Question

For a given reaction, the concentration of the reactant plotted against time gave a straight line with negative slope. The order of the reaction is (a) 3 (b) 2 (c) 1 (d) 0

Short answer

The order of the reaction is (d) 0, as indicated by the constant rate demonstrated by the straight line with a negative slope on the concentration vs time graph.

Step-by-step solution

Understand the significance of the concentration vs time graph for a reaction

When analyzing chemical kinetics, the rate at which reactants are consumed can be studied by measuring their concentration over time. The graph of concentration vs. time can indicate the order of a reaction: a zero-order reaction has a constant rate and will display as a straight line with a constant negative slope; a first-order reaction will show a curve that indicates exponential decay; and second or higher-order reactions will also show curves, often steeper than first-order reactions.

Determine the reaction order from the linear graph

Because the problem states that the concentration of the reactant vs. time graph is a straight line with a negative slope, the reaction proceeds at a constant rate regardless of the concentration of the reactant. This behavior is characteristic of a zero-order reaction.

Select the correct answer

Based on the behavior of the concentration vs time graph, we have determined that the reaction is zero-order. The correct answer is option (d) 0.

Key concepts

Chemical Kinetics

In chemistry, understanding how reactions occur and at what speed is crucial. Chemical kinetics is the study of the rates at which chemical reactions proceed and the factors affecting those rates.

It involves analyzing how reaction conditions like temperature, pressure, and concentration influence the speed of the reaction. In the context of an educational exercise, students may be asked to interpret graphs which represent the concentration of a reactant over time. Such exercises help them master the concepts of reaction rates and the methods used to measure and calculate them.

Chemical kinetics is not only about the speed of reactions but also encompasses the pathway and the mechanism by which a reaction occurs. Understanding kinetics can help predict the yield of products and optimize conditions for industrial chemical processes.

Rate of Reaction

The rate of a chemical reaction refers to how fast the reactants are converted into products. This concept is fundamental in the study of chemical kinetics and essential for students to grasp. The rate can be expressed as the change in the concentration of reactants or products per unit time.

A key point for students to understand is that the rate of a reaction is not constant. It varies with changes in the concentration of the reactants, the temperature, and the presence of catalysts. Exercises involving the graphical representation of reaction rates, as seen in the given problem, are specifically designed to illustrate how these rates can be deduced from experimental data.

Being proficient in interpreting such data prepares students for more advanced studies, as well as practical laboratory work where they will measure reaction rates and use this knowledge to infer reaction mechanisms.

Zero-Order Reaction

In zero-order reactions, the rate is constant and does not change with the concentration of reactants. This type of reaction is less common than first or second-order reactions but is crucial in certain scenarios like enzyme-catalyzed processes in biochemistry.

For students encountering this concept in exercises, it's important to recognize the straight-line graph with a constant negative slope as indicative of a zero-order reaction. Unlike first-order reactions that often involve radioactive decay, where the rate is directly proportional to the concentration of the reacting substance, zero-order reactions maintain the same rate regardless of how much reactant is left.

Understanding the characteristics of zero-order kinetics is vital for students, especially since it deviates from the often more intuitive understanding of reactions speeding up with increased concentration of reactants. With this foundation, students will be better equipped to handle complex problems involving reaction rates and kinetics.