Question

The proportionality constant, k, used in rate laws is exponentially dependent on temperature. Which of the following best explains the reason for this temperature dependence?
A . As T increases, reacting molecules decrease their average kinetic energy resulting in fewer collisions, and the rate constant decreases.
B. As T increases, reacting molecules increase their average kinetic energy resulting in more collisions, and the rate constant increases.
C . As T increases, reacting molecules increase resulting in more effective collisions between reacting molecules, and the rate constant increases.
D . As T increases, the orientation requirements (shown by the variable A) for the reaction become less critical, A increases, and the rate constant increases

Answer 1

Hint: The rate of reaction is the speed at which a chemical reaction proceeds. It is often expressed in terms of either the concentration (amount per unit volume) of a product that is formed in a unit of time or concentration of a reactant that is consumed in a unit of time. The rate constant is the rat of the reaction at 1 molar concentration of the reactant or product.

Complete step by step answer:
According to the Arrhenius theory the equation is, \[k = A{e^{ - \,\dfrac{{{E_a}}}{{RT}}}}\]
Where, \[{E_a}\] is the activation energy, T is the temperature, R is the gas constant. A is the frequency factor or Arrhenius constant.
Now, \[{e^{ - \,\dfrac{{{E_a}}}{{RT}}}}\] is the ratio of the number of molecules with average kinetic energy to the total number of molecules.
With increasing the temperature the value of \[{e^{ - \,\dfrac{{{E_a}}}{{RT}}}}\] increases i.e. as T increases, reacting molecules increase their average kinetic energy resulting in more collisions, and the rate constant increases.
So, the correct answer is, B

Additional information: The rate of reaction refers to the speed at which the products are formed from the reactants in a chemical reaction. It gives some insight into the time frame under which a reaction can be completed. Reaction kinetics is the study of the rate of chemical reactions, and reaction rates can vary greatly over a large range of time scales. The two main factors that affect the rate of a chemical reaction are the nature of reactants and surface area.
According to the collision theory, increasing the concentration of one or more reactants increases the rate of reaction because a higher concentration of a reactant leads to more collisions of that reactant in a specific time scale. The physical state of reactants, number of reactants, and complexity of reaction affects in such a way that the rate of reaction is generally slower in liquids when compared to gases and slower in solids when compared to liquids. So, the size of the reactant also affects. The smaller the size of the reactant faster is the reaction.
Few more important factors are:
1) An increase in temperature increases the rate of reaction due to a rise in the average kinetic energy of the reactant molecules. Thus, a greater proportion of molecules will have the minimum energy that is necessary for an effective collision.
2) A catalyst is a substance that accelerates a reaction by participating in it without being consumed and increases the rate of the reaction without actually participating in the reaction. It increases the speed of reaction in both forward and reverses reaction by following an alternate pathway that has lower activation energy.

Note:If reactant molecules exist in different phases in a heterogeneous mixture, the rate of reaction is limited by the contact surface area of the phases. The surface area of reactants affects the rate of reaction such that if the size of a particle is small, the surface area will be more and this increases the speed of heterogeneous chemical reactions.