Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R:
Assertion A: A reaction can have zero activation energy.
Reasons R: The minimum extra amount of energy absorbed by reactant molecules so that their energy becomes equal to threshold value, is called activation energy.
In the light of the above statements, choose the correct answer from the options given below:
Assertion A: A reaction can have zero activation energy.
Reasons R: The minimum extra amount of energy absorbed by reactant molecules so that their energy becomes equal to threshold value, is called activation energy.
In the light of the above statements, choose the correct answer from the options given below:
- Both A and R are true and R is NOT the correct explanation of A
- A is true but R is false
- A is false but R is true
- Both A and R are true and R is the correct explanation of A
The Correct Option is C
Approach Solution - 1
The assertion and reason need to be analyzed separately to evaluate their truth values and their relationship.
Assertion A: A reaction can have zero activation energy. In chemistry, activation energy refers to the minimum energy required for a chemical reaction to occur. While hypothetically, some reactions at molecular levels can proceed with negligible activation energy due to factors like enthalpy changes, a reaction truly having zero activation energy contradicts the fundamental energetic requirements for reaction initiation. Therefore, Assertion A is false.
Reason R: The minimum extra amount of energy absorbed by reactant molecules so that their energy becomes equal to the threshold value is called activation energy. This is a correct statement, as it accurately describes the concept of activation energy, which is the energy difference between the energy of the reactants and the energy of the activated complex.
Upon evaluation:
Assertion A: False
Reason R: True
The correct answer is: A is false but R is true.
Approach Solution -2
\(E_a\) is the smallest additional amount of energy that reactant molecules must absorb to reach the threshold value for their energy.
Therefore, The correct option is (C): A is false but R is true
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Concepts Used:
Chemical Kinetics
Chemical kinetics is the description of the rate of a chemical reaction. This is the rate at which the reactants are transformed into products. This may take place by abiotic or by biological systems, such as microbial metabolism.
Rate of a Chemical Reaction:
The speed of a reaction or the rate of a reaction can be defined as the change in concentration of a reactant or product in unit time. To be more specific, it can be expressed in terms of: (i) the rate of decrease in the concentration of any one of the reactants, or (ii) the rate of increase in concentration of any one of the products. Consider a hypothetical reaction, assuming that the volume of the system remains constant. R → P
Read More: Chemical Kinetics MCQ
Factors Affecting The Reaction Rate:
- The concentration of Reactants - According to collision theory, which is discussed later, reactant molecules collide with each other to form products.
- Nature of the Reactants - The reaction rate also depends on the types of substances that are reacting.
- Physical State of Reactants - The physical state of a reactant whether it is solid, liquid, or gas can greatly affect the rate of change.
- Surface Area of Reactants - When two or more reactants are in the same phase of fluid, their particles collide more often than when either or both are in the solid phase or when they are in a heterogeneous mixture. In a heterogeneous medium, the collision between the particles occurs at an interface between phases. Compared to the homogeneous case, the number of collisions between reactants per unit time is significantly reduced, and so is the reaction rate.
- Temperature - If the temperature is increased, the number of collisions between reactant molecules per second. Increases, thereby increasing the rate of the reaction.
- Effect Of Solvent - The nature of the solvent also depends on the reaction rate of the solute particles.
- Catalyst - Catalysts alter the rate of the reaction by changing the reaction mechanism.