= Isentropic compressibility
{title2=$\kappa_S=-V^{-1}(\partial V/\partial P)_{S,N}$}
= Adiabatic compressibility
{synonym}
Isentropic compressibility is the <compressibility> at fixed <entropy>, particle number and composition. The conventional name adiabatic compressibility refers to a reversible <adiabatic process>; an irreversible <adiabatic compression> need not keep <entropy> fixed. For an <ideal gas>, it is $\kappa_S=1/(\gamma P)$, where $\gamma=C_P/C_V$ is the <heat capacity ratio>. It describes a steeper local pressure response than <isothermal compressibility> when $\gamma>1$.
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