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.
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.402Medium
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.403Medium
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.404Medium
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.405Hard
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.406Hard
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.408Hard
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.409Easy
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.410Hard
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.411Hard
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.412Medium
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.413Medium
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
Q.414Easy
For the reaction 2NO + Cl₂ → 2NOCl, the rate law is found to be Rate = k[NO]²[Cl₂]. The order with respect to NO is:
Answer: B
The exponent of [NO] in the rate law is 2, making the reaction second order with respect to NO
Q.415Medium
In the decomposition of N₂O₅, the rate constant at 320 K is 1.7 × 10⁻⁵ s⁻¹ and at 330 K is 5.0 × 10⁻⁵ s⁻¹. The activation energy is approximately:
Answer: A
Using ln(k₂/k₁) = (Ea/R)(1/T₁ - 1/T₂): ln(5.10.7) = (Ea/8.314)(3201 - 3301), solving gives Ea ≈ 50 kJ/mol
Q.416Easy
A zero-order reaction has an initial concentration of 0.5 M and rate constant k = 0.02 M/s. The time taken for the concentration to reduce to 0.1 M is:
Answer: C
For zero-order reaction: [A]₀ - [A]ₜ = kt. So 0.5 - 0.1 = 0.02 × t, giving t = 20 s
Q.417Medium
The half-life of a first-order reaction is independent of the initial concentration. If t₁/₂ = 30 minutes for a reaction, the time for the concentration to reduce to 41th of initial value is:
Answer: C
For first-order reaction, [A]ₜ = [A]₀(21)^(t/t₁/₂). For [A]ₜ = 41[A]₀, we need (21)^(t/30) = 41, so t/30 = 2, giving t = 60 minutes
Q.418Easy
In a reaction mechanism with fast pre-equilibrium followed by slow step, which statement is correct?
Answer: A
The rate-determining step (slowest step) controls the overall reaction rate, regardless of how many fast equilibrium steps precede it
Q.419Easy
For the reaction: A + B → Products with Rate = k[A][B]², what is the overall order of reaction?
Answer: C
Overall order = sum of exponents in rate law = 1 + 2 = 3 (third order reaction)
Q.420Hard
The rate constant for a reaction at 298 K is 2 × 10⁻⁵ s⁻¹ with Ea = 80 kJ/mol. What is the frequency factor (A) if rate = Ae^(-Ea/RT)?
