Calcutta University (BSc II) Chemistry

Chemistry Gen

PART – II   [CGT 21a]

Unit II. Basic physical chemistry II

           

1.     How the rate should be expressed for the hypothetical reaction A + 3B → 2C.What are the units of "reaction rate".

     

2.     The reaction A + 2B → products has the rate law, rate = k[A][B]3. If the concentration of B is doubled while that of A is unchanged, by what factor will the rate of reaction increase?

     

3.    The reaction A + 2B → products was found to follow the rate law, rate = k[A]2[B]. Predict by what factor the rate of reaction will increase when the concentration of A is doubled, the concentration of B is tripled, and the temperature remains constant.

    

4.      Write units for a first-order rate constant.

       

5.      It takes 10.0 min for the concentration of a reactant in a first-order reaction to drop from 0.45 M to 0.32 M at 25°C. How long will it take for the reaction to be 90% complete?

       

6.      A certain first order reaction A → B is 25% complete in 42 minutes at 25°C.

What is the half-life of the reaction?

       

7.      At 700 K, the rate constant for the following reaction is 6.2 × 10-4 min-1. How many minutes are required for 20% of a sample of cyclopropane isomerize to propene?

       

8.      A first-order reaction has a rate constant of 7.5 × 10-3 /s. What is the time required for the reaction to be 60% complete.

     

9.      For the chemical reaction A → C, a plot of 1/[A]t versus time was found to give a straight line with a positive slope. What is the order of reaction?

10.  For what order reaction does the half-life get longer as the initial concentration increases?

11.  At 25°C, by what factor is the reaction rate increased by a catalyst that reduces the activation energy of the reaction by 1kJ/mol?

12.  If the Ea for the forward reaction is 25 kJ/mol and the enthalpy of reaction is -95 kJ/mol, what is Ea for the reverse reaction?

13.  According to the collision theory, all collisions do not lead to reaction. Give reason why not all collisions between reactant molecules lead to reaction?

14.  The rate constant for the first-order decomposition of C4H8 at 500°C is 9.2 × 10-3 s-1. How long will it take for 10.0% of a 0.100 M sample of C4H8 to decompose at 500°C?

15.  The oxidation of iodide ions by arsenic acid in acidic aqueous solution occurs according to the net reaction H3AsO4 + 3I- + 2 H3O+ → H3AsO3 + I3-+ H2O.

The experimental rate law for this reaction is Rate = k[H3AsO4][I-][H3O+].

What is the order of the reaction with respect to I- ?

16.  The activation energy for a certain reaction is 113 kJ/mol. By what factor (how many times) will the rate constant increase when the temperature is raised from 310 K to 325 K?