# Thermodynamics Notes, Class 11 Chemistry | SwaVid Thermodynamics, NCERT Class 11 Chemistry: notes with key ideas, formulas, common mistakes and 3 quick checks with worked answers. Canonical: https://www.swavid.com/cbse/class-11/chemistry/chapter/thermodynamics Source: https://www.swavid.com/cbse/class-11/chemistry/chapter/thermodynamics # Thermodynamics ## Formulas and definitions ## Key ideas ## Common mistakes ## Quick checks ## Keep going ## Questions parents ask ## Class 11 Chemistry on SwaVid ### Thermodynamic terms and systems ### First law of thermodynamics ### Enthalpy and heat capacity ### Hess's law of constant heat summation ### Entropy and the second law ### Gibbs energy and spontaneity ### Next chapter ### Related chapter ### Related chapter ### All chapters SwaVid › CBSE › Class 11 › Chemistry › Thermodynamics Notes written by SwaVid from the NCERT textbook. Class 11 Chemistry, Unit 5. Key ideas, formulas and common mistakes. CBSE prints 9 marks for Unit 5, not for this chapter alone. Short answer. This chapter deals with energy changes in chemical and physical processes, governed by the laws of thermodynamics. It explains internal energy, enthalpy, entropy, and Gibbs energy to predict the spontaneity and feasibility of chemical reactions. Source: NCERT Chemistry Part I (Reprint 2026-27) , Unit 5, Thermodynamics A system is the part of the universe under study, while the rest is the surroundings. Systems can be open, closed, or isolated based on the transfer of matter and energy. State functions depend only on the current state of the system, not on the path taken. Energy can neither be created nor destroyed, only transformed from one form to another. The mathematical relation is ΔU = q + w, where q is heat absorbed and w is work done on the system. Enthalpy H is defined as U + pV, measuring heat change at constant pressure (ΔH = qp). Heat capacity relates heat transferred to temperature change, with Cp - Cv = R for an ideal gas. The total enthalpy change of a reaction is the same whether it takes place in one step or in several steps. Standard enthalpies of formation can be used to calculate standard reaction enthalpies. Entropy S is a measure of randomness or disorder of a system. The second law states that the total entropy of the universe always increases during a spontaneous process. Gibbs energy G is defined as H - TS. A process is spontaneous at constant temperature and pressure if ΔG is negative, at equilibrium if ΔG = 0, and non-spontaneous if ΔG is positive. Try each question first. Then tap it to see the answer. q = +701 J (absorbed) w = -394 J (work done by the system) ΔU = q + w = 701 J - 394 J = 307 J 307 J Identify gaseous species: products are 2 moles H₂ and 1 mole O₂; reactants have 0 moles of gas Δng = n g (products) - n g (reactants) = (2 + 1) - 0 = 3 3 ΔH = -10000 J mol⁻¹ T ΔS = 300 K × (-20.0 J K⁻¹ mol⁻¹) = -6000 J mol⁻¹ ΔG = ΔH - T ΔS = -10000 - (-6000) = -4000 J mol⁻¹ = -4.0 kJ mol⁻¹ Since ΔG 0) and work done by the system is negative (w < 0). - Including liquids and solids in the calculation of Δng . Calculate Δng only using stoichiometric coefficients of gaseous products minus gaseous reactants: Δng = ∑ ng(products) - ∑ ng(reactants). - Forgetting to convert units of ΔH and ΔS before calculating ΔG . Enthalpy changes are usually given in kJ mol⁻¹ while entropy changes are in J K⁻¹ mol⁻¹. Convert entropy to kJ K⁻¹ mol⁻¹ or enthalpy to J mol⁻¹ before applying ΔG = ΔH - T ΔS. - Assuming an exothermic reaction is always spontaneous . Spontaneity depends on ΔG, not ΔH alone. An exothermic reaction with a large negative ΔS can become non-spontaneous at higher temperatures. ## Key Links - [CBSE](https://www.swavid.com/cbse) - [Class 11](https://www.swavid.com/cbse/class-11) - [Chemistry](https://www.swavid.com/cbse/class-11/chemistry/chapters) - [Start free →](https://www.swavid.com/signup) - [All 9 chapters](https://www.swavid.com/cbse/class-11/chemistry/chapters) - [NCERT Chemistry Part I (Reprint 2026-27)](https://ncert.nic.in/textbook.php) - [Open notes](https://www.swavid.com/cbse/class-11/chemistry/chapter/equilibrium) - [Open notes](https://www.swavid.com/cbse/class-11/chemistry/chapter/some-basic-concepts-of-chemistry) - [Open notes](https://www.swavid.com/cbse/class-11/chemistry/chapter/redox-reactions) - [Class 11 Chemistry](https://www.swavid.com/cbse/class-11/chemistry/chapters) - [Start free →](https://www.swavid.com/signup)