Collision Theory
Chemical Kinetics
8
JEE Qs
8%
Hard
60
min
Master the two essential criteria for an effective collision (energy and orientation) and understand how they explain the Arrhenius equation's parameters and temperature dependence.
🧮 Key Formulas
✅ Key Points for JEE
- 1For a chemical reaction to occur, reactant molecules must collide with sufficient energy (exceeding activation energy) AND proper orientation.
- 2Collision frequency (Z) is the total number of collisions per unit volume per unit time, directly proportional to reactant concentrations and generally proportional to T^(1/2).
- 3Activation Energy (E_a) is the minimum extra energy that must be supplied to the reactants to enable them to undergo effective collisions.
- 4The steric factor (P) or probability factor accounts for the proper spatial orientation of colliding molecules, which is crucial for bond breaking and formation.
- 5Temperature primarily increases the fraction of molecules possessing energy greater than or equal to the activation energy (e^(-E_a/RT)), leading to a significant increase in the rate of effective collisions.
⚠️ Common Mistakes
- ✕Confusing activation energy with threshold energy; threshold energy is the minimum total energy required, while E_a is the extra energy above average kinetic energy.
- ✕Ignoring the steric factor and assuming all high-energy collisions lead to product formation.
- ✕Incorrectly attributing the dominant effect of temperature on reaction rate solely to an increase in collision frequency, instead of the exponential increase in the fraction of effective collisions.
- ✕Failing to connect the parameters (A and E_a) of the empirical Arrhenius equation to the theoretical concepts of collision frequency, steric factor, and energy barrier.
📝 Practice Questions
See allQ72.For the thermal decomposition of N2O5( g) at constant volume, the following table can be formed, for the reaction mentioned below. 2 N2O5( g) →2 N2O4( g) + O2( g) x = … × 10−3 atm [nearest integer] Given : Rate constant for the reaction is 4.606 × 10−2 s−1 .
Q58.For a reaction, N2O5( g) →2NO2( g) + 12 O2( g) in a constant volume container, no products were present initially. The final pressure of the system when 50% of reaction gets completed is (1) 5 times of initial pressure (2) 5/2 times of initial pressure (3) 7/2 times of initial pressure (4) 7/4 times of initial pressure
Q72. A → B The molecule A changes into its isomeric form B by following a first order kinetics at a temperature of 1000 K . If the energy barrier with respect to reactant energy for such isomeric transformation is 191.48 kJ mol−1 and the frequency factor is 1020 , the time required for 50% molecules of A to become B is _________ picoseconds (nearest integer). [R = 8.314 J K−1 mol−1]
Q55. Consider the given figure and choose the correct option : (1) Activation energy of both forward and backward (2) Activation energy of forward reaction is E1 + E2 reaction is E1 + E2 and reactant is more stable and product is less stable than reactant. than product. (3) Activation energy of backward reaction is E1 and (4) Activation energy of forward reaction is E1 + E2 product is more stable than reactant. and product is more stable than reactant.
Q54.Which of the following graphs most appropriately represents a zero order reaction ? 2025 (23 Jan Shift 2) JEE Main Previous Year Paper (1) (2) (3) (4)
Q73.Consider a complex reaction taking place in three steps with rate constants k1, k2 and k3 respectively. The overall rate constant k is given by the expression k = . If the activation energies of the three steps are √k1k3k2 60,30 and 10 kJ mol−1 respectively, then the overall energy of activation in kJmol−1 is … … . (Nearest integer)
NCERT Chapters
- Class 12 Chemistry Ch 4: Chemical Kinetics