Chapter Exam

Unit 8: Chemical Kinetics — Online MCQ Test

Q: The rate constant for a first order reaction is 4.606 x 10^-3 s^-1. The time required to reduce 2.0 g of the reactant to 0.2 g is:

Answer: B. 500 s — For first order, t = (2.303 / k) * log(A0/At). t = (2.303 / 4.606e-3) * log(2.0/0.2) = 500 * log(10) = 500 s.

Q: If the half-life (t₁/₂) for a first order reaction is 1 minute, then the time required for 99.9% completion of the reaction is closest to:

Answer: D. 10 minutes — For a first order reaction, t = (2.303 / k) * log(100 / (100-99.9)) = (2.303 / k) * log(1000). Since k = 0.693 / t₁/₂ = 0.693, t = 2.303 * 3 / 0.693 ≈ 10 minutes.

Q: If the rate constant of a reaction is 0.03 s–1, how much time does it take for 7.2 mol L–1 concentration of the reactant to get reduced to 0.9 mol L–1? (Given: log 2 = 0.301)

Answer: A. 69.3 s — First-order kinetics formula: t = (2.303/k) * log(A0/At). t = (2.303/0.03) * log(7.2/0.9) = (2.303/0.03) * log(8). log(8) = 3 * log(2) = 3 * 0.301 = 0.903. t = (2.303 * 0.903) / 0.03 ≈ 69.3 s.

Q: The addition of a catalyst during a chemical reaction alters which of the following quantities?

Answer: C. Activation energy — A catalyst provides an alternative reaction pathway with a lower activation energy, thereby increasing the rate of reaction without changing the internal energy, enthalpy, or entropy of the system.

Q: The addition of a catalyst during a chemical reaction alters which of the following quantities ?

Answer: D. Activation energy — A catalyst provides an alternative reaction pathway with a lower activation energy, thereby increasing the rate of reaction without altering thermodynamic properties like enthalpy or entropy.

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Practice Unit 8: Chemical Kinetics with a free chapter-wise online MCQ test for NEET NEET (All) CHEMISTRY. This chapter covers: Rate of a chemical reaction factors affecting the rate of reactions: concentration temperature pressure and catalyst; elementary and complex reactions order and molecularity of rea.... AI-generated questions from basic to board-exam level, with instant results and explanations.

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Unit 8: Chemical Kinetics — Important Questions & Answers (FAQ)

Frequently asked questions from NEET NEET (All) CHEMISTRY — Unit 8: Chemical Kinetics, with answers and explanations. These are sample questions; the exam has its own separate question set.

The rate constant for a first order reaction is 4.606 x 10^-3 s^-1. The time required to reduce 2.0 g of the reactant to 0.2 g is:

A. 200 s
B. 500 s ✓
C. 1000 s
D. 100 s

Answer: B. 500 s
For first order, t = (2.303 / k) * log(A0/At). t = (2.303 / 4.606e-3) * log(2.0/0.2) = 500 * log(10) = 500 s.

If the half-life (t₁/₂) for a first order reaction is 1 minute, then the time required for 99.9% completion of the reaction is closest to:

A. 2 minutes
B. 4 minutes
C. 5 minutes
D. 10 minutes ✓

Answer: D. 10 minutes
For a first order reaction, t = (2.303 / k) * log(100 / (100-99.9)) = (2.303 / k) * log(1000). Since k = 0.693 / t₁/₂ = 0.693, t = 2.303 * 3 / 0.693 ≈ 10 minutes.

If the rate constant of a reaction is 0.03 s–1, how much time does it take for 7.2 mol L–1 concentration of the reactant to get reduced to 0.9 mol L–1? (Given: log 2 = 0.301)

A. 69.3 s ✓
B. 23.1 s
C. 210 s
D. 21.0 s

Answer: A. 69.3 s
First-order kinetics formula: t = (2.303/k) * log(A0/At). t = (2.303/0.03) * log(7.2/0.9) = (2.303/0.03) * log(8). log(8) = 3 * log(2) = 3 * 0.301 = 0.903. t = (2.303 * 0.903) / 0.03 ≈ 69.3 s.

The addition of a catalyst during a chemical reaction alters which of the following quantities?

A. Internal energy
B. Enthalpy
C. Activation energy ✓
D. Entropy

Answer: C. Activation energy
A catalyst provides an alternative reaction pathway with a lower activation energy, thereby increasing the rate of reaction without changing the internal energy, enthalpy, or entropy of the system.

The addition of a catalyst during a chemical reaction alters which of the following quantities ?

A. Entropy
B. Internal energy
C. Enthalpy
D. Activation energy ✓

Answer: D. Activation energy
A catalyst provides an alternative reaction pathway with a lower activation energy, thereby increasing the rate of reaction without altering thermodynamic properties like enthalpy or entropy.