Concept of enthalpy and some problems based on enthalpy

Enthalpy: Definition, Characteristics, and Example Problem

Enthalpy refers to the total heat content of a system, calculated by adding its internal energy to the product of its pressure and volume.

  H=U+PV

   Where H=Enthalpy of the system
              U = The internal energy contained within the system
              P = The pressure exerted by the system
              V = The volume occupied by the system

Characteristics of Enthalpy: 

1) It is an extensive property of the system
2) It is a state function. This means, similar to internal energy, it is determined solely by the system's initial and final states, not by the process or path taken between them.

Q. A gas undergoes expansion at constant temperature, increasing its volume from 10 L to 100 L under a pressure of 1 atm. Calculate the work done, the change in internal energy, and the heat exchanged.

Ans: If it is not stated in the problem the gas is allowed to reversibly expand, we always considered the expansion is irreversible. So the process is irreversible. 
    
      \(\tt w=-P_{2}(V_{2}-V_{1})\)
          
             \(\tt P_{2}\)=final pressure =1 atm
             \(\tt V_{1}\)=initial volume =10 L
             \(\tt V_{2}\)=final volume =100 L
   
            \(\tt =-1(100-10)\)
            \(\tt =-90\) L.atm

According to first law of thermodynamic

  \(\tt \triangle U=q+w\)

        Where U = the system’s internal energy
             q = the amount of heat transferred or absorbed
        \(\tt \triangle U\)=0 [\because temperaure is constant
 
  \(0=-90+q\) [\(\because\) \(\tt w=-90\) L.atm]
 \(\therefore\) \(q=90\) L.atm