def Tm_depression_eutectic(Tm, Hm, x=None, M=None, MW=None):
if x:<EOL><INDENT>dTm = R*Tm**<NUM_LIT:2>*x/Hm<EOL><DEDENT>elif M and MW:<EOL><INDENT>MW = MW/<NUM_LIT> <EOL>dTm = R*Tm**<NUM_LIT:2>*MW*M/Hm<EOL><DEDENT>else:<EOL><INDENT>raise Exception('<STR_LIT>')<EOL><DEDENT>return dTm<EOL>
r'''Returns the freezing point depression caused by a solute in a solvent.
    Can use either the mole fraction of the solute or its molality and the
    molecular weight of the solvent. Assumes ideal system behavior.

    .. math::
        \Delta T_m = \frac{R T_m^2 x}{\Delta H_m}

        \Delta T_m = \frac{R T_m^2 (MW) M}{1000 \Delta H_m}

    Parameters
    ----------
    Tm : float
        Melting temperature of the solute [K]
    Hm : float
        Heat of melting at the melting temperature of the solute [J/mol]
    x : float, optional
        Mole fraction of the solute [-]
    M : float, optional
        Molality [mol/kg]
    MW: float, optional
        Molecular weight of the solvent [g/mol]

    Returns
    -------
    dTm : float
        Freezing point depression [K]

    Notes
    -----
    MW is the molecular weight of the solvent. M is the molality of the solute.

    Examples
    --------
    From [1]_, matching example.

    >>> Tm_depression_eutectic(353.35, 19110, .02)
    1.0864594900639515

    References
    ----------
    .. [1] Gmehling, Jurgen. Chemical Thermodynamics: For Process Simulation.
       Weinheim, Germany: Wiley-VCH, 2012.