Thermodynamics is a fundamental branch of Chemistry that deals with heat, work, temperature, and energy. Thermodynamics is very important in understanding physical processes in a wide range of areas, such as chemistry, engineering, and environmental science. For NEET students, an understanding of thermodynamics is necessary since it occurs regularly in the exam.
Thermodynamics has high weightage in the NEET exam. From previous years' trends, it is expected to get 3 questions (7% of the total) from this chapter in NEET 2025. Knowing important concepts and solving previous year questions can make a great difference in your ability to get good marks.
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Listed below is the most repeated questions of Thermodynamics with detailed solutions asked in NEET previous year exam.
A2(g) + 3B2(g) → 2AB3(g)
The enthalpy change is +15 kJ, then the internal energy change is:
Li, Be, B, C, N
Choose the correct answer from the options given below:
(A) qp is negative.
(B) ΔrH is positive.
(C) ΔrH is negative.
(D) qp is positive.
Choose the correct answer from the options given below:
(Assume that ΔH and ΔS do not vary with temperature)
NEET Exam Pattern Chemistry 2025
The NEET 2025 Chemistry section consists of 45 questions, which is 25% of the total paper. NEET Chemistry section is of total 180 marks.
| Section | Weightage (%) | Key Topics |
|---|---|---|
| Physical Chemistry | 30–35% | Thermodynamics, Electrochemistry, Chemical Kinetics, Equilibrium, and Solutions. |
| Inorganic Chemistry | 30–35% | Periodic Table, p-block, d-block, f-block elements, Coordination Compounds, and Chemical Bonding. |
| Organic Chemistry | 35–40% | Reaction mechanisms, Hydrocarbons, Alcohols, Phenols, Aldehydes, Ketones, Biomolecules, and Polymers. |
NEET 2025 Chemistry Chapter-Wise Weightage
| Unit | Weightage (%) | Class |
|---|---|---|
| Some Basic Concepts of Chemistry | 2–3% | Class 11 |
| Structure of Atom | 2–3% | Class 11 |
| Chemical Bonding and Molecular Structure | 5% | Class 11 |
| Thermodynamics | 5% | Class 11 |
| Equilibrium | 6% | Class 11 |
| Redox Reactions | 3% | Class 11 |
| The States of Matter | 3% | Class 11 |
| Solutions | 4% | Class 12 |
| Electrochemistry | 4–5% | Class 12 |
| Chemical Kinetics | 3% | Class 12 |
| Surface Chemistry | 2% | Class 12 |
| Classification of Elements and Periodicity | 2% | Class 11 |
| The p-Block Elements | 5% | Class 12 |
| The d- and f-Block Elements | 4% | Class 12 |
| Coordination Compounds | 5% | Class 12 |
| Haloalkanes and Haloarenes | 3% | Class 12 |
| Alcohols, Phenols, and Ethers | 4% | Class 12 |
| Aldehydes, Ketones, and Carboxylic Acids | 4–5% | Class 12 |
| Amines | 2–3% | Class 12 |
| Biomolecules | 3% | Class 12 |
| Polymers | 2% | Class 12 |
| Chemistry in Everyday Life | 2% | Class 12 |
NEET Last 10 Year Question Papers Pdf For NEET 2025 Preparation (2024 - 2017)
You can download the NEET previous year question paper pdfs with solutions from the table given below:
| NEET UG Previous Question Papers By NTA | Download PDF |
|---|---|
| NEET Question Paper 2024 | Check Here |
| NEET Question Paper 2023 | Check Here |
| NEET Question Paper 2022 | Check Here |
| NEET Question Paper 2021 | Check Here |
| NEET Question Paper 2020 | Check Here |
| NEET Question Paper 2019 | Check Here |
| NEET Question Paper 2018 | Check Here |
| NEET Question Paper 2017 | Check Here |
Difficulty Analysis Of NEET Chemistry:
| Section | Difficulty Level | Key Topics |
| Physical Chemistry | Moderate to Difficult | Chemical Kinetics, Thermodynamics, Electrochemistry, States of Matter, Surface Chemistry, Solutions |
| Organic Chemistry | Moderate | Hydrocarbons, Alcohols, Phenols and Ethers, Organic Chemistry based on Functional Groups, Biomolecules, Polymers, Chemistry in Everyday Life |
Frequently Asked Questions:-
1. What are the 1st, 2nd, and 3rd laws of thermodynamics?
Laws of Thermodynamics are fundamental physics principles, governing energy efficiency and heat transfer between systems. The book of thermodynamics is a good resource, to understand more. Listed below are the laws, usually referred to as thermodynamics laws:
First Law of Thermodynamics (Law of Energy Conservation): Energy can neither be created nor destroyed but can be transferred or transformed only. That is, the energy within a system remains unchanged. Mathematically, it's expressed as ΔU = Q - W,
where ΔU is the change in internal energy, Q is the heat input, and W is the work done by the system. The law is a key to explaining sustainability in energy systems.
Second Law of Thermodynamics (Law of Entropy): With every energy transfer, the total entropy (disorganization) of an environment and system always increases in the long term. This suggests not all energy can be converted to useful work—some is dissipated as heat. This law describes why perpetual motion machines cannot exist and is vital for creating energy-efficient technologies.
Third Law of Thermodynamics: While the temperature of a system nears absolute zero (0 Kelvin), the entropy of a perfect crystal will draw nearer to zero. This third law identifies limits on cooling methods and is one that is taught extensively in further studies of heat transfer.
You can gain greater insights into the concepts in a thermodynamics PDF that summarizes the laws of thermodynamics at length.
2. What is thermodynamics in simple terms?
Thermodynamics, it is the science of energy, heat transfer, and how they are related to matter. You can refer to the thermodynamics definition in physics or the thermodynamics definition in chemistry, to understand detailed information on this whichever is appropriate for your use. Simply put, it's all about comprehending how energy travels, transforms, and impacts the world around us—such as why your coffee gets cold (heat transfer) or why engines require fuel (energy efficiency). It's a crucial notion in sustainability because it allows us to design systems that employ energy efficiently, minimizing waste and environmental degradation. For more straightforward descriptions, a thermodynamics notes PDF may prove useful.
3. What is the basic principle of thermodynamics?
The fundamental principle of thermodynamics is energy conservation and entropy, usually explored in a thermodynamics system. In essence, thermodynamics says that energy can't be destroyed or created (First Law), but it always moves toward randomness (Second Law).This interaction between energy and entropy is what controls natural phenomena, from engine heat transfer to the gas behavior in renewable devices like solar cells or electric vehicles. In order to learn more about this principle, please refer to a textbook in thermodynamics because it has the tendency to break down the basic principles of a thermodynamics system.
4. What is the formula for thermodynamics?
Thermodynamics and basic formulas, traditionally referred to as the thermodynamics formula, relating to the laws:
First Law Formula: ΔU = Q - W
(ΔU is change in internal energy, Q is input heat, and W is system work). The equation is used as a base for determining the system energy efficiency of devices like heat pumps or engines.
Now, let's see the Second Law and Entropy: ΔS ≥ 0
(ΔS is entropy change, always ≥ zero for an isolated system). This is key to understanding entropy in sustainable energy systems.
In regular use, such as in heat transfer, we can use: Q = mcΔT
(Q is heat, m is mass, c is specific heat capacity, and ΔT is change in temperature).
These equations enable engineers to make energy-efficient and sustainable process improvements, which are extremely useful in the current environment-conscious era. For precise overview of thermodynamics formula, a thermodynamics PDF or notes PDF for thermodynamics can prove handy for instant access to these equations.
5. What is enthalpy and entropy? What is enthalpy and entropy with example?
Enthalpy (H): Consider enthalpy as the sum total of energy that a system possesses, including the energy that can be utilized to perform work, such as against pressure. It is defined as
H=U+PV,
where U is the internal energy, P is pressure, and V is volume.
More simply, enthalpy tends to report on the heat a system can release or take in during constant-pressure reaction. For instance, when wood is burned in a campfire, heat is released from the reaction—that's an exothermic process, and the enthalpy change (ΔH) is negative because the system relinquishes heat to the outside.
Entropy (S): Entropy, however, is just a term about randomness or disorder. It's a number for how scattered or disorganized the energy within a system is. The more random a system is, the larger its entropy is. An easy example is when ice turns to water. The molecules in the ice change from being compact in a solid state to having space to freely roam in a liquid state—higher entropy (ΔS>0) since the system is more disordered.
So, to answer "What is enthalpy and entropy with example?"—enthalpy is heat content (such as the heat released in a campfire), and entropy is disorder (such as ice turning into water, becoming more random). These are really key concepts in understanding how reactions occur, whether in the lab or in nature!
6. What is the H and S in Gibbs free energy?
Let's discuss Gibbs free energy—it's sort of the magic key to determining whether a reaction will occur on its own. The Gibbs free energy equation is:
G=H−TS
Here's what H and S represent in this case:
H (Enthalpy): It's the energy of the system, including the heat it can release or absorb. It's the same enthalpy we discussed already—the heat content of the system.
S (Entropy): This is the system's disorder, also the same entropy we have been discussing. The term TS (temperature times entropy) informs us of how much energy of the system is bound up in its randomness at a specific temperature.
Gibbs free energy (G) aids us in anticipating whether a reaction is spontaneous. If the change in Gibbs free energy (ΔG) is negative, the reaction occurs by itself—such as combining vinegar and baking soda to create a bubbly volcano. If ΔG is positive, the reaction will not occur without a little assistance. H and S are the star players in this equation, trading energy and chaos to determine the fate of the reaction.
7. What is the relationship between delta G, delta h, and delta s?
Enthalpy entropy and Gibbs free energy relationship. Relationship between free energy, enthalpy and entropy pdf.
Okay, let's link the dots between ΔG, ΔH, and ΔS—here's where things get most interesting! The enthalpy entropy and Gibbs free energy relationship is expressed in one tidy equation:
ΔG=ΔH−TΔS
ΔG is the Gibbs free energy change, and it informs us whether a reaction is spontaneous or not.
ΔH is the enthalpy change—essentially, the heat released or absorbed in the reaction.
ΔS is the change in entropy, or the amount the disorder of the system changes.
T is the temperature in Kelvin.
This equation is the heart of the relationship between free energy, enthalpy, and entropy. Let me break it down with a real-life example: Imagine you’re dissolving salt in water. The process is endothermic (ΔH>0) because it takes energy to break the salt crystals apart. But it also increases disorder (ΔS>0) because the salt ions spread out in the water. If the TΔS term (disorder contribution) outweighs the
ΔH term (heat absorbed),
ΔG will be negative, and the salt dissolves spontaneously.
If you’re looking for a relationship between free energy, enthalpy, and entropy pdf, this equation is what you’d find in most thermodynamics textbooks or study guides. It's a wonderful one to write down in your notes or add to a study PDF because it encapsulates how enthalpy (heat) and entropy (disorder) interact to decide whether or not a reaction will proceed. For example, in class 11 or 12, you may find this in your chemistry textbook under thermodynamics—it's a fundamental concept!
8. What is the Gibbs formula for entropy?
The enthalpy entropy Gibbs energy formula, which ties into the idea of a “Gibbs formula for entropy.”
The Enthalpy entropy Gibbs energy formula we’re working with is the Gibbs free energy equation:
G=H−TS
Or, when we talk about changes during a reaction:
ΔG=ΔH−TΔS
This is the enthalpy entropy Gibbs energy formula you’ll see in textbooks, whether in a pdf or a ppt for your class. It’s a staple in both class 11 and class 12 chemistry when you’re learning about thermodynamics. In class 11, you might start with the basics of enthalpy and entropy, and by class 12, you’re diving deeper into how they relate to Gibbs free energy and reaction spontaneity.
Now, about the “Gibbs formula for entropy”—there isn’t a specific formula called that, but we can rearrange the Gibbs equation to solve for entropy. If you know
ΔG and ΔH, you can find ΔS:
ΔS= ΔH−ΔG / T
This is super useful when you’re analyzing a reaction. For example, at equilibrium (like when water is at 100°C and boiling),
ΔG=0, so the equation becomes:
0=ΔH−TΔS⟹ΔS= ΔH /T
This is often used in class 12 to calculate entropy changes during phase transitions, like boiling or melting. You might see this in a ppt presentation your teacher uses, or in a pdf of your textbook chapter on thermodynamics.
For class 11 students, you’re probably just getting familiar with these terms, so focus on understanding what enthalpy (heat) and entropy (disorder) mean. By class 12, you’ll be using the Gibbs equation to predict whether reactions—like rusting of iron or dissolving sugar in water—will happen on their own. For practical understanding including the equation :-
ΔG=ΔH−TΔS and a few examples, like the salt-dissolving one mentioned earlier, to make it easier to understand.
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