Question

What is a rate determining step?

Answer 1

The rate-determining step is the slowest step in a reaction mechanism. It limits the overall rate of the reaction because the rate of the entire reaction is governed by the rate of this step. In a multi-step reaction, the rate-determining step is the step with the highest activation energy or the slowest rate.

Answer 2

A complex reaction involves more than one elementary reaction step. These reactions occur through a sequence of individual reactions, each involving the collision and interaction of reactants. A complex reaction can have multiple intermediates and may involve different molecular species at various stages.

Answer 3

The rate constant of a reaction generally increases with temperature. This is explained by the Arrhenius equation, which shows that the rate constant \(k\) increases exponentially with an increase in temperature. As the temperature rises, the number of molecules having sufficient energy to overcome the activation energy barrier increases, leading to an increase in the rate constant.
\[ k = A \cdot e^{-\frac{E_a}{RT}} \]
Where:
- \(k\) is the rate constant,
- \(A\) is the frequency factor,
- \(E_a\) is the activation energy,
- \(R\) is the gas constant,
- \(T\) is the temperature in Kelvin.

Answer 4

Molecularity refers to the number of reacting species involved in an elementary reaction and is a property of that specific step. It applies only to elementary reactions because these reactions occur in a single step and involve a fixed number of reacting molecules. On the other hand, the order of a reaction is determined experimentally and refers to the relationship between the concentration of reactants and the rate of the overall reaction, which can apply to both elementary and complex reactions.

Answer 5

For a second-order reaction, the rate of the reaction is proportional to the square of the concentration of reactant \(X\): \[ \text{Rate} = k \cdot [X]^2 \]
If the concentration of \(X\) is increased 3 times, the rate of formation of \(Y\) will increase by a factor of: \[ \left( 3 \right)^2 = 9 \]
Thus, the rate of formation of \(Y\) will increase by a factor of 9 when the concentration of \(X\) is increased 3 times.