Thermodynamics

Chemistry · Class 11

Simulation · Chemistry · Class 11

The first law: a ledger of energy

"The first law: a ledger of energy" is a free, interactive Class 11 Chemistry simulation for NEET and JEE, built on the NCERT section "Work, heat and the first law" in Thermodynamics. A gas cylinder with heat arrows and a piston: q and w enter a signed ledger and the ΔU bar moves; two different paths between the same states give different q and w but equal ΔU, and a full cycle returns ΔU = 0. NEET has asked about this idea 2 times in 10 years of papers. JEE Main asked 51 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).

From the lesson Work, heat and the first law in Thermodynamics. Change the values and watch what happens.

The first law: a ledger of energyChemistry · Class 11

What it shows

NCERT § "The Internal Energy as a State Function"

A gas cylinder with heat arrows and a piston: q and w enter a signed ledger and the ΔU bar moves; two different paths between the same states give different q and w but equal ΔU, and a full cycle returns ΔU = 0.

Controls

3 to try

  • Sliderheat q −500 to +500 J
  • Sliderwork on gas w −500 to +500 J
  • Segmentedpath A / path B / complete cycle

Try this

Make ΔU = −200 J while the gas absorbs 100 J of heat (w = −300 J); then run a cycle and show ΔU = 0 but net q ≠ 0.

Common mistake

Treating q or w as state functions; sign of work done by the gas.

In NEET

10 years of papers

Asked 2 times in 10 years of NEET.

See the past questions: First Law of Thermodynamics, Thermodynamics (chapter)

In JEE Main

42 shifts analysed

51 questions from Thermodynamics across the 42 JEE Main shifts Lumi has analysed (2017–2026).

The idea behind it

NCERT § "The Internal Energy as a State Function"

  • NCERT's sign convention: work that the surroundings do on the system counts as positive w, and work the system does on its surroundings counts as negative w.
  • Likewise q is positive when heat flows into the system and negative when heat leaves it.
  • First law: ΔU = q + w. Energy of an isolated system stays constant; energy can change form but is not created or destroyed.
  • If a gas absorbs 100 J of heat and does 300 J of work on the surroundings, ΔU = +100 + (−300) = −200 J.
  • For heat exchanged at constant volume and with no other work, w = 0 and ΔU = qᵥ.
  • Adiabatic work done on a system raises its internal energy by exactly that amount: ΔU = w_ad.
  • Heat and work are two different ways of transferring energy; neither is stored in the system.

Questions

5 answers

What does the "The first law: a ledger of energy" simulation show?
A gas cylinder with heat arrows and a piston: q and w enter a signed ledger and the ΔU bar moves; two different paths between the same states give different q and w but equal ΔU, and a full cycle returns ΔU = 0.
What mistake does the "The first law: a ledger of energy" simulation fix?
A common mistake it clears up: treating q or w as state functions; sign of work done by the gas.
Has NEET asked about this idea?
Yes. NEET has asked about this idea 2 times in 10 years of papers.
Does JEE Main ask questions from Thermodynamics?
Yes. JEE Main asked 51 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
Is this simulation free?
Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Work, heat and the first law" in Thermodynamics (Class 11 Chemistry).

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