CBSE Class 11 Chemistry Chapter 6: Thermodynamics NCERT Solutions

Q: What is the main difference between thermodynamics and chemical kinetics?

Thermodynamics deals with the energy changes, feasibility, and extent of a chemical reaction, while chemical kinetics focuses on the rate or speed at which a reaction proceeds.

Q: Can you explain the three types of thermodynamic systems?

An open system exchanges both energy and matter with surroundings. A closed system exchanges only energy. An isolated system exchanges neither energy nor matter.

Q: How are enthalpy change (ΔH) and internal energy change (ΔU) related?

They are related by the equation ΔH = ΔU + Δn_g RT, where Δn_g is the change in the number of moles of gas, R is the gas constant, and T is the temperature.

Q: What characterizes an adiabatic process?

In an adiabatic process, there is no heat transfer between the system and its surroundings (q=0).

Q: What happens during the free expansion of an ideal gas under adiabatic conditions?

During free expansion of an ideal gas under adiabatic conditions, no heat is exchanged (q=0), no work is done (W=0), and the temperature remains constant (ΔT=0).

Q: Why is specific heat considered an intensive property?

Specific heat is an intensive property because it depends only on the nature of the substance, not on the amount of substance present. Therefore, changing the volume of the gas does not change its specific heat.

Reviewed by NCERT Help Editorial Team · Updated on 29 Jul 2026

NCERT Solutions PDF Class 11 PDF

This chapter delves into the fundamental principles of Thermodynamics for CBSE Class 11 Chemistry. The NCERT Solutions cover key concepts such as the definition of thermodynamics, its scope, and its limitations, particularly concerning the rates of chemical reactions. It explains different types of systems (open, closed, isolated) with clear examples and clarifies the state variables used to describe a gas, like pressure, volume, temperature, and amount, referencing the ideal gas equation. The solutions also address specific heat, thermochemical reactions, enthalpy and internal energy changes, and the conditions for adiabatic processes, including free expansion. These solutions are designed to help students grasp complex thermodynamic concepts and prepare effectively for their examinations by providing clear explanations and accurate answers to the exercise questions.

Home

Quick info

Board	CBSE
Class	Class 11
Subject	Chemistry Exemplar
Session	2026
Language	English
Type	NCERT Solutions
Chapter	Chapter 6

Chapter summary

Chapter 6 of the CBSE Class 11 Chemistry syllabus focuses on Thermodynamics. The NCERT Solutions provided here clarify the core concepts, including the scope and limitations of thermodynamics, distinguishing it from reaction kinetics. It elaborates on thermodynamic systems (open, closed, isolated) and state functions. The solutions also cover specific heat, thermochemical equations, the relationship between enthalpy and internal energy changes (ΔH and ΔU), and the characteristics of adiabatic processes like free expansion. This chapter's solutions aim to build a strong foundation in thermodynamic principles.

Learning outcomes

Understand the scope and limitations of thermodynamics in chemical reactions.
Differentiate between open, closed, and isolated thermodynamic systems.
Identify and use state variables (pressure, volume, temperature, amount) to describe a gas.
Explain the concept of specific heat and its properties.
Write and interpret thermochemical equations for combustion reactions.
Relate enthalpy change (ΔH) to internal energy change (ΔU) using the ideal gas equation.
Analyze adiabatic processes, including free expansion, and their associated conditions.

Topics covered

Paper topics

Thermodynamics Scope and Limitations
Open, Closed, and Isolated Systems
State Variables (Pressure, Volume, Temperature, Amount)
Ideal Gas Equation
Specific Heat
Thermochemical Reactions
Combustion of Butane
Enthalpy of Formation
Internal Energy Change (ΔU)
Enthalpy Change (ΔH)
Relationship between ΔH and ΔU
Adiabatic Process
Free Expansion of Ideal Gas

Important topics

Scope and Limitations of Thermodynamics
Types of Thermodynamic Systems
Relationship between ΔH and ΔU
Adiabatic Processes and Free Expansion
Thermochemical Equations

PDF preview

Read page by page below. PDF is streamed from the official NCERT website — no download button on this page.

Loading document …

Page of

Loading page …

Questions and Solutions

Multiple Choice Questions (MCQs) - Q. 1

1. Thermodynamics is not concerned about:

(a) energy changes involved in a chemical reaction

(b) the extent to which a chemical reaction proceeds

(d) the feasibility of a chemical reaction

Solution: The correct option is (c). Thermodynamics is primarily concerned with the study of energy transformations that accompany chemical and physical processes. It helps predict the feasibility and extent of a reaction by analyzing energy changes (like enthalpy and entropy) and equilibrium conditions. However, thermodynamics does not provide information about how fast a reaction occurs; that is the domain of chemical kinetics.

Multiple Choice Questions (MCQs) - Q. 2

2. Which of the following statements is correct?

(a) The presence of reacting species in a covered beaker is an example of an open system.

(b) There is an exchange of energy as well as matter between the system and the surroundings in a closed system.

(d) The presence of reactants in a thermos flask or any other closed insulated vessel is an example of a closed system.

Solution: The correct option is (c). Let's analyze each statement:

A covered beaker allows for heat exchange but prevents significant matter exchange, making it a closed system, not open.
In a closed system, only energy can be exchanged with the surroundings, not matter.
A closed vessel made of copper allows for energy exchange (copper is a conductor) but prevents matter exchange, fitting the definition of a closed system.
A thermos flask is designed to minimize heat exchange and prevent matter exchange, making it an example of an isolated system, not a closed system.

\nTherefore, statement (c) is correct.

Multiple Choice Questions (MCQs) - Q. 3

3. The state of a gas can be described by quoting the relationship between:

(a) pressure, volume, temperature

(b) temperature, amount, pressure

(d) pressure, volume, temperature, amount

Solution: The correct option is (d). The state of a gas, which is a thermodynamic system, is defined by its state variables. For a gaseous system, these variables typically include pressure (p), volume (V), temperature (T), and the amount of gas (n, usually in moles). These variables are related by an equation of state, such as the ideal gas equation:

pV = nRT

. Knowing any three of these variables allows you to determine the fourth, thus completely describing the state of the gas.

Multiple Choice Questions (MCQs) - Q. 4

4. The volume of gas is reduced to half from its original volume. The specific heat will be:

(a) reduce to half

(b) be doubled

(d) increase four times

Solution: The correct option is (c). Specific heat is an intensive property. Intensive properties are those that do not depend on the amount of substance present, such as temperature, density, or boiling point. Specific heat capacity depends only on the nature of the substance (e.g., the type of gas) and its phase, not on the volume or quantity of the gas. Therefore, reducing the volume of the gas to half will not change its specific heat; it will remain constant.

Multiple Choice Questions (MCQs) - Q. 5

5. During complete combustion of one mole of butane, 2658 kJ of heat is released. The thermochemical reaction for the above change is:

(a) $2C_4H_{10}(g) + 13O_2(g) \rightarrow 8CO_2(g) + 10H_2O(l)$ ; $\Delta_c H = -2658.0 \text{kJ mol}^{-1}$

(b) $C_4H_{10}(g) + \frac{13}{2}O_2(g) \rightarrow 4CO_2(g) + 5H_2O(l)$ ; $\Delta_cH = -1329.0 \text{kJ mol}^{-1}$

(d) $C_4H_{10}(g) + \frac{13}{2}O_2(g) \rightarrow 4CO_2(g) + 5H_2O(l); \Delta_cH = + 2658.0 \text{kJ mol}^{-1}$

Solution: The correct option is (c). The problem states that the complete combustion of *one mole* of butane (

C_4H_{10}

) releases 2658 kJ of heat. This means the enthalpy change for the reaction (

\Delta_cH

) must be negative, as heat is released (exothermic process). The balanced chemical equation for the complete combustion of one mole of butane is:

$C_4H_{10}(g) + \frac{13}{2}O_2(g) \rightarrow 4CO_2(g) + 5H_2O(l)$

\nSince 2658 kJ of heat is released per mole of butane combusted, the enthalpy change is

\Delta_cH = -2658.0 \text{ kJ mol}^{-1}

. Option (a) represents the combustion of two moles of butane. Option (b) has the correct equation but the wrong value for

\Delta_cH

. Option (d) incorrectly shows the enthalpy change as positive.

Multiple Choice Questions (MCQs) - Q. 6

6. $\Delta_f U^s$ of formation of $CH_4(g)$ at certain temperature is –393 kJ mol^-1. The value of $\Delta_f H^s$ is:

(a) zero

(b) $\lt \Delta_f U^s$

(d) equal to $\Delta_f U^s$

Solution: The correct option is (b). The question seems to have a typo, as

\Delta_f U^s

usually refers to the standard internal energy of formation, and

\Delta_f H^s

to the standard enthalpy of formation. Assuming the reaction is the formation of

CH_4(g)

from its elements in their standard states, the reaction is:

$C(graphite) + 2H_2(g) \rightarrow CH_4(g)$

\nHowever, the provided answer and calculation relate to the combustion of methane,

CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(l)

. Let's proceed with the calculation based on the provided solution's context, assuming

\Delta_f U^s

is actually

\Delta_cU

for the combustion reaction. \nFor the combustion of methane:

$CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(l)$

\nThe change in the number of moles of gaseous reactants and products (

\Delta n_g

) is calculated as:

$\Delta n_g = (\text{moles of gaseous products}) - (\text{moles of gaseous reactants})$

$\Delta n_g = (1 \text{ mole of } CO_2) - (1 \text{ mole of } CH_4 + 2 \text{ moles of } O_2)$

$\Delta n_g = 1 - (1 + 2) = 1 - 3 = -2$

\nThe relationship between enthalpy change (

\Delta H

) and internal energy change (

\Delta U

) is given by:

$\Delta H = \Delta U + \Delta n_g RT$

\nSince

\Delta n_g = -2

and R and T are positive values, the term

\Delta n_g RT

is negative.

$\Delta H = \Delta U + (-2)RT$

$\Delta H = \Delta U - 2RT$

\nThis implies that

\Delta H

is less than

\Delta U

$\Delta H \lt \Delta U$

\nTherefore, if

\Delta_f U^s

(interpreted as

\Delta U

) is –393 kJ mol^-1, then

\Delta_f H^s

(interpreted as

\Delta H

) will be less than –393 kJ mol^-1.

Multiple Choice Questions (MCQs) - Q. 7

7. In an adiabatic process, no transfer of heat takes place between system and surroundings. Choose the correct option for free expansion of an ideal gas under adiabatic condition from the following:

(a) $q = 0$ , $\Delta T \neq 0$ , $W = 0$

(b) $q \neq 0$ , $\Delta T = 0$ , $W = 0$

(d) $q = 0$ , $\Delta T < 0$ , $W \neq 0$

Solution: The correct option is (c). Let's break down the conditions for free expansion of an ideal gas under adiabatic conditions:

Adiabatic Process: By definition, in an adiabatic process, there is no heat exchange between the system and the surroundings. Therefore, the heat absorbed or released, $q$ , is zero ( $q = 0$ ).
Free Expansion: Free expansion occurs when a gas expands into a vacuum. In this process, the gas does no work on the surroundings, and no work is done on the gas. Therefore, the work done, $W$ , is zero ( $W = 0$ ).
Ideal Gas: For an ideal gas, the internal energy ( $U$ ) depends only on temperature. According to the first law of thermodynamics, $\Delta U = q + W$ . Since $q = 0$ and $W = 0$ in this case, the change in internal energy $\Delta U = 0 + 0 = 0$ . Because the internal energy of an ideal gas is solely a function of temperature, $\Delta U = 0$ implies that the temperature change ( $\Delta T$ ) is also zero ( $\Delta T = 0$ ).

\nCombining these conditions, we get

q = 0

\Delta T = 0

, and

W = 0

Common mistakes

Confusing thermodynamics with chemical kinetics (rates of reaction).
Incorrectly classifying systems as open, closed, or isolated.
Misapplying the relationship between ΔH and ΔU, especially regarding Δn_g.
Not recognizing specific heat as an intensive property.
Errors in balancing thermochemical equations or assigning the correct sign for ΔH.

Revision tips

Focus on understanding the definitions of systems and state variables.
Practice writing and interpreting thermochemical equations, paying attention to stoichiometry and ΔH signs.
Memorize the relationship between ΔH and ΔU and practice calculating Δn_g.
Review the conditions for adiabatic processes and the implications for free expansion.
Use the provided examples to solidify your understanding of each concept.

Practice MCQs

Q1. Which of the following aspects is NOT a concern of thermodynamics?

Q2. A closed vessel made of copper containing reactants is an example of which type of system?

Q3. The state of a gas is completely described by which set of variables?

Q4. What happens to the specific heat of a gas if its volume is reduced to half?

Q5. For the complete combustion of one mole of butane, 2658 kJ of heat is released. Which thermochemical equation correctly represents this?

Q6. In an adiabatic process for an ideal gas undergoing free expansion, what are the values for q, ΔT, and W?

Frequently asked questions

What is the main difference between thermodynamics and chemical kinetics?