Lecture 1 – Exothermic Reactions

ACKNOWLEDGEMENT:

Figure	Source of Figure
Figure 1	http://chemistry.tutorvista.com

Chemical reactions:

All chemical reactions can be broadly classified into 2 categories:

i.                    Endothermic Reactions

ii.                  Exothermic Reactions

Enthalpy; ∆H:

Enthalpy, denoted by H is defined as the heat content or the internal energy of the compounds.

Change in enthalpy or ∆H:

Change in enthalpy or ∆H is given by:

∆H = H_Products – H_Reactants

Activation energy:

Activation energy is defined as the minimum energy required by all reactions for initiation.

For example; a match stick must be rubbed to produce heat of friction and then it starts burning.

Exothermic Reactions:

Exothermic reactions are defined as those reactions in which energy/heat is released as a product of the reaction.

Figure 1:

Figure 1 shows the energy diagram of an exothermic reaction. It can be seen that:

1. the internal energy of the reactants is higher than the internal energy of the products. 
2. Therefore, the enthalpy or ∆H of such reactions is always negative. 
3. Products formed by such reactions are more stable as compared to their parent reactants. 
4. The bonds formed are stronger and it requires large amounts of energy to break them. Thus, in terms of bond formation; Bond making is Exothermic.

Examples of Exothermic Reactions:

i.                   Combustion:

Combustion is a reaction of any substance with Oxygen evolving heat and light.

ii.                 Respiration:

Respiration is breakdown of food to release energy in living organisms.

iii.            Neutralization:

Neutralization is the reaction between an acid and a base to form salt and water. The reaction evolves heat.

iv.               Displacement reaction in metals:

Displacement reaction in metals is when a more reactive metal displaces a lesser reactive metal from its salt solution.

Some displacement reactions are exothermic.