Collision Theory of Chemical Reactions - UNSOLVED PRACTICE SET

Q7. State the two main conditions necessary for a collision to be effective according to collision theory.

Q8. Why does increasing the temperature increase the rate of reaction according to collision theory? Explain in terms of kinetic energy and collision frequency.

Q9. Explain why the reaction between NO₂ and CO to form NO and CO₂ requires proper orientation of the colliding molecules, even when they have sufficient energy.

Q10. The reaction between two complex organic molecules often has a low steric factor (P << 1). What does this indicate about the reaction?

Q11. Why does increasing the concentration of reactants increase the rate of reaction according to collision theory?

Q12. Distinguish between "collision frequency" and "effective collision frequency." Which one directly determines the rate of reaction?

Q13. Explain the collision theory of chemical reactions in detail. Discuss the conditions for effective collisions and explain how temperature and concentration affect the rate of reaction based on this theory.

Q14. (a) What is meant by the "steric factor" or "probability factor" (P) in collision theory? Why is it necessary?

(b) For a reaction A + B → Products, the collision frequency is Z and the fraction of molecules with energy ≥ Ea is f. Write the expression for the rate of reaction according to collision theory.

(c) Why does collision theory often predict a higher rate than is experimentally observed?

Q15. (a) Explain why not all collisions lead to a chemical reaction, even at high temperatures.

(b) The activation energy of a reaction is 80 kJ/mol. At 300 K, calculate the fraction of molecules having energy equal to or greater than the activation energy. (Use the formula f = e^(-Ea/RT))

(c) What happens to this fraction when the temperature is increased to 320 K? Calculate and compare.

Q16. For a gaseous reaction A + B → Products, the following data is given at 300 K:

Collision frequency (Z) = 10³⁰ collisions per second per litre

Activation energy (Ea) = 50 kJ/mol

Steric factor (P) = 0.1

R = 8.314 J K⁻¹ mol⁻¹

(a) Calculate the fraction of molecules (f) having energy ≥ Ea at 300 K.

(b) Calculate the rate of reaction using the collision theory expression: Rate = P × Z × f

(c) If the temperature is increased to 320 K (assuming Z remains approximately the same), calculate the new fraction f and the new rate.

(d) By what factor does the rate increase?

Q17. The reaction between hydrogen and iodine: H₂ + I₂ → 2HI has an activation energy of 165 kJ/mol.

(a) Calculate the fraction of molecules having sufficient energy to react at 500 K.

(b) Calculate the same fraction at 600 K.

(c) By what factor does the rate increase when temperature is raised from 500 K to 600 K? (Assume collision frequency and steric factor remain constant.)

(d) Explain why this reaction, despite having a high activation energy, can still proceed at a measurable rate at 500 K.

Q18. In your school chemistry lab, your teacher demonstrates the reaction between sodium thiosulphate and dilute HCl:

Na₂S₂O₃ + 2HCl → 2NaCl + SO₂ + S + H₂O

A white precipitate of sulphur makes a cross placed under the flask disappear.

(a) According to collision theory, explain what must happen for this reaction to occur at the molecular level.

(b) When the concentration of Na₂S₂O₃ is doubled (keeping HCl constant), the cross disappears faster. Explain this using collision theory.

(c) When the temperature is increased by 10°C, the cross disappears approximately twice as fast. Explain this observation using the concepts of collision frequency and activation energy.

(d) Why is it important that the S₂O₃²⁻ ions and H⁺ ions collide with the proper orientation for the reaction to proceed?