and 300 K is:
A) 25%
B) 33%
C) 50%
D) 75%

Answer: B
Solution:
$boldsymbol{eta = 1 - frac{T_C}{T_H} = 1 - frac{300}{400} = 0.25 = 25%}$

Q3. NEET 2021:
In an adiabatic process, which of the following remains constant?
A) Temperature
B) Pressure
C) Volume
D) Heat

Answer: D
Concept: In adiabatic processes, q = 0, so no heat exchange occurs.

Q4. NEET 2020:
What is the work done by 1 mole of an ideal gas during isothermal expansion from 2L to 4L at 300K?
(R = 8.314 J/mol·K)
A) 1728 J
B) 1730 J
C) 2078 J
D) 2100 J

Solution:

$boldsymbol{w = nRT ln left( frac{V_f}{V_i} right) = 1 times 8.314 times 300 times ln(2) approx 2494.2 times 0.693 = 1729.4 text{J}}$

Answer: A

Practice Questions: Thermodynamics

Here are 5 NEET-style MCQs to test your understanding of key Thermodynamics concepts and formulas.

Q1. What is the internal energy change when 100 J of heat is added to a system that does 40 J of work?

A) 60 J
B) 140 J
C) –60 J
D) –140 J

Answer: A
Solution: $boldsymbol{Delta U = q + w = 100 + (-40) = 60 text{J}}$

Q2. A system undergoes an isochoric process absorbing 200 J of heat. What is the change in internal energy?

A) 0 J
B) 200 J
C) –200 J
D) Cannot be determined

Answer: B
Concept: In an isochoric process (ΔV = 0), w = 0, so
$boldsymbol{Delta U = q = 200 text{J}}$

Q3. Which of the following has zero work done?
A) Isobaric process
B) Isothermal process
C) Isochoric process
D) Adiabatic process

Answer: C
Explanation:
In isochoric process (constant volume),
$boldsymbol{w = -P Delta V = 0}$

Q4. Which process involves both temperature and volume change but no heat exchange?
A) Isothermal
B) Isochoric
C) Isobaric
D) Adiabatic

Answer: D
Explanation:
In adiabatic processes, $boldsymbol{q = 0}$ , but T and V change.

Q5. What is the efficiency of a Carnot engine operating between 600 K and 300 K?

A) 25%
B) 50%
C) 60%
D) 30%

Answer: B
$boldsymbol{eta = 1 - frac{T_C}{T_H} = 1 - frac{300}{600} = 0.5 = 50%}$

NEET Strategy for Thermodynamics

To score well in Thermodynamics, your focus should be on understanding concepts and applying formulas smartly rather than memorizing derivations. Here’s how to approach it:

Practice Application-Based Problems

NEET doesn’t ask for derivations but often tests how well you can apply formulas to new situations.
Prioritize questions involving work done, energy exchange, efficiency, and heat flow.
Use chapter-wise MCQ books and NEET PYQ banks to build accuracy.

Visualize with PV Diagrams

Understand how pressure-volume (PV) diagrams represent thermodynamic processes:
- Isobaric = horizontal line
- Isochoric = vertical line
- Isothermal & Adiabatic = curves
These visuals help you easily identify processes and apply the right equation.

Master Sign Conventions

Students lose marks by confusing signs. Remember:
- Work done by the system: $boldsymbol{w < 0}$
- Work done on the system: $boldsymbol{w > 0}$
- Heat added to the system: $boldsymbol{q > 0}$
- Heat lost by the system: $boldsymbol{q < 0}$

Tip: Keep a formula + sign flashcard for last-minute revision before full mock tests.

FAQs on Thermodynamics for NEET

Are derivations important for NEET Physics?

No. NEET focuses on application of formulas, not their derivation. However, understanding the logic behind the formula can help retain it better. Focus more on when and how to use it in different processes.

Is Thermodynamics the same in Physics and Chemistry NEET syllabus?

The basic concepts overlap, but the approach differs:

Physics Thermodynamics deals with energy transformations, PV work, efficiency, and gas laws.
Chemistry Thermodynamics focuses more on enthalpy, free energy, spontaneity, and equilibrium.

NEET asks questions from both domains separately, so study each context with its own scope in mind.

What’s the best way to revise this chapter quickly?

Create a formula sheet (or use the one linked in this blog).
Practice PYQs from the last 10 years – they repeat question styles.
Use chapter-wise quizzes to reinforce concepts like adiabatic vs isothermal.
Keep a mistake log of sign errors, skipped units, or process identification issues.

Check out our NEET Residential Coaching option for focused preparation.

Conclusion

Thermodynamics is a highly conceptual and formula-based chapter that appears consistently in NEET Physics. The best part? Its questions are often predictable and directly based on standard formulas and processes.

To master this chapter: