Chapter 6, Problem 18A

Summary Introduction

Introduction:

A catalyst is a chemical that increases the rate of a chemical reaction without affecting itself by the reaction. Catalysts typically speed up a reaction by decreasing the activation energy or changing the reaction mechanism. Enzymes are proteins that act as catalysts in biochemical reactions.

Answer to Problem 18A

Correct answer :

The correct answer is option C. a catalyst.

Explanation of Solution

Explanation/justification for the correct answer :

Option C. a catalyst. Catalyst is a substance that modifies the transition state to lower the activation energy; they are composed only of protein or small molecule cofactor is termed an enzyme. A catalyst increases the rate of reaction without being consumed in the reaction. So, the correct answer is option C.

Explanation for incorrect answer :

Option A. an ion. Ions are electrically charged atom or group of atoms formed by the loss or gain of one or more electrons. So, this is an incorrect answer.

Option B. a reactant. Reactant is a substance that takes part in and undergoes change during a reaction. So, this is an incorrect answer.

Option D. a substrate. Substrate is the starting material for an enzymatic chemical reaction. There may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. So, this is an incorrect answer.