Question

A substance which decreases the rate of a reaction is a/an (a) inhibitor (b) poison (c) moderator (d) promoter

Short answer

The correct answer is (a) inhibitor.

Step-by-step solution

- Analyzing the Choices A and B

(a) An inhibitor, in chemistry, typically works by reducing the rate of a specific reaction. The molecule of an inhibitor would bind with a reactant, thus preventing it from reacting further. (b) A poison, while it can indeed slow down some types of reactions, especially enzyimatic ones, is not the main term used in chemistry to describe a substance that slows down a reaction.

- Analyzing Choices C and D

(c) A moderator is a substance used in nuclear reactors to slow down the speed of neutrons. Although it does slow down a specific type of reaction, the term is mainly used within the context of nuclear physics, not chemical reaction rate control. (d) A promoter, contrarily, improves the catalytic properties of a catalyst and thus speeds up the reaction, it does not slow it down.

- Choosing the Correct Answer

After analyzing each choice, it becomes clear that the term which most directly refers to a substance that decreases the rate of a typical chemical reaction is an inhibitor. Thus, (a) inhibitor is the correct answer.

Key concepts

Inhibitor

An inhibitor plays a significant role in the dynamics of chemical reactions. Its primary function is to slow down or decrease the rate at which a reaction proceeds. This can be achieved through various mechanisms, but one common method is by an inhibitor molecule binding to a reactant. This prevents the reactant from participating in the reaction, effectively reducing the reaction's overall speed.

For example, imagine two chemicals that normally react quickly when mixed. If we introduce an inhibitor into the mixture, it would act like a roadblock, preventing the two chemicals from coming together as readily, and thus lowering the reaction rate. This concept is essential not only in laboratory settings but also in various industries where managing reaction rates is critical, such as in the production of pharmaceuticals where inhibitors are used to regulate the activity of enzymes.

Catalysis

Catalysis is the counterpart to inhibition in chemical reactions. While an inhibitor slows down a reaction, a catalyst does the opposite – it accelerates a reaction without itself being consumed or undergoing permanent change. This marvel of chemistry is fundamental in both biological processes and industrial applications.

As an educator, when explaining catalysis, it's helpful to use real-world examples, such as enzymes in our bodies that aid in digestion. These biological catalysts speed up reactions to ensure that we can metabolize food efficiently. In industry, catalysts can be found in the manufacture of various chemicals, where they allow reactions to occur faster or under more mild conditions, which can be energy saving and cost-effective. Understanding the principles of catalysis is vital for students to grasp how chemical processes can be controlled and optimized.

Reaction Kinetics

Reaction kinetics, as a topic, dives into the rates at which chemical reactions occur and the factors that affect these rates. The study of reaction kinetics involves understanding how different variables—such as concentration of reactants, temperature, and presence of a catalyst or inhibitor—affect the speed of a reaction.

Let's consider cooking as an analogy to explain this concept. Similar to how the heat setting on a stove will affect how quickly a meal cooks, in chemistry, the temperature can influence how rapidly a reaction proceeds. Higher temperatures usually increase reaction rates, just as turning up the heat on the stove cooks food faster. Moreover, just as stirring can help combine ingredients more effectively, increasing the concentration of reactants can lead to more frequent collisions and a faster reaction. Knowing the fundamentals of reaction kinetics is vital for students as it provides the basis for predicting how changes in conditions can alter the speed of a reaction, which is crucial in both academic and practical chemistry tasks.