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Exam level6 past questions

Internal Energy, Heat, and Work

Explore the concepts of internal energy, heat, and work, including their definitions, relationships, and how they change during various thermodynamic processes.

Why this shows up in the exam

NEET tests your understanding of how energy is transferred and transformed in thermodynamic systems, including calculations involving heat, work, and internal energy.

How NEET tests this

Statement analysis · 4 QsNumericalDirect recall

Learn the idea

Internal energy (U) is a state function – it depends only on the state of the system. Heat (Q) and work (W) are path functions – they depend on how the change is carried out. The key insight is the First Law: ΔU = Q – W (NCERT sign convention).

🧠 Memory hook: Think of U as the house (the destination) – you reach the same house no matter which road you take. Heat and work are the roads – different routes give different distances.

Get this one clearly and it pays off every single time it shows up in the paper. 🎯

Formulas & facts to keep ready

  • U is a state function; its change depends only on initial and final states
  • Q and W are process (path) quantities, not state functions
  • First Law of Thermodynamics: ΔU = Q – W (heat added to system is positive, work done by system is positive)
  • For an ideal gas ΔU = n Cv ΔT; Cv for a mono‑atomic gas = 3R/2
  • At constant volume W = 0, so Q = ΔU; at constant pressure W = PΔV = n R ΔT
  • Cp – Cv = R for ideal gases

How to approach it

  1. 1Read the question and note which quantities (ΔU, Q, W) are asked
  2. 2Write the First‑Law relation ΔU = Q – W using NCERT sign convention
  3. 3Identify the process (constant V, constant P, isothermal, etc.) and use the appropriate expressions: W = ∫PdV, ΔU = n Cv ΔT, Q = n Cp ΔT for constant‑pressure heating
  4. 4If the statement concerns dependence on path, recall that only ΔU is path‑independent; Q and W change with the chosen path

Worked example — watch it click

Which of the following is a FALSE statement? (a) Heat is the energy transferred into or out of a system as a result of a temperature difference between the system and its surroundings. (b) The heat added to an ideal gas during the transition from state 1 to state 2 depends only on the initial and final states, 1 and 2, and not on the path by which the gas went from one to the other. (c) When a gas goes from one state to another, the work done depends on the path followed. (d) It does not make sense to refer to "the amount of heat in a body".

  • A)Heat is the energy transferred into or out of a system as a result of a temperature difference between the system and its surroundings.
  • ✅The heat added to an ideal gas during the transition from state 1 to state 2 depends only on the initial and final states, 1 and 2, and not on the path by which the gas went from one to the other.
  • C)When a gas goes from one state to another, the work done depends on the path followed.
  • D)It does not make sense to refer to "the amount of heat in a body".

The concept behind this problem

The example asks you to spot the false claim that heat depends only on the end states; it tests the distinction that only internal energy is a state function, while heat is path‑dependent.

Step by step

  1. 1Statement (a) is TRUE - heat is energy transfer due to temperature difference.
  2. 2Statement (b) is FALSE - heat is path-dependent; only internal energy change ΔU depends solely on initial and final states.
  3. 3Statement (c) is TRUE - work ∫PdV is path-dependent.
  4. 4Statement (d) is TRUE - heat is a process quantity, not a state function, so 'amount of heat in a body' is meaningless.
  5. 5The question asks for the FALSE statement.

Watch out

Students often mistake heat for a state function and choose statement (b) as true, overlooking that only ΔU is path‑independent.

Common slip-ups that cost marks

  • •Mixing up the sign convention – NCERT takes work done by the system as positive, so ΔU = Q – W
  • •Treating heat as a state function; only ΔU is path‑independent
  • •Using Cp instead of Cv when the volume is fixed (work would be incorrectly added)

🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.

Practise it

These are real questions from past NEET papers that test this exact idea.

Question 1 of 6NEET 2007

Which of the following parameters does not characterise the thermodynamic state of matter?

Push further

More challenging

20 harder questions built from the past papers above — a step up in difficulty, with distractors designed so you can't get there by elimination. Written and checked by our reviewers, not from a real paper.

Question 1 of 20

Consider 1 mole of an ideal gas. It undergoes a cyclic process A → B → C → A. The process A → B is isobaric expansion, B → C is isochoric cooling, and C → A is isothermal compression. What is the net change in internal energy for one complete cycle?

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