Practice free Chemical Kinetics (Chemistry) NEET multiple-choice questions online with instant answers and detailed explanations. No login required.
Threshold energy, as defined in the context of collision theory, is equal to:
The NCERT text defines it in a footnote: '* Threshold energy = Activation Energy + energy possessed by reacting species.'
Collision theory predicts rate constants fairly accurately for reactions involving:
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.'
If the steric factor (P) for a reaction is very small, it indicates that:
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.
Which two factors together determine the criteria for an effective collision and hence the rate of a chemical reaction, according to collision theory?
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.'
Collision theory is based on aspects of which fundamental theory?
The NCERT text mentions, 'It is based on kinetic theory of gases.'
An increase in temperature generally leads to an increase in the rate of reaction. How does collision theory explain this phenomenon?
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.
Given below are two statements: one is labelled Assertion A and the other Reason R.
Assertion A: A reaction can have zero activation energy.
Reason 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:
Zero $E_a$ is possible if reactants already possess threshold energy; R correctly defines $E_a$ and explains A.
For a certain reaction, the rate $= k[A]^2[B]$. When the initial concentration of A is tripled keeping concentration of B constant, the initial rate would:
Rate $\propto [A]^2$; tripling A $\Rightarrow$ rate $\times 3^2 = 9$.
Which one is an example of heterogeneous catalysis?
Haber process — gases over solid Fe catalyst — is heterogeneous.
Activation energy of any chemical reaction can be calculated if one knows the value of:
Arrhenius: $\ln(k_2/k_1) = (E_a/R)(1/T_1 - 1/T_2)$ — need $k$ at two $T$.
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