Reduced size

The term reduced size is used with a specific meaning in thermodynamics . There it describes the dimensionless quotients of an intensive variable such as pressure etc. and the value of the relevant variable at the critical point as a reference value (index for critical ). If two substances are in states with the same reduced sizes, they also have comparable properties in certain areas. ${\displaystyle _{\mathrm {c} }}$

Reduced pressure

${\displaystyle p_{\mathrm {r} }={\frac {p}{p_{\mathrm {c} }}}}$

Reduced temperature

${\displaystyle T_{\mathrm {r} }={\frac {T}{T_{\mathrm {c} }}}}$

Reduced molar volume

(or indirectly reduced density , because the mass is constant):

${\displaystyle V_{\mathrm {m,r} }={\frac {V_{\mathrm {m} }}{V_{\mathrm {m,c} }}}={\frac {\rho _{\mathrm {m,c} }}{\rho }}}$

application

With the reduced quantities, the Van der Waals equation can be formulated in a reduced form:

${\displaystyle \left(p_{\mathrm {r} }+{\frac {3}{V_{\mathrm {r} }^{2}}}\right)(3V_{\mathrm {r} }-1)=8T_{\mathrm {r} }}$