Wie rechne ich... eine isotherme Zustandsänderung?

clear all;
%Konstanten
k_B = 1.38064852e10-23
k_B = 1.3806e+10
R = 8.3144598
R = 8.3145
pStd = 1013.25e2
pStd = 101325
TZeroK = 273.15
TZeroK = 273.1500
g = 9.81
g = 9.8100
%Gegeben
T1 = 20 + TZeroK
T1 = 293.1500
p1 = 2.5*1e5
p1 = 250000
p2 = 5*1e5
p2 = 500000
kappa = 1.4
kappa = 1.4000

T2 = (p1^(1-kappa) * T1^kappa / p2^(1-kappa))^(1/kappa)
T2 = 357.3539