def isentropic_exponent(Cp, Cv):
    """
    Calculate the isentropic coefficient of a gas, given its constant-
    pressure and constant-volume heat capacity.

    .. math::
        k = \\frac{C_p}{C_v}

    Parameters
    ----------
    Cp : float
        Gas heat capacity at constant pressure, [J/mol/K]
    Cv : float
        Gas heat capacity at constant volume, [J/mol/K]

    Returns
    -------
    k : float
        Isentropic exponent, [-]

    Examples
    --------
    >>> isentropic_exponent(33.6, 25.27)
    1.329639889196676

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