Question

The statement which is true in respect of order of a reaction is (a) it is always a whole number (b) it is always a fraction (c) it may be zero, a whole number or a fraction (d) it can never be a fraction

Short answer

The correct answer is (c): the order of a reaction may be zero, a whole number, or a fraction.

Step-by-step solution

Understand the Order of a Reaction

The order of a reaction is defined as the power to which its concentration term in the rate equation is raised. It is experimentally determined, and can be zero, a whole number, or a fraction.

Eliminate Incorrect Answers

Looking at options (a) and (b), those statements are not correct as the reaction order is not 'always' a whole number or a fraction. It could be, but it also could be zero. Therefore, these options can be eliminated as they are not inclusive of all possibility.

Choose the Correct Answer

In option (d), the statement is incorrect as the order of a reaction can indeed be a fraction in some cases. Therefore, option (c) is the correct answer because it correctly includes all possibilities: the order of a reaction may be zero, a whole number, or a fraction.

Key concepts

Chemical Kinetics

Chemical kinetics is the study of how quickly or slowly chemical reactions occur. It provides insights into the speed, or rate, of reactions and the steps involved in the transformation of reactants into products.
Understanding chemical kinetics is crucial for numerous applications such as developing chemical processes, pharmaceuticals, and even environmental science efforts. Kinetics tells you not just the rate at which reactions proceed, but also how changing conditions can accelerate or slow down these rates.
You may hear terms like 'reaction mechanism' and 'transition state' often when studying kinetics. These refer to the pathway and energy profile that guide a reaction. Knowing these can help predict and manipulate how and when a reaction will occur.

Reaction Rate

The reaction rate is an essential part of chemical kinetics. It defines how fast a reactant is converted into a product over time. More technically, it's the change in concentration of reactants or products per unit time.
For example, if you observe the concentration of a reactant decreasing quickly, the reaction rate is high. Conversely, if the concentration changes slowly, the reaction rate is low.

• A high reaction rate means that products are formed quickly, which might be useful in industrial processes.
• A low rate could be desirable for controlled reactions, like rusting of metal over years.

Understanding reaction rates help in tailoring reaction conditions to achieve the desired outcome, remaining a pivotal aspect of both research and industry.

Rate Equation

A rate equation mathematically expresses the relationship between the reaction rate and the concentrations of reactants. It is typically written as:
\[ \text{Rate} = k[A]^m[B]^n \]
where \(k\) is the rate constant, and \([A]\) and \([B]\) are the concentrations of reactants A and B.

• The exponents \(m\) and \(n\) are orders of the reaction with respect to each reactant. These are experimentally determined and reveal how changes in concentration affect the rate.
• Overall order of reaction is the sum of these exponents.

Rate equations are fundamental for predicting reaction behaviors and making calculations on how changes in conditions like concentration will affect the rate, making them an essential aspect of chemical engineering and laboratory work.