AIIMS 2006 Chemistry Transition State Theory Assertion Reason Question

To understand the question regarding the Transition State Theory (TST) in chemical kinetics, let’s analyze both the assertion and the reason step by step.

Assertion:

According to transition state theory, for the formation of an activated complex, one of the vibrational degrees of freedom is converted into a translational degree of freedom.

Explanation: Transition state theory posits that during a chemical reaction, reactants must overcome a certain energy barrier to form products. This energy barrier is reached at the transition state, or activated complex. The transition state is characterized by a high-energy arrangement of atoms, and it is the point at which the reactants have sufficient energy to convert into products.

In this context, vibrational degrees of freedom refer to the modes in which atoms within a molecule can vibrate. When forming the activated complex, some of this vibrational energy can be transformed into translational energy (which is associated with the overall movement of the molecule). This exchange is crucial as it helps the system reach the transition state where the reactants can effectively convert into products.

Reason:

Energy of the activated complex is higher than the energy of reactant molecules.

Explanation: In TST, the activated complex indeed has a higher energy than that of the reactants. This is because energy must be supplied to overcome the activation energy barrier, which is the difference in energy between the energy of the reactants and the energy of the activated complex. Mathematically, this can be represented as:

$E_{\text{activated complex}} = E_{\text{reactants}} + E_{\text{activation}}$

where $E_{\text{activation}}$ is the energy required to form the activated complex. This higher energy state signifies that the activated complex is unstable and will quickly convert to products or revert to reactants.

Conclusion:

Both the assertion and reason are true statements, and the reason correctly explains the assertion. The conversion of vibrational energy to translational energy is part of the process that allows the system to reach the higher energy state of the activated complex.

Correct Answer:

A) If both assertion and reason are true and reason is the correct explanation of the assertion.

Justification of Incorrect Options:

• B) If both assertion and reason are true but reason is not the correct explanation of the assertion.

  • This option is incorrect because the reason provided does indeed explain why the assertion is true.

• C) If assertion is true, but reason is false.

  • This option is incorrect because both the assertion and reason are true.

• D) Both assertion and reason are false statements.

  • This option is incorrect because both the assertion and reason are true.

Summary:

In summary, the transition state theory provides a framework for understanding how reactants can form products by overcoming an energy barrier, and both the assertion and reason accurately reflect key concepts in this theory. Thus, the correct answer is A.