Question

Rate of a chemical reaction is not influenced by the:

• A. Catalyst
• B. Temperature
• C. Reactants concentration
• D. Number of molecules of reactants taking part in a reaction

Hint:

Think of baking a cake. The recipe (stoichiometry - number of eggs, flour, etc.) tells you what you need and in what proportions, but the oven temperature and whether you use a catalyst (like baking powder) determine how fast it bakes.

Answer 1

The Correct Option is D

Step 1: Understand the factors that influence the rate of a chemical reaction. 
The rate of a chemical reaction is determined by several factors that affect the frequency and energy of collisions between reactant molecules. These factors include: Temperature: Generally, increasing the temperature increases the rate of a reaction because it increases the kinetic energy of the molecules, leading to more frequent and more energetic collisions (more molecules possess the activation energy required for the reaction). Concentration of reactants: Increasing the concentration of reactants typically increases the reaction rate because there are more reactant molecules in a given volume, leading to a higher frequency of collisions. Catalyst: A catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. It does this by providing an alternative reaction pathway with a lower activation energy. Surface area of solid reactants or catalysts: For reactions involving solids, increasing the surface area increases the contact between reactants, thus increasing the reaction rate. Pressure (for gaseous reactions): Increasing the pressure of gaseous reactants increases their concentration, leading to a higher reaction rate.
Step 2: Analyze the role of the number of molecules taking part in a reaction (stoichiometry). 
The number of molecules of reactants as indicated by the balanced chemical equation (stoichiometry) does not directly influence the rate of the reaction. The stoichiometry determines the molar ratios in which reactants combine and products are formed, but the speed at which this occurs is governed by the factors mentioned in Step 1. The molecularity of an elementary reaction (the number of molecules that collide simultaneously) can affect the rate law, but the overall stoichiometry of a complex reaction (which may involve multiple elementary steps) does not, by itself, determine the rate. The rate law must be determined experimentally. 
Step 3: Evaluate each option. 
Option 1 (Catalyst): Catalysts significantly influence the rate of a reaction.
Option 2 (Temperature): Temperature has a strong effect on the reaction rate (Arrhenius equation).
Option 3 (Reactants concentration): The concentration of reactants directly affects the frequency of collisions and thus the reaction rate (as described by the rate law).
Option 4 (Number of molecules of reactants taking part in a reaction): This refers to the stoichiometry of the reaction, which does not directly influence the rate. The rate depends on how often effective collisions occur, which is related to concentration, temperature, and the activation energy (affected by a catalyst), not just the number of molecules that will eventually react according to the balanced equation. 
Step 4: Select the factor that does not influence the rate of a chemical reaction. 
The number of molecules of reactants taking part in a reaction (stoichiometry) does not directly influence the rate of the reaction.