Question

Which of the following are not the permitted values of molecularity? a. 0 b. 2 c. 5 d. 1

Short answer

Options 'a' (0) and 'c' (5) are not permitted values of molecularity.

Step-by-step solution

Identify Molecularity Descriptions

Molecularity refers to the number of molecules or atoms that come together to react in an elementary reaction. It is always a positive integer, indicating the number of reacting species involved in the collision leading to a reaction.

Inspection of Option 'a',''

The option 'a' is 0. Since molecularity cannot be zero, as it would mean no molecules are participating in a reaction, this is not a permitted molecularity.

Inspection of Option 'b'

In the case of option 'b', the value is 2, which is an integer value and is allowed as molecularity can be unimolecular (1), bimolecular (2), or termolecular (3). Thus, 2 is a permitted value.

Inspection of Option 'c'

Option 'c' is 5. Although it is a positive integer, molecularities greater than three are uncommon because higher-order reactions are rare and often impractical due to the low probability of more than three molecules colliding simultaneously. Therefore, 5 is typically not considered a valid molecularity.

Inspection of Option 'd'

Option 'd' is 1, which corresponds to unimolecular reactions, a common type of reaction. Therefore, 1 is a permitted value for molecularity.

Key concepts

Understanding Elementary Reactions

An elementary reaction consists of simple steps where molecules or atoms respond to collisions. The term "elementary" implies that the reaction happens in a single step without intermediate phases. Understanding these reactions is key because they represent the fundamental building blocks of more complex reactions.
Elementary reactions can be classified by the number of participating molecules, known as the reaction's molecularity. For example:

• Unimolecular: Involves a single reacting species transitioning independently.
• Bimolecular: Involves two reacting molecules colliding and reacting.
• Termolecular: Consists of three molecules, though this is less common due to the low probability of such a collision occurring.

Elementary reactions help us simplify and better understand complex chemical processes.

Delving Into Reaction Orders

Reaction order offers an insight into how the concentration of one or more reactants affects the rate of the reaction. It's not determined solely by the molecularity but rather by observing the kinetics of the reaction.
Kinetics studies reveal:

• First-order reactions, where the rate depends on the concentration of a single reactant.
• Second-order reactions can depend on either two molecules of one species or one of each of two species.
• Zero-order reactions, where the rate is independent of the reactant concentrations.

The reaction order is crucial for calculating the rate laws and predicting how changes in concentration will impact overall reaction speed. Unlike molecularity, which is always a whole number, reaction orders can also be fractional or even zero.

Exploring Collision Theory

Collision theory provides an explanation for how and why reactions occur, focusing on the molecular level during collisions. It states that for a reaction to happen, atoms or molecules must collide with sufficient energy and appropriate orientation.
This energy, known as the activation energy, represents the minimum threshold needed to break and form chemical bonds during collisions.

• Not all collisions result in a chemical reaction; only those with the right energy and orientation succeed.
• Increasing temperature can boost the fraction of successful collisions by providing more energy to the molecules.
• Catalysts are often used to lower the activation energy barrier, increasing reaction rates without being consumed in the reaction.

Understanding collision theory aids in manipulating conditions to improve reaction efficiency, which is vital in both industrial processes and natural phenomena.