According to collision theory, even when colliding molecules possess energy equal to or greater than the activation energy, the reaction may still not occur. The additional requirement that explains this is accounted for by:

The probability (steric) factor $P$, which accounts for proper orientation of colliding molecules

The temperature coefficient, which doubles the number of collisions

The gas constant $R$, which fixes the threshold energy

The frequency factor $A$, which lowers the activation energy

Assertion (A): For a first order reaction, the half-life is independent of the initial concentration of the reactant. Reason (R): For a first order reaction $t_{1/2} = \frac{0.693}{k}$, which contains no concentration term. Choose the correct option:

Both A and R are true and R is the correct explanation of A

Both A and R are true but R is not the correct explanation of A

The acidic hydrolysis of an ester, $CH_3COOC_2H_5 + H_2O \rightarrow CH_3COOH + C_2H_5OH$, follows first order kinetics though two reactants are involved. This is because:

Water is present in large excess, so its concentration remains nearly constant (pseudo first order)

The acid catalyst changes the true order of the reaction to zero

The ester reacts with itself and water takes no part in the reaction

The reaction is elementary with molecularity one

Chapter testChemistryIncluded in the seriesTest 8 of 27

Bihar Board Class 12 Science Chemistry · Ch 3: Chemical Kinetics

Bihar Board Class 12 Science Chemistry · Ch 3: Chemical Kinetics is an online chapter test in the Bihar Board Class 12 Science pattern, covering Chemical Kinetics. Attempt it on SeatBeat with a timer like the real exam, then see a detailed solution for every question and your score and weak-topic analysis.

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Topics in this test

Topic	Subject	Questions
Chemical Kinetics	Chemistry	30

Difficulty: 5 medium · 25 hard

Chemical Kinetics MCQ questions with answers

The first 3 of 30 questions. Unlock the series for the rest, each with a solution.

Q1. According to collision theory, even when colliding molecules possess energy equal to or greater than the activation energy, the reaction may still not occur. The additional requirement that explains this is accounted for by:
टक्कर सिद्धांत के अनुसार, जब टकराने वाले अणुओं के पास सक्रियण ऊर्जा के बराबर या उससे अधिक ऊर्जा होती है, तब भी अभिक्रिया नहीं हो सकती। इसकी व्याख्या करने वाली अतिरिक्त आवश्यकता किसके द्वारा दर्शाई जाती है:
- A. The probability (steric) factor $P$, which accounts for proper orientation of colliding molecules / प्रायिकता (त्रिविम) कारक $P$, जो टकराने वाले अणुओं के उचित अभिविन्यास को दर्शाता है
- B. The temperature coefficient, which doubles the number of collisions / ताप गुणांक, जो टक्करों की संख्या को दोगुना कर देता है
- C. The gas constant $R$, which fixes the threshold energy / गैस स्थिरांक $R$, जो देहली ऊर्जा को निश्चित करता है
- D. The frequency factor $A$, which lowers the activation energy / आवृत्ति कारक $A$, जो सक्रियण ऊर्जा को घटाता है
Solution
Besides sufficient energy, molecules must collide with the proper orientation; this is accounted for by the probability (steric) factor $P$ in the rate expression.
पर्याप्त ऊर्जा के अतिरिक्त, अणुओं को उचित अभिविन्यास के साथ टकराना चाहिए; इसे वेग व्यंजक में प्रायिकता (त्रिविम) कारक $P$ द्वारा दर्शाया जाता है।
Q2. Assertion (A): For a first order reaction, the half-life is independent of the initial concentration of the reactant. Reason (R): For a first order reaction $t_{1/2} = \frac{0.693}{k}$, which contains no concentration term. Choose the correct option:
अभिकथन (A): प्रथम कोटि की अभिक्रिया के लिए अर्ध-आयु अभिकारक की प्रारंभिक सांद्रता से स्वतंत्र होती है। कारण (R): प्रथम कोटि की अभिक्रिया के लिए $t_{1/2} = \frac{0.693}{k}$, जिसमें कोई सांद्रता पद नहीं होता। सही विकल्प चुनिए:
- A. A is true but R is false / A सत्य है परंतु R असत्य है
- B. Both A and R are true and R is the correct explanation of A / A और R दोनों सत्य हैं तथा R, A की सही व्याख्या है
- C. Both A and R are true but R is not the correct explanation of A / A और R दोनों सत्य हैं परंतु R, A की सही व्याख्या नहीं है
- D. A is false but R is true / A असत्य है परंतु R सत्य है
Solution
Since $t_{1/2} = 0.693/k$ has no concentration term, the half-life does not depend on initial concentration; R correctly explains A.
चूँकि $t_{1/2} = 0.693/k$ में कोई सांद्रता पद नहीं है, अर्ध-आयु प्रारंभिक सांद्रता पर निर्भर नहीं करती; R, A की सही व्याख्या करता है।
Q3. The acidic hydrolysis of an ester, $CH_3COOC_2H_5 + H_2O \rightarrow CH_3COOH + C_2H_5OH$, follows first order kinetics though two reactants are involved. This is because:
किसी एस्टर का अम्लीय जल-अपघटन, $CH_3COOC_2H_5 + H_2O \rightarrow CH_3COOH + C_2H_5OH$, दो अभिकारकों के शामिल होने के बावजूद प्रथम कोटि गतिकी का पालन करता है। इसका कारण है:
- A. The acid catalyst changes the true order of the reaction to zero / अम्ल उत्प्रेरक अभिक्रिया की वास्तविक कोटि को शून्य में बदल देता है
- B. The ester reacts with itself and water takes no part in the reaction / एस्टर स्वयं से अभिक्रिया करता है और जल अभिक्रिया में भाग नहीं लेता
- C. The reaction is elementary with molecularity one / अभिक्रिया प्रारंभिक है जिसकी आण्विकता एक है
- D. Water is present in large excess, so its concentration remains nearly constant (pseudo first order) / जल अत्यधिक आधिक्य में उपस्थित है, अतः इसकी सांद्रता लगभग स्थिर रहती है (छद्म प्रथम कोटि)
Solution
Water is present in large excess so its concentration stays practically constant; the reaction is truly second order but behaves as first order, i.e. a pseudo first order reaction.
जल अत्यधिक आधिक्य में उपस्थित होता है अतः इसकी सांद्रता व्यावहारिक रूप से स्थिर रहती है; अभिक्रिया वास्तव में द्वितीय कोटि की है परंतु प्रथम कोटि की भाँति व्यवहार करती है, अर्थात् एक छद्म प्रथम कोटि अभिक्रिया।

Frequently asked questions

How many questions are in the Bihar Board Class 12 Science Chemistry · Ch 3: Chemical Kinetics?

30 questions for 30 marks, to be answered in 20 minutes.

Is there negative marking in the Bihar Board Class 12 Science Chemistry · Ch 3: Chemical Kinetics?

No — wrong answers are not penalised in this test.

Which topics does the Bihar Board Class 12 Science Chemistry · Ch 3: Chemical Kinetics cover?

Chemical Kinetics (30 questions).

Is the Bihar Board Class 12 Science Chemistry · Ch 3: Chemical Kinetics free?

It is part of the BSEB Class 12 Science Test Series 2027 — Chapter-wise + Full Tests (27 tests, ₹149). You can first try Hindi · Ch 1: Chandradhar Sharma Guleri for free.

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