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51.	What happens to the rate of the reaction on increasing its temperature?(a) Rate of reaction increases(b) Rate of reaction decreases(c) Rate of reaction fluctuates between its maxima and minima(d) Rate of reaction is independent of temperatureI have been asked this question in an interview.The question is from Chemical Kinetics in division Chemical Kinetics of Chemistry – Class 12
Answer» The correct option is (a) RATE of reaction increases Easiest explanation: Increasing the temperature of a reaction results in an increase in the AVERAGE KINETIC energy of the particles taking PART in the reaction. As the kinetic energy increases, the particles MOVE faster and collide with each other more frequently and with a higher energy. This makes it easier for chemical reactions to take place. Hence, increasing the temperature increases the rate of the reaction.

52.	Which of the following explains the increase in the reaction rate by a catalyst?(a) Catalyst decreases the rate of backward reaction so that rate of forward reaction increases(b) Catalyst provides extra energy to reacting molecules so that they produce effective collisions(c) Catalyst provides an alternative path of lower activation energy to the reactants(d) Catalyst increases the number of collisions between the reacting molecules.I have been asked this question in an online interview.I would like to ask this question from Collision Theory of Chemical Reactions topic in division Chemical Kinetics of Chemistry – Class 12
Answer» CORRECT choice is (c) Catalyst provides an alternative path of lower activation ENERGY to the reactants The best explanation: It is because when the activation energy (EA) is lower in a reaction, more number of reactant particles have ENOUGH energy to react and form products. Hence, it provides an alternative path and the REACTIONS tend to occur faster.

53.	Acid hydrolysis of esters such as CH3COOC2H5 in aqueous solution is an example of a pseudo first-order reaction.(a) True(b) FalseI have been asked this question during an online interview.The doubt is from Chemical Kinetics topic in portion Chemical Kinetics of Chemistry – Class 12
Answer» The correct answer is (a) True To ELABORATE: The REACTION involved in acid HYDROLYSIS of CH3COOC2H5 in aqueous solution = CH3COOC2H5 + H2O → CH3COOH + C2H5OH. The rate LAW for the reaction is R=k[CH3COOC2H5][H2O], however, water is present in large excess and is assumed to be constant during the course of the reaction. So the rate law becomes R=k [CH3COOC2H5] and follows first order kinetics.

54.	What is the formula to calculate the time taken for the completion of a zero-order reaction?(a) t100% = [A]0/k(b) t100% = [A]0/2k(c) t100% = 2[A]0/k(d) t100% = [A]0/3kThis question was posed to me during an online exam.The above asked question is from Chemical Kinetics in division Chemical Kinetics of Chemistry – Class 12
Answer» RIGHT ANSWER is (a) t100% = [A]0/k To explain I would say: The time taken for the zero-order reaction to complete can be calculated as follows: When the reaction is complete, [A]0 = 0 Therefore, k = [A]0/t or t100% = [A]0/k.

55.	Which of the following is not similar between a first order and pseudo first order reaction?(a) The molecularity is one in both the reactions(b) Both follows first order kinetics(c) The unit of rate constant is s^-1(d) The rate of the reaction depends only on one reactantThe question was posed to me by my college professor while I was bunking the class.I'd like to ask this question from Chemical Kinetics in section Chemical Kinetics of Chemistry – Class 12
Answer» The correct choice is (a) The MOLECULARITY is one in both the reactions Explanation: Both first order and pseudo first order reactions follow first order KINETICS as in the rate of the REACTION DEPENDS only on one reactant and the unit for rate constant is s^-1 but the molecularity in first order reaction should be one where as in pseudo first order reaction the molecularity can be more than one. For example: Inversion of cane sugar.

56.	For the reaction X → Y + Z, the rate constant is 0.00058 s^-1. What percentage of X will be decomposed in 50 minutes?(a) 90.02 percent(b) 82.44 percent(c) 88.82 percent(d) 82.67 percentThe question was asked in a national level competition.My question is taken from Chemical Kinetics in portion Chemical Kinetics of Chemistry – Class 12
Answer» The correct CHOICE is (b) 82.44 percent To elaborate: Given, rate CONSTANT k= 0.00058 s^-1 Time t= 50 minutes = 50 × 60 = 3000 seconds First-order integrated rate equation, k = \(\FRAC{2.303}{t}\)log\(\frac{100}{100-a}\) log\(\frac{100}{100-a}\) = \(\frac{kt}{2.303}\) log\(\frac{100}{100-a}\) = \(\frac{0.00058 \times 3000}{2.303}\) = 0.756 a=82.44 percent.

57.	The half-life of a given reaction is doubled if the initial concentration of the reactant is doubled. What is the order of the reaction?(a) 0(b) 1(c) 2(d) 3This question was posed to me in a job interview.Asked question is from Chemical Kinetics topic in portion Chemical Kinetics of Chemistry – Class 12
Answer» The correct choice is (a) 0 The explanation: Half-life (t1⁄2) is the TIME required for a quantity to reduce to half of its initial value. The half-life of a zero-order reaction is DIRECTLY proportional to its initial CONCENTRATION. They are related as: t1/2 = [R]0/2k.

58.	What is the term used to refer to the number of collisions per unit volume of the reaction mixture?(a) Collision force(b) Collision frequency(c) Collision energy(d) Collision time periodI got this question in examination.The question is from Collision Theory of Chemical Reactions in section Chemical Kinetics of Chemistry – Class 12
Answer» Right OPTION is (b) Collision frequency For explanation: The NUMBER of collisions per unit volume of the REACTION mixture is known as collision frequency. According to this theory, the reactant molecules are assumed to be hard SPHERES and reaction is postulated to occur when molecules COLLIDE with each other.

59.	A zero-order reaction is 25% complete in 30seconds. What time does it take for 50% completion?(a) 40s(b) 70s(c) 50s(d) 60sI have been asked this question in class test.The above asked question is from Chemical Kinetics in portion Chemical Kinetics of Chemistry – Class 12
Answer» Correct ANSWER is (d) 60s The best I can EXPLAIN: T25% = (1-0.75)/K K = 0.25/30 t50% = (1 x 30)/(2 x 0.25) t50% = 15/0.25 t50% = 60s.

60.	What is the rate law for acid hydrolysis of an ester such as CH3COOC2H5 in aqueous solution?(a) k [CH3COOC2H5](b) k [CH3COOC2H5] [H2O](c) k [CH3COOC2H5]^2(d) kThe question was asked in examination.I'd like to ask this question from Rate of a Chemical Reaction topic in portion Chemical Kinetics of Chemistry – Class 12
Answer» RIGHT answer is (a) k [CH3COOC2H5] The best I can explain: Acid hydrolysis of ESTER, CH3COOC2H5 + H2O → CH3COOH + C2H5OH The order of the reaction may be altered sometimes by taking reactant in excess COMPARED to the other. The rate law R= k [CH3COOC2H5] [H2O] however water is PRESENT in excess. So, R= k [CH3COOC2H5].

61.	For the reaction C2H5COOC2H5 + H2O → C2H5COOH + C2H5OH, find the concentration of [C2H5COOC2H5] if the rate constant k=0.2 and the rate of the reaction is 0.39 s^-1.(a) 2.87 M(b) 2.01 M(c) 1.99 M(d) 1.95 MI had been asked this question in final exam.This intriguing question originated from Chemical Kinetics topic in chapter Chemical Kinetics of Chemistry – Class 12
Answer» Right option is (d) 1.95 M Explanation: The REACTION C2H5COOC2H5 + H2O → C2H5COOH + C2H5OH is a pseudo first order reaction and follows first order kinetics with rate law R=k[C2H5COOC2H5]. GIVEN, rate of the reaction R=0.39 s^-1 and rate CONSTANT k=0.2 So, 0.39 = 0.2 × [C2H5COOC2H5] [C2H5COOC2H5]=1.95 M.

62.	The rate law for inversion of cane sugar is R=k [C12H22O11][H2O]. Find the concentration of sucrose if the rate of the reaction is 0.032 s^-1 and rate constant k=0.005.(a) 5.8 M(b) 6 M(c) 6.2 M(d) 6.4 MI have been asked this question at a job interview.I need to ask this question from Chemical Kinetics in section Chemical Kinetics of Chemistry – Class 12
Answer» The correct answer is (d) 6.4 M Easiest explanation: Given, rate constant k=0.005, rate of the reaction R=0.032 s^-1. Inversion of cane SUGAR is a pseudo FIRST order reaction and water is present in large excess so the rate law BECOMES R=k [C12H22O11] 0.032= 0.005 [C12H22O11] [C12H22O11]=6.4 M.

63.	Which of the following reactions is an example of a pseudo first-order reaction?(a) H2 + Br2 → 2HBr(b) CH3CHO → CH4 + CO(c) C12H22O11 + H2O → glucose + fructose(d) PCl5 → PCl3 + Cl2I got this question in an interview.My query is from Chemical Kinetics in portion Chemical Kinetics of Chemistry – Class 12
Answer» The correct answer is (C) C12H22O11 + H2O → glucose + fructose Explanation: The order of the reaction MAY be sometimes altered sometimes by changing the conditions, for example, taking one or more reactants in excess compared to the other. The MOLECULARITY of inversion of cane sugar is 2 but follows first order kinetics because water is present in excess.

64.	What happens to the value of ΔG of a reaction when a catalyst is added to it?(a) It increases(b) It decreases(c) It remains unchanged(d) It is undefined on adding a catalystI got this question in a national level competition.The origin of the question is Chemical Kinetics topic in division Chemical Kinetics of Chemistry – Class 12
Answer» Correct ANSWER is (c) It remains unchanged Easy EXPLANATION: Gibbs free energy(ΔG) is a state FUNCTION, that is, it does not depend on the path taken by the reaction to reach the end product. It only DEPENDS on the enthalpy and the entropy of the reaction which in turn depend on the products and reactants of the reaction. Since a catalyst only changes the pathway taken by the reaction, it does not ALTER the value of ΔG.