def isothermal_compressibility(V, dV_dP):
return -dV_dP/V<EOL>
r'''Calculate the isothermal coefficient of a compressibility, given its 
    molar volume at a certain `T` and `P`, and its derivative of molar volume
    with respect to `P`.

    .. math::
        \kappa = -\frac{1}{V}\left(\frac{\partial V}{\partial P} \right)_T

    Parameters
    ----------
    V : float
        Molar volume at `T` and `P`, [m^3/mol]
    dV_dP : float
        Derivative of molar volume with respect to `P`, [m^3/mol/Pa]

    Returns
    -------
    kappa : float
        Isothermal coefficient of a compressibility, [1/Pa]

    Notes
    -----
    For an ideal gas, this expression simplified to:

    .. math::
        \kappa = \frac{1}{P}

    Examples
    --------
    Calculated for hexane from the PR EOS at 299 K and 1 MPa (liquid):

    >>> isothermal_compressibility(0.000130229900873546, -2.72902118209903e-13)
    2.095541165119158e-09

    References
    ----------
    .. [1] Poling, Bruce E. The Properties of Gases and Liquids. 5th edition.
       New York: McGraw-Hill Professional, 2000.