Chemistry MCQs for NEET — Practice Questions with Answers

The NCERT text mentions, 'Collision theory also has certain drawbacks as it considers atoms/molecules to be hard spheres and ignores their structural aspect.'

The NCERT text provides an example: 'For example, formation of methanol from bromoethane depends upon the orientation of reactant molecules... The proper orientation of reactant molecules lead to bond formation whereas improper orientation makes them simply bounce back and no products are formed.' This directly illustrates the significance of proper orientation.

The NCERT text states, 'Comparing (3.23) with Arrhenius equation, we can say that A is related to collision frequency.' Also, 'A (Arrhenius factor or pre-exponential factor) corresponds to the collision frequency.'

The NCERT text defines it in a footnote: '* Threshold energy = Activation Energy + energy possessed by reacting species.'

Chapter states, 'Equation (3.23) predicts the value of rate constants fairly accurately for the reactions that involve atomic species or simple molecules but for complex molecules significant deviations are observed.'

The steric factor (P) accounts for proper orientation. A small P value means that only a small fraction of collisions have the correct orientation, implying that a specific orientation is very important and difficult to achieve for the reaction to proceed.

The NCERT text explicitly states, 'Thus, in collision theory activation energy and proper orientation of the molecules together determine the criteria for an effective collision and hence the rate of a chemical reaction.'

The NCERT text mentions, 'It is based on kinetic theory of gases.'

While not explicitly stated in one sentence as an explanation of temperature effect by collision theory, the underlying principles are present. Increased temperature leads to higher kinetic energy of molecules, thus increasing the collision frequency (Z) and, more significantly, increasing the fraction ($e^{-E_a/RT}$) of molecules possessing energy equal to or greater than the activation energy, making more collisions effective. The Arrhenius equation ($k = Ae^{-E_a/RT}$) shows a direct dependence of k on temperature. And based on collision theory, A relates to collision frequency, and $e^{-E_a/RT}$ relates to the fraction of molecules with sufficient energy, both of which are positively influenced by temperature.

According to the NCERT text, 'However, it may be remembered that rotation around a C-C single bond is not completely free. It is hindered by a small energy barrier of 1-20 kJ mol$^{-1}$ due to weak repulsive interaction between the adjacent bonds.' Therefore, the statement that rotation is completely free is incorrect.