Classification Of Energy in First Law Of Thermodynamics

It can be defined as the ability to do work or the ability to produce an effect.   

   

                                                                                                                                                                                                       
(i). Mechanical Energy: M E

    It is the energy in stored form, relative to other bodies. 
Potential energy is the gravitational energy possessed by a body, with respect to elevation above a reference plane.

P.E = mgz    Nm

Kinetic energy is due to the motion of the body with respect to the earth surface.

K.E = ½ mV2   Nm

M.E = mgz + ½ mV2        (M.E stored within the system consisting of a body some reference body)

(ii). Internal Energy:

    It represents the energy associated with relative molecular translation, molecular rotation, vibration, binding energy etc..,

    U- total internal energy     u = internal energy/unit mass

(iii). Potential Energy:

    Potential Energy is the energy of storage required to maintain the molecules in their position with respect to one another against the forces of mutual attraction and repletion.

Latent heat:

    One form of potential energy (internal energy) 
.Whenever a liquid is heated above its boiling point, 
phase change takes place with out raise in temperature.
 Here the heat added is stored as the internal potential 
energy, by increasing the distance between the molecules. 
This heat added during vapourisation is known as latent heat.


(iv). Kinetic Energy:

     Kinetic Energy is the energy contained within the molecular system due to their random motion. It varies with absolute temperature and is termed as sensible heat. Internal energy is actually stored within the single body.

Sensible heat:
    It is the energy required to raise the temperature.