SSS 2: ENERGY AND CHEMICAL REACTION

Energy can be defined as the capacity to do work. 

                     Forms of Energy

The different forms of Energy are:

1. Mechanical energy 

2. Chemical energy 

3. Electrical energy 

4. Heat energy 

5. Nuclear energy 

6. Light (Photon) energy 

7. Sound energy 

8. Magnetic energy 

All matter possess energy in one form or the other. When energy changes from one form to another, the total amount of energy before and after the change are always the same. This is the law of conservation of energy.

       The law of conservation of energy states that energy can neither be created nor destroyed but it can be changed from one form to another.

     Energy changes in chemical reactions

Energy changes occur during chemical reactions because the reactants and products possess different amounts of chemical energy. The forms of energy changes that may accompany a chemical reaction include:

I. Heat: For example, when a strong acid reacts with a strong base.

II. Light and Heat: For example, when magnesium burns in air or in an oxy-ethyne flame.

III. Sound and Heat: For example, when a mixture of hydrogen and oxygen is ignited.

                       Heat content

Heat content is also called enthalpy (H). It is the energy possessed by a chemical substance.

                       Heat of reaction

Heat of reaction is also called enthalpy change (ΔH). It is the amount of heat energy absorbed or released during a chemical reaction at constant pressure.

      It represents the difference in energy between the products and the reactants:

The unit used for measuring heat change is the joule(J). The common unit is kilojoule(KJ).

The two types of energy changes that accompany a chemical reaction are:

I. Exothermic reaction 

II. Endothermic reaction 

                 Exothermic reaction

Exothermic reaction is the type of reaction in which heat is liberated to the surrounding.