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.5Easy
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.
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Q.6Easy
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.7Easy
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.8Easy
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.9Easy
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.10Easy
A catalyst increases the rate of reaction by:
Answer: B
A catalyst works by providing an alternative mechanism with lower Ea, thus increasing reaction rate without being consumed
Q.11Easy
For a reaction with rate law Rate = k[A]⁰[B]¹, if [B] is increased 4 times while [A] remains constant, the rate increases by:
Answer: B
Since the reaction is first-order in B and zero-order in A, Rate ∝ [B]. Increasing [B] by 4 times increases Rate by 4 times
Q.12Easy
For the reaction A → B, experimental data shows: [A] vs time is a straight line. This indicates:
Answer: B
A straight line in [A] vs time plot indicates [A] = [A]₀ - kt, which is the integrated rate law for zero-order reactions
Q.13Easy
For an elementary reaction: A + A + B → Products, the rate law is:
Answer: B
For elementary reactions, the rate law is determined by the stoichiometry: Rate = k[A]²[B], as 2 A molecules and 1 B molecule participate
Q.14Easy
For the reaction 2NO + O₂ → 2NO₂, the rate law is Rate = k[NO]²[O₂]. What is the overall order of reaction?
Answer: C
Overall order = sum of exponents in rate law = 2 + 1 = 3 (third order)
Q.15Easy
Half-life of a first-order reaction is 30 minutes. What fraction of reactant remains after 90 minutes?
Answer: C
After 90 min = 3 half-lives, remaining = (21)³ = 81
Q.16Easy
Which of the following statements about collision theory is INCORRECT?
Answer: B
Not all collisions are effective; only those with proper orientation and sufficient energy lead to reaction
Q.17Easy
For a zero-order reaction, the integrated rate law is [A] = [A]₀ - kt. If [A]₀ = 0.5 M and k = 0.02 M·s⁻¹, find time when [A] = 0
Answer: C
0 = 0.5 - 0.02t; t = 0.05.02 = 25 s
Q.18Easy
Consider the mechanism: (1) A + B ⇌ C (fast equilibrium), (2) C + D → E + F (slow). Which is the rate-determining step?
Answer: B
The slowest step in a mechanism is the rate-determining step (RDS), which is step 2
Q.19Easy
Which factor does NOT affect the rate constant k of a reaction?
Answer: B
Rate constant k is independent of reactant concentration; it depends on T, nature of reactants, and catalyst
