Chemical Kinetics - SS2 Chemistry Past Questions and Answers - page 5

For a second-order reaction, the rate equation is given by:

rate = k[A]²

We can rearrange the equation to solve for the concentration:

rate = k[A]²

[A]² = rate / k

[A] = sqrt(rate / k)

Given that the rate constant (k) is 0.005 M^-1s^-1 and the initial concentration ([A]₀) is 0.20 M, we can substitute these values into the equation:

[A] = sqrt(rate / k) = sqrt([A]₀² - 2kt)

[A] = sqrt((0.20 M)² - 2 x 0.005 M^-1s^-1 x 60 s)

[A] ≈ 0.173 M

Therefore, the concentration of the reactant after 60 seconds is approximately 0.173 M.

Collision theory is a fundamental concept in understanding the rate of chemical reactions. It proposes that for a reaction to occur, reactant particles must collide with sufficient energy and proper orientation. The collision theory provides the following principles:

a.    Collision Frequency: For a reaction to take place, reactant particles must collide. The collision frequency is determined by the concentrations of the reactants and their molecular speeds. Higher concentrations and increased kinetic energy (temperature) lead to more frequent collisions.

b.    Activation Energy: Reactant particles must possess a minimum amount of energy, known as the activation energy, to initiate a reaction. The activation energy is required to break the existing chemical bonds and allow new bonds to form. Only collisions with sufficient energy equal to or greater than the activation energy result in a reaction.

c.     Effective Collisions: Not all collisions lead to a reaction. For a collision to be effective, the colliding particles must have the proper orientation. This ensures that the necessary bond-breaking and bond-forming processes occur during the collision.

Based on collision theory, increasing the concentration of reactants or raising the temperature increases the collision frequency, leading to a higher rate of reaction. Additionally, a higher temperature provides more energy to reactant particles, increasing their kinetic energy and the likelihood of collisions with sufficient energy to overcome the activation energy barrier.