\documentclass{standalone}
\usepackage{tikz}
\usepackage{pgfplots}
\usepackage{siunitx}
\pgfplotsset{compat=newest}
\usetikzlibrary{arrows.meta}
\begin{document}
	\begin{tikzpicture}
		\begin{axis}[
			xmin=0.5,
			xmax=3.5,
			ymin=0,
			ymax=25,
			axis x line=middle,
			axis y line=middle,
			axis line style = {-Latex},
			xticklabels={},
			xtick = {1.203,2.74},
			ytick = {5.685,12,18},
			yticklabels={$p_0$,$p_0+\Delta p_2$,$p_0+\Delta p_1$,$p_0+\Delta p_1$},
			ylabel = Druck $p$,
			%y unit = {Pa},
			xlabel = Volumen $V$,
			%x unit = {m^3},
			grid=none
		    ]
		
			\addplot[very thick, blue, domain={1.203:2.74}]{((18*1.203^(1.4)/(x^1.4)};
			\draw[very thick, blue](axis cs:2.74,5.6858)--(axis cs:1.203,5.6858)--(axis cs:1.203,12);
			\draw[very thick, blue, dotted](axis cs:1.203,12)--(axis cs:1.203,18);
			\node[anchor=south] at (axis cs: 1.203,18){\textbf{I},$\;T_0$};
			\node[anchor=west] at (axis cs: 2.74,5.686){\textbf{II},$\;T_1$};
			\node[anchor=north] at (axis cs: 1.203,5.686){\textbf{III},$\;T_1$};
			\node[anchor=east] at (axis cs: 1.203,12){\textbf{IV},$\;T_0$};
		
			\node[circle,minimum size=1mm,inner sep=0pt,fill=black,draw] at (axis cs: 1.203,18){};
			\node[circle,minimum size=1mm,inner sep=0pt,fill=black,draw] at (axis cs: 2.74,5.686){};
			\node[circle,minimum size=1mm,inner sep=0pt,fill=black,draw] at (axis cs: 1.203,5.686){};
			\node[circle,minimum size=1mm,inner sep=0pt,fill=black,draw] at (axis cs: 1.203,12){};

		\end{axis}
	\end{tikzpicture}
\end{document}