First Law of Thermodynamics Content
First Law of Thermodynamics
Let the initial volume of the system is V_{1} and initial internal energy is U_{1}. Let DQ_{P}_{ }the gas is heated from 

T1 K to T2 K. Addition of heat causes the following changes in the system:  
Internal energy increases from U_{1} to U_{2}.
Volume of the system increases from V_{1} to V_{2}. Temperature increases from T_{1} K to T_{2} K. Work (DW) is done by the gas on the piston. 

According to the first law of

thermodynamics: 
DQ = DU+ DW
But DW = PDV Thus DQ_{P}_{} = DU+ PDV As DV = (V_{2} – V_{1}) DQ_{P}_{} = DU+ P (V_{2} – V_{1}) 

GRAPHICAL REPRESENTATION


Graph between P & V for an isobaric process is a straight line which is parallel to Vaxis.  