Chemistry · Class 11 Science
Ch 8Thermodynamics — Class 11 Chemistry, concept-first.
In thermodynamics, the first and most important step in analysing any process is to draw a clear boundary around the small portion of the universe we actually want to study. The part inside this boundary is called the system; everything else — literally the rest of the universe — is called the surroundings.
Key concepts
Hover a concept to preview it and jump to its most relevant Q&A.
First Law of Thermodynamics
Imagine you have a bank account. You can deposit money into it, withdraw money from it, or leave it untouched. The total amount of money in your account changes only when money goes in or comes out.
Most relevant Q&A
- A gas enclosed in a cylinder expands irreversibly against a constant external pressure of $2\ \text{atm}$, its volume increasing from $5\ \t…Free
- A system absorbs $500\ \text{J}$ of heat from its surroundings and simultaneously does $300\ \text{J}$ of work on the surroundings by expand…Free
- State the First Law of Thermodynamics in the form $\Delta U = q + w$. Explain, according to the IUPAC sign convention, the sign taken by $q$…Preview
In previous exams
How often this chapter’s concepts have been examined — real appearance data, never estimated.
Chapter contents
The NCERT structure, section by section. Open a section to see its questions, then read the concept-first solution.
System, Surroundings and Types of System
In thermodynamics, the first and most important step in analysing any process is to draw a clear boundary around the small portion of the universe we actually want to study.
Extensive and Intensive Properties; State Functions and Path Functions
Every measurable property of a thermodynamic system can be classified along two independent axes: whether it depends on the amount of matter present, and whether its value depends on the path taken to…
The Zeroth Law of Thermodynamics and Temperature
The Zeroth Law of Thermodynamics states: if two systems, A and B, are separately found to be in thermal equilibrium with a third system, C, then A and B must also be in thermal equilibrium with each o…
Work, Heat and the First Law of Thermodynamics
Work and heat are the two ways energy can be exchanged between a system and its surroundings, and both are path functions — their values depend on exactly how a process is carried out, not merely on t…
Enthalpy: H = U + PV
Most real chemical reactions are not carried out in a sealed, constant-volume container — they take place in open flasks, beakers, and reaction vessels exposed to the essentially constant pressure of…
Enthalpy Change of a Reaction and Types of Enthalpy Change
The overall enthalpy of reaction, , of any chemical equation can be broken down into a family of precisely defined, standardized enthalpy changes, each describing one very specific type of process car…
Reference Table of Standard Enthalpy Types
Hess's Law of Constant Heat Summation
Hess's law of constant heat summation states that the total enthalpy change accompanying a chemical reaction is the same regardless of whether the reaction occurs in a single step or through any numbe…
The Born-Haber Cycle
The Born-Haber cycle, named after Max Born and Fritz Haber, is a specific and especially important application of Hess's law that breaks down the formation of an ionic solid from its constituent eleme…
The Second Law of Thermodynamics and Entropy
The First Law of Thermodynamics tells us that total energy is always conserved in any process — but it says absolutely nothing about the direction in which a process actually proceeds.
Gibbs Free Energy and Spontaneity
Applying the Second Law directly requires tracking the entropy change of both the system and its surroundings — inconvenient for everyday laboratory chemistry, where what is really wanted is a single…
Criteria for Equilibrium
Equilibrium, viewed through the lens of Gibbs free energy, is not a state in which nothing is happening — it is the specific point at which the system's free energy has reached its lowest possible val…
Summary
This chapter built up chemical thermodynamics as one continuous, logical chain. It began by carefully defining a system and its surroundings, and classifying systems as open, closed or isolated, toget…
More questions
30 Q+−Show 15 questionsHide questions15 questions
- Example 1A gas enclosed in a cylinder expands irreversibly against a constant external pressure of $2\ \text{atm}$, its volume increasing from $5\ \t…Free
- Example 2A system absorbs $500\ \text{J}$ of heat from its surroundings and simultaneously does $300\ \text{J}$ of work on the surroundings by expand…Free
- Example 3A gas is taken from state A to state B by two different paths. Along Path 1 it absorbs $400\ \text{J}$ of heat and $100\ \text{J}$ of work i…Free
- Example 4Three metal blocks A, B and C are brought into contact. Block A is found to be in thermal equilibrium with block B, and block B is separatel…Preview
- Example 5For a certain reaction carried out at constant volume and $298\ \text{K}$, $\Delta U^\circ = -100\ \text{kJ mol}^{-1}$ and the number of mol…Preview
- Example 6The standard enthalpy of combustion of methane, $\text{CH}_4(g)$, is $-890.3\ \text{kJ mol}^{-1}$. Given the standard enthalpies of formatio…Preview
- Example 7The standard enthalpy of combustion of ethane, $\text{C}_2\text{H}_6(g)$, is $-1560\ \text{kJ mol}^{-1}$. Calculate the heat released when $…Preview
- Example 8The standard enthalpy of atomization of methane, $\text{CH}_4(g) \rightarrow \text{C}(g) + 4\text{H}(g)$, is $+1665\ \text{kJ mol}^{-1}$. As…Preview
- Example 9The lattice enthalpy of $\text{NaCl}(s)$ is $+788\ \text{kJ mol}^{-1}$ and the hydration enthalpies of $\text{Na}^+(g)$ and $\text{Cl}^-(g)$…Preview
- Example 10For a certain solid $X$, the enthalpy of fusion is $12.4\ \text{kJ mol}^{-1}$ and the enthalpy of vaporization is $45.6\ \text{kJ mol}^{-1}$…Preview
- Example 11Given the following data: $\text{C}(s) + \text{O}_2(g) \rightarrow \text{CO}_2(g),\ \Delta H_1 = -393.5\ \text{kJ mol}^{-1}$; and $\text{CO}…Preview
- Example 12Given the standard enthalpies of combustion: $\text{C}(s) = -393.5\ \text{kJ mol}^{-1}$, $\text{H}_2(g) = -285.8\ \text{kJ mol}^{-1}$, and $…Preview
- Example 13Construct a Born-Haber cycle for $\text{NaCl}(s)$ and calculate its lattice enthalpy from the following data: enthalpy of sublimation of $\t…Preview
- Example 14The enthalpy of vaporization of water at its normal boiling point ($373\ \text{K}$) is $40.7\ \text{kJ mol}^{-1}$. Calculate the entropy cha…Preview
- Example 15For the synthesis of ammonia, $\text{N}_2(g) + 3\text{H}_2(g) \rightarrow 2\text{NH}_3(g)$, at $298\ \text{K}$, $\Delta H^\circ = -92.4\ \te…Preview
+−Show 15 questionsHide questions15 questions
- Q16Define open, closed and isolated systems, giving one everyday or laboratory example of each. Which type of system does a stoppered thermos f…Free
- Q17Distinguish between extensive and intensive properties, giving two examples of each. If a sample of gas is divided exactly into two equal ha…Free
- Q18State the Zeroth Law of Thermodynamics. Explain why this law, despite being numbered zero, had to be recognized as a formal law before tempe…Free
- Q19State the First Law of Thermodynamics in the form $\Delta U = q + w$. Explain, according to the IUPAC sign convention, the sign taken by $q$…Preview
- Q20Distinguish between $q_p$ (heat exchanged at constant pressure) and $q_v$ (heat exchanged at constant volume). Starting from $H = U + PV$, d…Preview
- Q21For the reaction $\text{N}_2(g) + 3\text{H}_2(g) \rightarrow 2\text{NH}_3(g)$ at $298\ \text{K}$, $\Delta U^\circ = -91.8\ \text{kJ}$. Calcu…Preview
- Q22Define the standard enthalpy of atomization of an element, and write the equation, with state symbols, for the atomization of methane and of…Preview
- Q23Define the first and second ionization enthalpies of an element, writing the equation for each in the case of magnesium. Why is the second i…Preview
- Q24Define the enthalpy of solution of an ionic compound. Write, in words, how the enthalpy of solution is related to the lattice enthalpy and t…Preview
- Q25Construct a Born-Haber cycle for $\text{MgO}(s)$ and calculate its lattice enthalpy from the following data: enthalpy of sublimation of $\te…Preview
- Q26State the Second Law of Thermodynamics in terms of entropy. Using this law, explain why heat never flows spontaneously from a colder body to…Preview
- Q27$2\ \text{mol}$ of an ideal gas expands isothermally and reversibly from $10\ \text{L}$ to $20\ \text{L}$ at a constant temperature. Calcula…Preview
- Q28Predict, with a brief reason, the sign of the entropy change ($\Delta S$) for each of the following processes: (a) melting of ice at $273\ \…Preview
- Q29The thermal decomposition of calcium carbonate, $\text{CaCO}_3(s) \rightarrow \text{CaO}(s) + \text{CO}_2(g)$, has $\Delta H^\circ = +178\ \…Preview
- Q30Explain what is meant by the 'criterion for equilibrium' in terms of Gibbs free energy. Using the relation $\Delta G = \Delta H - T\Delta S$…Preview