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.
The Arrhenius equation for a reaction is \( k = A\,e^{-E_a/RT} \). Match List-I with List-II.
| List-I | List-II |
|---|---|
| (A) Slope of the straight-line plot of ln k against 1/T | (I) ln A |
| (B) Intercept of the straight-line plot of ln k against 1/T | (II) Frequency factor |
| (C) The constant A | (III) Activation energy, in J mol−1 |
| (D) The term Ea | (IV) \( -\frac{E_a}{R} \) |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A-IV, B-I, C-II, D-III
Taking the natural logarithm of the Arrhenius equation gives a straight-line form, y = mx + c, with y = ln k and x = 1/T:
\( \displaystyle \ln k = -\frac{E_a}{R}\left(\frac{1}{T}\right) + \ln A \)
(A) Slope of the straight-line plot of ln k against 1/T — This matches (IV) −Ea/R. The term multiplying 1/T is the slope; it is negative, because ln k falls as 1/T rises.
(B) Intercept of the straight-line plot of ln k against 1/T — This matches (I) ln A. The constant term of the line is its intercept on the ln k axis.
(C) The constant A — This matches (II) Frequency factor. A is the Arrhenius factor, also called the frequency factor or pre-exponential factor; it is a constant for a given reaction.
(D) The term Ea — This matches (III) Activation energy, in J mol−1. Ea is the energy barrier the reactants must cross; it is measured in joules per mole.
NCERT (2026-27 edition):
3.4 Temperature Dependence of the Rate of a Reaction – “…A is the Arrhenius factor or the frequency factor. It is also called pre-exponential factor. It is a constant specific to a particular reaction. R is gas constant and Ea is activation energy measured in joules/mole (J mol–1).”
“The plot of ln k vs 1/T gives a straight line according to the equation (3.19) as shown in Fig. 3.10.” … “In Fig. 3.10, slope = – Ea/R and intercept = ln A.”
\( \displaystyle k = A\,e^{-E_a/RT} \qquad (3.18) \)
\( \displaystyle \ln k = -\frac{E_a}{RT} + \ln A \qquad (3.19) \)
Fig. 3.10: A plot between ln k and 1/T