Thermodynamics — Class 11 Chemistry NCERT Solutions (Free)

Free step-by-step NCERT solutions for Class 11 Chemistry chapter "Thermodynamics" — 4 important questions with detailed answers for CBSE board exam preparation.

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TL;DR: Free step-by-step NCERT solutions for Class 11 Chemistry chapter "Thermodynamics" — 4 important questions with detailed answers for CBSE board exam pr…

Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated Jul 23, 2026

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Key Questions Covered:

Define system, surroundings, and universe in thermodynamics. Explain the type…
State the first law of thermodynamics. Explain its significance and applicati…
Define enthalpy (H) and explain the difference between ΔU and ΔH. When is ΔH …
Calculate the enthalpy change (ΔH) for the reaction: 2H₂(g) + O₂(g) → 2H₂O(l)…

Solutions Summary:

Question	Status
Define system, surroundings, and universe in thermodynami…	✓ Solved
State the first law of thermodynamics. Explain its signif…	✓ Solved
Define enthalpy (H) and explain the difference between ΔU…	✓ Solved
Calculate the enthalpy change (ΔH) for the reaction: 2H₂(…	✓ Solved

Showing 4 of 4 questions

Q1: Define system, surroundings, and universe in thermodynamics. Explain the types of thermodynamic systems with examples.

Basic Thermodynamic Concepts: System: Definition: The part of the universe that we focus on or study. Examples: → A beaker containing water and salt dissolving → A reaction vessel in a laboratory → A battery → A combustion engine Surroundings: Definition: Everything else in the universe except the system; the environment outside the system. Examples: → Air around a beaker → The walls of a reaction vessel → Heat dissipating to the environment Universe: Definition: The combination of the system...

Q2: State the first law of thermodynamics. Explain its significance and application with a numerical example.

First Law of Thermodynamics Statement: Energy can neither be created nor destroyed; it can only be converted from one form to another. Alternative Statement: The increase in internal energy of a system equals the heat added to the system minus the work done by the system. Mathematical Expression: ΔU = Q - W Where: ΔU = Change in internal energy of the system (J or kJ) Q = Heat absorbed by the system (J or kJ) W = Work done by the system (J or kJ) Alternative forms: ΔU = Q + W' (where W' is w...

Q3: Define enthalpy (H) and explain the difference between ΔU and ΔH. When is ΔH = ΔU?

Enthalpy Definition: Enthalpy (H) is the total heat content of a system at constant pressure. It is a thermodynamic property that combines internal energy and the pressure-volume work. Mathematical Definition: H = U + PV Where: H = Enthalpy (J or kJ) U = Internal energy (J or kJ) P = Pressure (Pa or atm) V = Volume (m³ or L) PV = Pressure-volume work term For changes in enthalpy: ΔH = ΔU + Δ(PV) ΔH = ΔU + (PV)final - (PV)initial ΔH = ΔU + P(Vfinal - Vinitial) ΔH = ΔU + P × ΔV (at constant pre...

Q4: Calculate the enthalpy change (ΔH) for the reaction: 2H₂(g) + O₂(g) → 2H₂O(l) using standard enthalpies of formation given: ΔH°f[H₂O(l)] = -285.8 kJ/mol, ΔH°f[H₂(g)] = 0 kJ/mol, ΔH°f[O₂(g)] = 0 kJ/mol.

Standard Enthalpy of Formation Definition: Standard enthalpy of formation (ΔH°f) is the enthalpy change when 1 mole of a compound is formed from its constituent elements in their standard states under standard conditions (25°C, 1 atm). Convention: → Elements in their standard state have ΔH°f = 0 kJ/mol → Compounds have ΔH°f values that are tabulated → Standard state indicated by ° (degree symbol) Formula for ΔH°rxn (Enthalpy of Reaction): ΔH°rxn = Σ ΔH°f(products) - Σ ΔH°f(reactants) Where:...

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