Equilibrium

Chemistry · Class 11

Simulation · Chemistry · Class 11

Rolling downhill to equilibrium

"Rolling downhill to equilibrium" is a free, interactive Class 11 Chemistry simulation for NEET and JEE, built on the NCERT section "K, Q and Gibbs energy" in Equilibrium. G of the reaction mixture is plotted against extent of reaction; the minimum marks equilibrium, the slope at the current Q gives ΔG = ΔG° + RT ln Q, and K = e^(−ΔG°/RT) is read off on a log scale. NEET has asked about this idea 4 times in 10 years of papers. JEE Main asked 52 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).

From the lesson K, Q and Gibbs energy in Equilibrium. Change the values and watch what happens.

Rolling downhill to equilibriumChemistry · Class 11

What it shows

NCERT § "Relationship between Equilibrium Constant K, Reaction Quotient Q and Gibbs Energy G"

G of the reaction mixture is plotted against extent of reaction; the minimum marks equilibrium, the slope at the current Q gives ΔG = ΔG° + RT ln Q, and K = e^(−ΔG°/RT) is read off on a log scale.

Controls

3 to try

  • SliderΔG° −40 to +40 kJ/mol
  • Slidertemperature 200–1000 K
  • Dragcurrent composition along the extent axis

Try this

Set ΔG° and T so that K = 10 at 298 K (ΔG° ≈ −5.7 kJ/mol); then drag the mixture to a point where ΔG > 0 and confirm Q > K.

Common mistake

Using ΔG° in kJ with R = 8.314 J; reading ΔG° = 0 as 'no reaction' instead of K = 1.

In NEET

10 years of papers

Asked 4 times in 10 years of NEET.

See the past questions: Gibbs Free Energy, Chemical Equilibrium, Equilibrium (chapter)

In JEE Main

42 shifts analysed

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

See the past questions

The idea behind it

NCERT § "Relationship between Equilibrium Constant K, Reaction Quotient Q and Gibbs Energy G"

  • ΔG = ΔG° + RT ln Q for a reaction mixture of any composition.
  • At equilibrium ΔG = 0 and Q = K, giving ΔG° = −RT ln K = −2.303 RT log K.
  • K = e^(−ΔG°/RT); a negative ΔG° means K > 1 and a positive ΔG° means K < 1.
  • When ΔG < 0 the forward reaction proceeds (Q < K); when ΔG > 0 the reverse is favoured (Q > K).
  • Use R = 8.314 J K⁻¹ mol⁻¹ with ΔG° in J mol⁻¹, not kJ mol⁻¹.

Questions

5 answers

What does the "Rolling downhill to equilibrium" simulation show?
G of the reaction mixture is plotted against extent of reaction; the minimum marks equilibrium, the slope at the current Q gives ΔG = ΔG° + RT ln Q, and K = e^(−ΔG°/RT) is read off on a log scale.
What mistake does the "Rolling downhill to equilibrium" simulation fix?
A common mistake it clears up: using ΔG° in kJ with R = 8.314 J; reading ΔG° = 0 as 'no reaction' instead of K = 1.
Has NEET asked about this idea?
Yes. NEET has asked about this idea 4 times in 10 years of papers.
Does JEE Main ask questions from Equilibrium?
Yes. JEE Main asked 52 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 "K, Q and Gibbs energy" in Equilibrium (Class 11 Chemistry).

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