Chemistry carries the highest scoring potential in JEE for anyone who keeps the three branches separate in revision. This set covers physical chemistry numericals, organic reaction mechanisms and named reactions, and inorganic chemistry including periodic trends, chemical bonding and coordination compounds. Organic questions show the mechanism arrow by arrow, so the reasoning transfers to reactions you have not seen before.
The rate of a chemical reaction is defined as the change in concentration of reactants or products per unit time. Which of the following is NOT a factor affecting reaction rate?
Answer: C
The color of the reaction vessel does not affect the reaction rate. Temperature, nature of reactants, concentration, pressure, and catalyst are actual factors affecting reaction rate.
Q.2Easy
The half-life of a zero-order reaction is:
Answer: B
For a zero-order reaction, t₁/₂ = [A]₀/(2k), which is directly proportional to initial concentration.
Q.3Easy
A reaction has a rate constant of k = 2.5 × 10⁻⁴ s⁻¹ at 298 K. What is the order of this reaction if the units of k are s⁻¹?
Answer: B
The units s⁻¹ or time⁻¹ indicate a first-order reaction. For first-order reactions, the rate constant has units of time⁻¹.
Q.4Easy
Which of the following statements about activation energy (Eₐ) is correct?
Answer: C
Activation energy is the minimum energy required for reactants to overcome the energy barrier and form products. It is always positive and independent of temperature.
Q.5Medium
For a first-order reaction, if the initial concentration is [A]₀ = 0.5 M and after 30 seconds it becomes 0.25 M, what is the rate constant?
Answer: A
Using ln([A]₀/[A]ₜ) = kt, ln(0.05.25) = k × 30, ln(2) = k × 30, k = 0.30693 = 0.0231 s⁻¹
Q.6Medium
The mechanism of a reaction is: Step 1: A + B → C (slow), Step 2: C + D → E + F (fast). What is the overall reaction and the rate law?
Answer: A
The overall reaction is obtained by adding all steps and canceling intermediates: A + B + D → E + F. Rate law is determined by the slow step: rate = k[A][B]
Q.7Medium
Which of the following graphs represents a first-order reaction?
Answer: B
For a first-order reaction, ln[A] = ln[A]₀ - kt, so a plot of ln[A] vs t gives a straight line with slope -k.
Q.8Medium
According to Arrhenius equation, k = Ae^(-Eₐ/RT), a catalyst increases reaction rate by:
Answer: B
A catalyst provides an alternative reaction pathway with lower activation energy, thus increasing the rate constant k without affecting A or T.
Q.9Medium
For the reaction A → B, the integrated rate law for zero-order kinetics is:
Answer: A
For zero-order reaction: d[A]/dt = -k, integrating gives [A] = [A]₀ - kt, which is a linear equation.
Q.10Medium
At 300 K, a reaction has a half-life of 10 minutes. At 310 K, the half-life becomes 5 minutes. What is the approximate value of temperature coefficient (assuming RRT ≈ 2)?
Answer: B
For a first-order reaction, if half-life decreases from 10 to 5 minutes (becomes half) with a 10 K increase, this indicates the reaction rate doubles per 10 K, giving a temperature coefficient of 2.
Q.11Medium
If a reaction is first-order with rate constant k = 0.1 min⁻¹, what fraction of the reactant remains after 5 half-lives?
Answer: A
After n half-lives, fraction remaining = (21)ⁿ. After 5 half-lives: (21)⁵ = 321.
Q.12Hard
For a reaction with mechanism: A ⇌ B (fast equilibrium), B + C → D (slow), the rate law is:
Answer: C
From fast equilibrium: K = [B]/[A], so [B] = K[A]. The slow step rate law is rate = k'[B][C] = k'K[A][C] = k[A]^(21)[C] where k combines constants.
Q.13Hard
The rate constant for a reaction increases 4 times when temperature increases from 27°C to 47°C. What is the activation energy? (R = 8.314 J mol⁻¹ K⁻¹)
In a reaction, the rate increases by a factor of 8 when [A] doubles and by a factor of 2 when [B] doubles. What is the overall order of the reaction?
Answer: C
When [A] doubles, rate increases by 8 = 2³, so order w.r.t. A = 3. When [B] doubles, rate increases by 2 = 2¹, so order w.r.t. B = 1. Overall order = 3 + 1 = 4.
Q.15Hard
For the consecutive reaction A → B → C, if the rate constants are k₁ = 0.1 s⁻¹ and k₂ = 0.05 s⁻¹, and k₁ > k₂, which statement is true?
Answer: B
Since k₁ > k₂, A converts to B faster than B converts to C, so B accumulates initially and then decreases as it slowly converts to C.
Q.16Easy
The collision theory of reaction rates explains that a reaction occurs when molecules collide with:
Answer: B
According to collision theory, collisions must have both proper spatial orientation and energy ≥ activation energy to result in a reaction.
Q.17Hard
In the Lindemann mechanism for unimolecular reactions, A* represents an activated molecule. The rate-determining step is:
Answer: B
In the Lindemann mechanism: Step 1 (fast equilibrium): A + A ⇌ A* + A, Step 2 (slow): A* → products. The slow step is rate-determining.
Q.18Hard
For a pseudo-first-order reaction where [B]₀ >> [A]₀, the rate law simplifies to first-order even though the actual order is higher. This is because:
Answer: A
When [B]₀ >> [A]₀, the concentration of B doesn't change significantly during the reaction, so it can be incorporated into the rate constant, making the reaction appear first-order in A only.
Q.19Medium
Which of the following is an example of a homogeneous catalyst?
Answer: B
A homogeneous catalyst is in the same phase as reactants. H₂SO₄ (liquid) catalyzes esterification of reactants (liquid), making it homogeneous. Others are heterogeneous catalysts.
Q.20Medium
A reaction has activation energy of 50 kJ/mol. If the temperature is increased from 300 K to 310 K, the rate constant increases by a factor of approximately (R = 8.314 J/mol·K):
Answer: B
Using Arrhenius equation: log(k₂/k₁) = (Ea/2.303R)(T₂-T₁)/(T₁T₂). With Ea = 50,000 J/mol, ΔT = 10 K, this gives log(k₂/k₁) ≈ 0.30, so k₂/k₁ ≈ 2.0
