Chapter 9.4, Problem 1QQ

Interpretation Introduction

Interpretation:

From the given options, one which describes the three core concepts of collision theory has to be identified.

Concept Introduction:

Collision theory:

Collision theory explains why different reactions occurs at different rates.  It is used to explain or predict the rate of a reaction.  For a chemical reaction to occur the molecules or the reacting species must collide with each other.  Chemical reaction is dependent on the number of collisions between the reactants.  The three important parts of collision theory are, the reactant must collide, the reactant must collide with sufficient energy and the collision must be of proper orientation.

Molecular Collisions:

For a chemical reaction to happen, the molecule must collide with each other.  Most of the reactions are carried out in liquid or gaseous state.  In liquid and gaseous state, molecules are free to move which makes the collision easier.  Solid reactant can also undergo collisions but the problem is only molecules present on the surface can participate in collision.  More they collide, more will be the reaction rate.

Activation Energy:

For a reaction to occur, the reactant molecules must collide with some minimum amount of energy.  This minimum amount of energy for a reaction to occur is known as activation energy.  Every reaction will have different activation energy.  Activation energy is dependent on temperature.  As the temperature increases, molecules will move faster and the activation energy decreases.

Collision Orientation:

Reactants must be oriented in a way such that the collisions become effective and leads to product formation.  Collision orientation is a factor which determines the reaction for non-spherical molecules or atoms.

Example:

${\text{H}}_{\text{2}}{\text{C=CH}}_{\text{2}}\text{+HCl}\stackrel{}{\to }{\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{Cl}$

In this reaction, the double bond is converted to single bond.  Hydrogen atom is attached to one of the carbon and chlorine to the other carbon.  The reaction will happen only if hydrogen approaches the carbon-carbon double bond.  High concentration of negative charge will be there on the double bond.  Chlorine atom is also partially negative, so here the way they hit each other ie, the orientation will determine the reaction.