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Enthalpy, Work, and Heat Flow – Class 11 Chemistry MCQs Online Test
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📘 Introduction
Understanding Enthalpy, Work, and Heat Flow is a crucial part of Chapter 6: Thermodynamics in the CBSE Class 11 Chemistry syllabus. This topic focuses on the relationship between internal energy (U), enthalpy (H), heat (q), and work (w) — essential for mastering the first law of thermodynamics. Students will learn how energy is exchanged between a system and its surroundings during chemical and physical processes, and how enthalpy change (ΔH) differs from internal energy change (ΔU) depending on pressure and volume conditions.
The MCQs provided here are designed strictly according to the NCERT guidelines, ensuring relevance for both CBSE board examinations and competitive exams like JEE and NEET. These practice questions will strengthen your conceptual clarity on exothermic and endothermic reactions, calorimetry, and PV work, while improving your problem-solving accuracy. Attempt the 30-question online test to assess your preparation level and reinforce your grasp on energy flow in thermodynamic systems.
🧪 Sample MCQs (with Answers and Explanations):
Q1. Enthalpy (H) is defined as:
A) H = U – PV B) H = U + PV C) H = q + w D) H = PV/T
✅ Answer: B
💡 Explanation: Enthalpy (H) is defined as the sum of internal energy (U) and the product of pressure and volume (PV). Thus, H = U + PV.
Q2. At constant pressure, the heat exchanged (qₚ) equals:
A) ΔU B) ΔH C) w D) ΔS
✅ Answer: B
💡 Explanation: At constant pressure, the heat absorbed or released by a system equals the change in enthalpy, qₚ = ΔH.
Q3. Which relation correctly represents the difference between Cₚ and Cᵥ for an ideal gas?
A) Cₚ + Cᵥ = R B) Cₚ – Cᵥ = R C) Cₚ × Cᵥ = R D) Cₚ / Cᵥ = R
✅ Answer: B
💡 Explanation: Mayer’s relation states that for ideal gases, Cₚ – Cᵥ = R, where R is the gas constant.
Q4. When ΔH is negative for a chemical reaction, the process is:
A) Endothermic B) Exothermic C) Adiabatic D) Isochoric
✅ Answer: B
💡 Explanation: A negative enthalpy change (ΔH < 0) indicates an exothermic process — heat is released to the surroundings.
Q5. For a chemical reaction, ΔH = ΔU + ΔnRT applies when:
A) The number of moles of gas changes
B) Reaction is at constant volume
C) Temperature is zero
D) No gases are present
✅ Answer: A
💡 Explanation: The relation ΔH = ΔU + ΔnRT holds for gaseous reactions, where ΔnRT accounts for work done due to change in gas moles.