Chemistry · Chemical Kinetics · NEET
There are five main factors. 1) Concentration of reactants (for gases, pressure). 2) Temperature. 3) A catalyst. 4) Surface area of a solid reactant. 5) Nature of the reactants (how their bonds and structure behave). For NEET, remember that only some of these also change the rate constant k. Concentration and surface area change the rate but NOT k. Temperature and a catalyst change both the rate and k.
No. Increasing concentration makes the reaction faster because there are more reactant particles in the same space, so more collisions happen per second (higher collision frequency). But the rate constant k stays the same at fixed temperature. k only changes with temperature or a catalyst. This is a very common NEET trap, so keep it clear: concentration changes rate, not k.
When you heat the reactants, the molecules move faster and collide more often. More importantly, a much larger fraction of molecules now have energy equal to or greater than the activation energy (Ea). So more collisions are successful. A useful rule from NCERT: for many reactions, the rate roughly doubles for every 10 degree Celsius rise in temperature. This is why temperature is one of the strongest factors in NEET numericals.
A catalyst lowers the activation energy by giving the reaction a new, easier path. It does NOT change enthalpy (ΔH), internal energy, or entropy, because those depend only on the starting and final states, which the catalyst does not touch. A catalyst speeds up both the forward and backward reaction equally, so it does not shift the equilibrium position. NEET loves to ask: 'What does a catalyst change?' The answer is activation energy only.
Yes, for reactions involving a solid. A powder reacts faster than a big lump of the same solid because a powder has much more exposed surface. More surface means more places where collisions can happen, so the rate goes up. Surface area changes the rate but not the rate constant k. This is why we grind solids or use fine catalysts in real reactions.
Enthalpy (ΔH), internal energy, and entropy do not change. The heat of the reaction and the position of equilibrium also stay the same. A catalyst only lowers the activation energy and provides a new pathway. So the answer NTA wants is: everything stays the same EXCEPT activation energy.
The addition of a catalyst during a chemical reaction alters which of the following quantities?
An increase in the concentration of the reactants of a reaction leads to change in:
For a certain reaction, the rate = k[A]^2[B]. When the initial concentration of A is tripled keeping the concentration of B constant, the initial rate would:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
No. Only temperature and a catalyst change k. Concentration, pressure, and surface area change the rate but leave k the same at a fixed temperature.
For many reactions the rate roughly doubles (about 2 to 3 times) for every 10 degree Celsius rise. This is a rough NCERT rule, not exact, but it is useful for NEET reasoning questions.
Yes, but mainly for reactions with gases. Increasing pressure squeezes the gas molecules closer, which is like increasing concentration, so collisions and rate go up. It has almost no effect on solids or liquids.
No. A catalyst speeds up the forward and backward reactions by the same amount. It helps equilibrium arrive faster but does not move its position or change the yield.
A powder exposes far more surface area than a solid lump of the same mass. More exposed surface gives more collision sites, so the reaction goes faster.
