def bC_Mg_SO3_RZM91(T, P):
    """c-a: magnesium sulfite [RZM91]."""
    b0 = -2.8
    b1 = 12.9
    b2 = -201
    C0 = 0
    C1 = 0
    alph1 = 1.4
    alph2 = 12
    omega = -9
    valid = T == 298.15
    return b0, b1, b2, C0, C1, alph1, alph2, omega, valid
