FACTORS AFFECTING RATE OF REACTION:
The rate of a chemical reaction measures how quickly reactants are consumed or products are formed. It depends on the conditions under which the reaction is carried out.
- Concentration: Generally, an increase in reactant concentration leads to an increase in the reaction rate. This is because a higher concentration provides more reactant particles, leading to a higher collision frequency.
- Temperature: The rate of reaction increases with the increase in temperature. In most cases, the rate of reaction becomes nearly double for 10° rise in temperature.
- Catalysts: Catalysts are substances that accelerate a reaction by providing an alternative reaction pathway with lower activation energy. They increase the rate of reaction without being consumed in the process.
Which of the following statements is false?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Rate of reaction increases with increase in time
The rate of a reaction is the change in concentration of a reactant or product per unit time. As the reaction goes on, the reactants are used up, so their concentration falls. Since the rate depends on the concentration of the reactants, the rate decreases with the passage of time; it does not increase.
Option (1) Rate of reaction increases with increase in temperature — True about the rate of reaction. The passage states that “the rate of reaction increases with the increase in temperature” and becomes nearly double for a 10° rise.
Option (2) Rate of reaction increases with increase in concentration of reactants — True about the rate of reaction. The passage states that a higher concentration gives more reactant particles and more collisions, so the rate increases.
Option (3) Rate of reaction increases in the presence of a positive catalyst — True about the rate of reaction. The passage states that a catalyst provides an alternative pathway with lower activation energy and increases the rate.
Option (4) Rate of reaction increases with increase in time — False about the rate of reaction. Time is not a factor that speeds up a reaction; as time passes the reactant concentration falls and the rate becomes slower.
NCERT (2026-27 edition):
3.2.2 Rate Expression and Rate Constant – “… rate of a reaction decreases with the passage of time as the concentration of reactants decrease. Conversely, rates generally increase when reactant concentrations increase. So, rate of a reaction depends upon the concentration of reactants.”