What does a catalyst change, and what does it leave alone?
"What does a catalyst change, and what does it leave alone?" is a free, interactive Class 12 Chemistry simulation for NEET and JEE, built on the NCERT section "Effect of a catalyst" in Chemical Kinetics. An energy profile with forward and reverse barriers; adding a catalyst lowers both by the same amount, so kf and kr rise by the same factor while ΔH and K stay unchanged. NEET has asked about this idea 2 times in 10 years of papers. JEE Main asked 48 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
From the lesson Effect of a catalyst in Chemical Kinetics. Change the values and watch what happens.
What it shows
NCERT §3.4.1
An energy profile with forward and reverse barriers; adding a catalyst lowers both by the same amount, so kf and kr rise by the same factor while ΔH and K stay unchanged.
Controls
5 to try
- SliderEa(forward) 40–150 kJ mol⁻¹
- SliderΔH −60 to +60 kJ mol⁻¹
- Togglecatalyst on / off (lowers both barriers)
- Slidertemperature 280–400 K
- ReadoutsEa(rev), kf, kr, K = kf/kr
Try this
Add a catalyst that makes the forward rate 100× faster at 300 K (barrier lowered by ≈11.5 kJ mol⁻¹) and confirm K has not changed.
Common mistake
A catalyst shifts equilibrium towards products or changes ΔH.
In NEET
10 years of papers
Asked 2 times in 10 years of NEET.
See the past questions: Chemical Kinetics, Chemical Kinetics (chapter)
In JEE Main
42 shifts analysed
48 questions from Chemical Kinetics across the 42 JEE Main shifts Lumi has analysed (2017–2026).
The idea behind it
NCERT §3.4.1
- A catalyst increases the rate of a reaction and is chemically unchanged at the end. MnO₂ speeds up the decomposition of KClO₃: 2KClO₃ → 2KCl + 3O₂.
- A substance added to slow a reaction is not called a catalyst; it is an inhibitor.
- Intermediate complex theory: the catalyst takes part by forming temporary bonds with a reactant to give an intermediate complex, which then breaks up into products and releases the catalyst.
- The catalyst provides a new pathway (mechanism) with a lower activation energy, so a larger fraction of molecules can cross the barrier at the same temperature.
- A small amount of catalyst is enough to change the rate greatly.
- A catalyst does not change ΔG of the reaction. It can speed up only a reaction that is already spontaneous; it cannot make a non-spontaneous reaction happen.
- It lowers the barrier equally for forward and reverse reactions, so equilibrium is reached sooner but the equilibrium constant and the equilibrium composition do not change.
Questions
5 answers
- What does the "What does a catalyst change, and what does it leave alone?" simulation show?
- An energy profile with forward and reverse barriers; adding a catalyst lowers both by the same amount, so kf and kr rise by the same factor while ΔH and K stay unchanged.
- What mistake does the "What does a catalyst change, and what does it leave alone?" simulation fix?
- A common mistake it clears up: A catalyst shifts equilibrium towards products or changes ΔH.
- 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 Chemical Kinetics?
- Yes. JEE Main asked 48 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 "Effect of a catalyst" in Chemical Kinetics (Class 12 Chemistry).
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