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Chemical Kinetics

AIPMT 2007MCQMediumNot asked in last 5 yrs+4−1
Ques. 1AIPMT 2007

The reaction of hydrogen and iodine monochloride is given as: H2(g) + 2ICl(g) 2HCl(g) + I2(g) This reaction is of first order with respect to H2(g) and ICl(g). The following mechanisms were proposed. Mechanism A: H2(g) + 2ICl(g) 2HCl(g) + I2(g) Mechanism B: H2(g) + ICl(g) HCl(g) + HI(g); slow HI(g) + ICl(g) HCl(g) + I2(g); fast Which of the above mechanism(s) can be consistent with the given information about the reaction?

  1. A and B both
  2. Neither A nor B
  3. A only
  4. B only

Answer

(4) B only

Solution

Observed rate law: Rate = k[H2][ICl] (first order in each).

Mechanism A is a single elementary step, so its rate law follows its stoichiometry:

Rate = k[H2][ICl]2 ⇒ second order in ICl, which does not agree.

Mechanism B: as per NCERT, the slowest step is the rate-determining step.

∴ Rate = k[H2][ICl] ⇒ first order in H2 and in ICl, which agrees.

Also, adding the two steps of B gives the overall reaction H2 + 2ICl 2HCl + I2.

∴ Only mechanism B is consistent.

Answer: (4)

Keep practising — Chemical Kinetics

Ques. 2AIPMT 2006

Consider the reaction : N2(g) + 3H2(g) 2NH3(g) The equality relationship between d[NH3]dt and - d[H2]dt is

  1. d[NH3]dt = - d[H2]dt
  2. d[NH3]dt = - 13 d[H2]dt
  3. + d[NH3]dt = - 23 d[H2]dt
  4. + d[NH3]dt = - 32 d[H2]dt
Ques. 3AIPMT 2006

For the reaction, 2A + B 3C + D, which of the following does not express the reaction rate?

  1. - d[A]2dt
  2. - d[C]3dt
  3. - d[B]dt
  4. d[D]dt
Ques. 4AIPMT 2005

The rate of reaction between two reactants A and B decreases by a factor of 4 if the concentration of reactant B is doubled. The order of this reaction with respect to reactant B is

  1. 2
  2. -2
  3. 1
  4. -1
Ques. 5AIPMT 2005

For a first order reaction A B the reaction rate at reactant concentration of 0.01 M is found to be 2.0 10-5 mol L-1 s-1. The half-life period of the reaction is

  1. 30 s
  2. 220 s
  3. 300 s
  4. 347 s
Ques. 6AIPMT 2004

The rate of a first order reaction is 1.5 10-2 mol L-1 min-1 at 0.5 M concentration of the reactant. The half-life of the reaction is

  1. 0.383 min
  2. 23.1 min
  3. 8.73 min
  4. 7.53 min
Ques. 7AIPMT 2003

The temperature dependence of rate constant (k) of a chemical reaction is written in terms of Arrhenius equation, k = A e-E*/RT. Activation energy (E*) of the reaction can be calculated by plotting

  1. k vs T
  2. k vs 1 T
  3. log k vs 1T
  4. log k vs 1 T
Ques. 8AIPMT 2003

If the rate of the reaction is equal to the rate constant, the order of the reaction is

  1. 0
  2. 1
  3. 2
  4. 3
Ques. 9AIPMT 2003

The reaction A B follows first order kinetics. The time taken for 0.8 mole of A to produce 0.6 mole of B is 1 hour. What is the time taken for conversion of 0.9 mole of A to produce 0.675 mole of B?

  1. 1 hour
  2. 0.5 hour
  3. 0.25 hour
  4. 2 hours
Ques. 10AIPMT 2003

The activation energy for a simple chemical reaction A B is Ea in forward direction. The activation energy for reverse reaction

  1. is negative of Ea
  2. is always less than Ea
  3. can be less than or more than Ea
  4. is always double of Ea
Ques. 11AIPMT 2003

The radioisotope, tritium (13H) has a half-life of 12.3 years. If the initial amount of tritium is 32 mg, how many milligrams of it would remain after 49.2 years?

  1. 1 mg
  2. 2 mg
  3. 4 mg
  4. 8 mg

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