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Q1. What does the expression   signify?
 

• 1) Instantaneous rate of reaction
• 2) Average rate of reaction
• 3) Concentration of the catalyst
• 4) Order of reaction

Solution

Average rate of reaction is the rate of reaction for a fixed interval of time.

Q2. In a reaction 2A + B → A₂B, the reactant A disappears at:

• 1) The same rate at which B will disappear
• 2) The same rate at which A₂B will form
• 3) Half the rate at which B will disappear
• 4) Twice the rate at which B will disappear

Solution

According to the given equation, the rate of disappearance of reactant A is twice the rate of disappearance of reactant B.

Q3. The decomposition of N₂O₅ is first order reaction and represented by After 15 minutes the volume of O₂ produced is 9 cc and at the end of the reaction 35 cc. The rate constant is equal to

• 1)
• 2)
• 3)
• 4)

Solution

Q4. The rate law for a reaction A + H₂O → B is rate α [A]. Find the molecularity and order of the reaction.

Solution

The molecularity of the reaction is 2 and order of the reaction is 1.

Q5. What are the units for the rate constant of first order reaction?

Solution

The unit for the rate constant of first order reaction is s^-1.

Q6. What are the two conditions that are necessary for effective collisions?

Solution

The two conditions that are necessary for effective collisions are: i)    The molecules should collide with sufficient kinetic energy also called the threshold energy. ii) The molecules should have proper orientation.

Q7. Name the factors that influence the rate of a chemical reaction.

Solution

The rate of a chemical reaction is influenced by the following factors: i)       Concentration of the reactants ii)     Temperature of the reactants iii)    Nature of the reacting substances iv)   Presence of catalyst v)    Exposure to radiations

Q8. A foreign substance that increase the speed of a chemical reaction is called

• 1) moderator
• 2) catalyst
• 3) inhibitor
• 4) promotor

Solution

A catalyst is a substance whose addition to a reaction enhances the rate.

Q9. For a reaction A → B, it is found that the rate of the reaction quadruples when the concentration of A is doubled. The rate for the reaction is Rate = k [A]^x, where the value of x is:

• 1) 0
• 2) 1
• 3) 3
• 4) 2

Solution

Rate = k[A]^x When the rate of the reaction quadruples, Rate₁ = 4 Rate k[2A]^x = 4 k[A]^x [2A]^x/[A]^x = 4 so, x=2  

Q10. For the reaction 2A + B → 3C + D Which of the following does not express the reaction rate?

• 1)
• 2)
• 3)
• 4)

Solution

  For the reaction 2A + B → 3C + D, The reaction rate is written as follows: The reaction rate w.r.t. A The reaction rate w.r.t. B The reaction rate w.r.t. C The reaction rate w.r.t. D .  The products have a + sign because the concentration of the products increases with time. Hence, the answer (1) is not the correct expression to represent the rate of reaction.  

Q11. For a chemical reaction 2A + B → C, the rate of formation of C is 0.25 mol L^-1hr^-1. What is the rate of disappearance of A and B?

Solution

According to the equation, the rate of disappearance of A is twice the rate of formation of C. So rate of disappearance of A = - 0.5 mol L^-1 h^-1 and that of B is -0.25 mol L^-1hr ^-1

Q12. The instantaneous rate of reaction A  B is . What is the significance of plus and minus sign?

Solution

In the above equation the negative sign indicates the decrease in concentration of the reactant and a positive sign indicates the increase in concentration of the product.

Q13. Draw schematic graphs showing the following details of the first order reactions.i) Variation of the rate of reaction with change in the concentration of the reactant. ii) Variation of In [R] Vs t and Log [Ro]/[R] vs t.

Solution

Q14. The rate constant of a first order reaction becomes 6 times when the temperature is increased from 350 K to 410 K. Calculate the energy of activation for the reaction.(R = 8.314 JK^-1 mol^-1)

Solution

 

Q15. The rate of formation of nitric oxide (NO) in the following reaction is 3.6 x 10^-3 mol L^-1 s^-1.  4NH_{3 (g)} + 5O_{2 (g)}  4NO_{2 (g)} + 6H₂O _(g) Find the rate of disappearance of Oxygen.

Solution

The rate of above reaction in terms of Oxygen and NO are Therefore rate of disappearance of Oxygen =

Q16. The experimental data for the reaction: 2A + B₂ → 2AB is: Write the rate equation for the reaction?

Solution

When A is constant, the rate of the reaction doubles on doubling the concentration of B. i.e, Rate ∝ [Br₂]¹ When the concentration of B is constant, the rate of reaction remains same on doubling the concentration of A i.e, rate ∝ [A]⁰. Therefore, rate equation:

Q17. Identify A in the given diagram.  

• 1) Average rate of reaction
• 2) Order of reaction
• 3) Concentration of the catalyst
• 4) Instantaneous rate of reaction

Solution

Slope of the graph represents the instantaneous rate of reaction.

Q18. For a reaction the rate constants k₁ and k₂ calculated at two different temperatures T₁=500 K and T₂= 700 K are 0.025 s^-1 and 0.07s^-1 respectively. The values of A is:

• 1) 3.67
• 2) 10.1
• 3) 2.65
• 4) 1.61

Solution

 

Q19. The order of a reaction A + B  C is zero. Write its rate equation? 

Solution

Rate = k [A] ⁰ [B] ⁰

Q20. The reaction, 2N₂O (g) + O₂ (g)  2NO₂(g) proceeds through the following steps:      i)        NO + O₂  NO₃ (fast)     ii)        NO₃ +NO  NO₂ + NO₃ (slow) Predict the rate law expression for the reaction.

Solution

In the above reaction, the slowest step also called the rate determining step is NO₃ + NO  NO₂ + NO₃ Rate of the reaction = k [NO]² [O₂]

Q21. Differentiate between the order of a reaction and its molecularity.

Solution

Molecularity Order of a reaction i) It is the number of reacting species undergoing simultaneous collision in the reaction. i) It is the sum of the powers of the concentration terms in the rate law expression. ii) It is a theoretical concept. ii) It is determined experimentally. iii) It does not tell us anything about the mechanism of the reaction. iii) It tells us about the slowest step and hence gives some clues about the mechanism of the reaction. iv) It does not change with change in temperature and pressure. iv) It  changes with change in temperature And pressure.

Q22. Calculate the activation energy of a hydrogen carbon whose decomposition is given as follows: K= (4.5 x 10¹¹ s^-1) e^-28000K/T

Solution

According to Arrhenius equation k = A.e ^–Ea/RT Comparing the given value of k = (4.5 x 10¹¹ s^-1) e^{-28000 K/T}, we get,

Q23. The half-life of a first order decomposition of nitramide is 2.1 hour at 25^o C. Determine the time taken for the compound to decompose 99% of its original amount, rate constant = 0.2303 per hour.

Solution

Here a = 100 a – x = 100 – 99 = 1 t =

Q24. Which of the following statements is incorrect for the order of reaction:

• 1) Order of a reaction cannot be fractional.
• 2) Order of reaction can be determined experimentally.
• 3) Order of reaction is equal to the sum of the power of concentration terms in differential rate law.
• 4) Order of reaction is not affected with the stoichiometric coefficients of the reactants.

Solution

The order of the reaction can be zero, whole number or fraction. i.e,  0, 1, 2, 3 and a fraction.

Q25. The activation energies of two reactions are given as E_a1= 40 J and E_a2= 80 J, then the relation between their rate constants can be written as:

• 1) k₁ + k₂ = 0
• 2) k₁ > k₂
• 3) k₁ < k₂
• 4) k₁ = k₂

Solution

Use the relation    As the value of activation energy, E_a increases, the value of rate constant, k decreases.   So, k₁ > k₂ since E₁ < E₂    

Q26. State the main postulates of the collision theory.

Solution

According to the collision theory: i)                    A reaction occurs on collision of two molecules only if they possess a certain minimum amount of energy in excess of the normal energy of the molecules. ii)                   The minimum energy which molecules must possess before collision should be equal to or greater than the activation energy.

Q27. The rate of reaction between A and B increases by a factor of 100. Calculate the order of the reaction when the concentration of A is increased 10 times.

Solution

Q28. The activation energy for a reaction is zero. Calculate the value of its rate constant at 300 K, if k = 1.6 x 10⁶ s^-1 at 280 K? (R = 8.31 JK^-1 Mol^-1)

Solution

Q29. Define transition state or activation complex.

Solution

The arrangement of atoms corresponding to energy maxima (threshold energy) is called transition state or activated complex.

Q30. For a chemical reaction X Y, The rate increases by the factor 2.25 when concentration of X is increased by 1.5. Derive or suggest the rate law equation and find the order of reaction.

Solution

(Rate)₁ = k[X]m² (Rate)₂ = k [1.5X]^m Therefore, order of the reaction is 2. And rate law equation = k [X]²

Q31. The rate constant for the first order decomposition of certain reaction is described by the equation log k (sec^-1) = Calculate the activation energy for this reaction.

Solution

Given that log k =               …(i) According to Arrhenius equation k = Ae^-Ea/RT   Comparing equation (i) and (ii), we have

Q32. Define Collision frequency Z.

Solution

The number of collisions per second per unit volume of the reaction mixture is known as the collision frequency.