SK025 CHAPTER 1 REACTION KINETICS

1. Given the reaction below: NH₄⁺ (aq) + NO₂⁻ (aq) → N₂ (g) +2H₂O (l) The following data was obtained in a study on the kinetics of the reaction. The rate law for the reaction is ....

• rate = k [NH₄⁺ ] [NO₂⁻ ]
• rate = k [NH₄⁺ ]² [NO₂⁻]²
• rate = k [NH₄⁺ ]² [NO₂⁻]
• rate = k [NH₄⁺ ] [NO₂⁻]²

2. Which of the following changes with time for the first order reaction?

I Rate of reaction

II Half-life

III Rate constant

• I only
• I and II
• II and III
• I, II and III

3. The rate equation for the reaction, A → products, is given as rate = k [A]². The units of the rate constant, k, are...

• s⁻¹
• mol dm⁻³ s⁻¹
• dm⁶ mol⁻¹ s⁻¹
• dm³ mol⁻¹ s⁻¹

4. When the concentration of the reactant molecules is increased, the rate of reaction increases because ....

• the average kinetic energy of the reactant molecules increases.
• the frequency of the molecular collisions increases.
• the rate constant increases.
• the activation energy increases.

5. A first order reaction, A → products, has the rate constant of 2.0 x 10⁻⁴ s⁻¹ at 400 K. In one of the experiments, the concentration of A was 2.0 M. The half-life of the reaction is ....

• 48 minutes
• 68 minutes
• 58 minutes
• 83 minutes

6. At 25 ⁰C, a first order reaction is half completed in 625 s. What is the rate constant for the reaction?

• 6.65 x 10⁻² min⁻¹
• 6.65 x 10⁻² mol dm⁻³ min⁻¹
• 1.11 x 10⁻³ min⁻¹
• 1.85 x 10⁻⁵ min⁻¹

7. The distribution of kinetic energy for gaseous molecules at 298 K and 308 K are shown in the Maxwell-Boltzmann curve as in the picture attached. Which of the following statements explains most accurately the reason why the reaction rate of the molecules in the gas sample increases twofold when the temperature is raised from 298 K to 308 K?

• The area below the curve 298 K is twice the area below the curve at 308 K.
• The average speed of the molecules increases by two-fold.
• The number of collisions between molecules increases by two-fold.
• The number of molecules that possess energy equal to or more than Eₐ increase by two-fold.

8. The activation energy of a certain reaction is 250 kJ/mol. If the rate constant at T₁ = 300 K is k₁ and the rate constant at T₂ = 320 K is k₂, calculate the ratio of the reaction rates at 320 K and 300 K.

• 3.0 x 10⁻²⁹
• 6.7 x 10⁻²
• 15.0
• 525.8

9. Which of the following statements does not describe the role of a catalyst in a reaction?

• A catalyst lowers the magnitude of activation energy in a reaction.
• A catalyst provides an alternative mechanism which has a lower activation energy compared to the general reaction.
• A catalyst speeds up the rate of reaction without itself being changed chemically.
• A catalyst shortens the time taken for a reversible reaction to achieve equilibrium without changing the concentration constant, Kc.

10. A chemical reaction has the rate constant of 0.0158 dm⁶ mol⁻² s⁻¹ at 540 K. If the Arrhenius constant is 4.68 dm⁶ mol⁻² s⁻¹, what is the activation energy for the reaction?

• 2.5 kJ/mol
• 25.5 kJ/mol
• 5.0 kJ/mol
• 50.0 kJ/mol