Question

Exothermic Vs. Endothermic Reaction

Reaction progress diagrams for single-step endothermic and exothermic reactions.

a. Devise a general statement about the relationship between Ea and the rate of a reaction. 


b. Describe the effect of temperature on the energy of collisions, and explain how this effect changes the rate of a reaction. 


c. State three things that resulted in an increase in the rate of the reaction. For each of the three things, explain at a molecular level what happens to cause the rate of the reaction to increase. 


Answer 1

a. If a reaction has a high activation energy, the number of molecules possessing that amout of energy will be less. As a result the effective collisions will be less. A collision is said to be effective if it occurs between two mollecules possessing the minimum energy barrier, that is, Ea.

b. Increasing the temperature increases the average kinetic energy of the molecules, which in turn raises the number of molecules possessing energy greater than activation energy. Thus the number of effective collisions increase and this results in an increase in reaction rate.

c. Reaction rate can increase because of the following 3 factors :

1. Increasing the temperature, because it increases the average kinetic energy of molecules as mentioned in part (b) above

2. Presence of catalyst increases the reaction rate because the catalyst lowers the activation energy required for an effective collision due to which the number of effective collisios increase hence increasing the reaction rate.

3. Increasing conc. of reactant can also increase the reaction rate because it increases the number of molecules possessing energy greater than Ea, thus the number of effective collisions are increased.