# Isobaric change of state

Isobaric change of state in the pV diagram

The isobaric change of state is a term used in thermodynamics . It describes a change in state during which the pressure in the system remains constant. According to Gay-Lussac's law or the equation of state of an ideal gas :

${\ displaystyle {V_ {1} \ over T_ {1}} = {V_ {2} \ over T_ {2}} \ \ mathrm {const.}}$

It also follows from this that the volumes behave like the corresponding absolute temperatures :

${\ displaystyle {V_ {2} \ over V_ {1}} = {T_ {2} \ over T_ {1}}}$

According to the first law of thermodynamics ( ), the following relationships result for the work : ${\ displaystyle \ Q = \ Delta U- \ W}$ ${\ displaystyle \ W}$

${\ displaystyle \ W = -p \ cdot \ Delta V = -nR \ cdot \ Delta T}$

Here p denotes the pressure , n the amount of substance (in mol ) and R the general gas constant .

In order to heat a gas to a certain temperature under isobaric conditions, a larger amount of heat has to be supplied than with isochoric heating, since part of the supplied heat has to be applied for the expansion of the gas.