Question

A chemical reaction occurs as a result of collision between reacting molecules. Therefore, the reaction rate is given by:

A. total number of collisions occurring in a unit volume per second
B. fraction with molecules which possess energy less than the threshold energy
C. total number of effective collisions
D. none of the above

Answer 1

Hint:We know that, rate or speed of a chemical reaction is the change in concentration of product or reactant in unit time. Specifically rate is expressed in the form of decrease in reactant concentration or increase in concentration of products.

Complete step by step answer:
Let’s first understand the collision theory given by William Lewis and Max Trautz in 1916-18. This theory says that the reactant molecules are in the shape of a sphere (hard) and reaction occurs only when they collide with each other. The number of collisions occurring in one second in one unit volume of reaction mixture is termed as collision frequency.
But not all collisions result in chemical reactions. The collisions in which collisions of molecules occur possessing sufficient kinetic energy and proper orientation of reactants, so as to facilitate bond breaking between reactants and forming new bonds to form products is termed as effective collision. So, we can say that only effective collisions lead to product formation. Therefore, the rate of the reaction is given by effective collision.

Hence, the correct answer is option C.

Additional Information:

The dependence of rate constant on temperature is given by the equation of Arrhenius.

$k = A{e^{ - Ea/RT}}$


Here, ${E_a}$ is activation energy, A is Arrhenius factor, R is gas constant, T is temperature and k is rate constant.

The equation shows that, increase of temperature lowers ${E_a}$ which results in an increase of rate of reaction.


Note:
Always remember that, rate of the reaction is dependent on many factors such as temperature, effect of catalyst, surface area of the reactant etc. For rise of temperature by $10^\circ {\rm{C}}$, the rate constant is doubled nearly. A catalyst fastens the reaction without getting consumed in the reaction.