So basically, Z is the charge on the ion. It could be positive negative one, positive negative two, positive negative three. Now, if we're dealing with an uncharged neutral molecule, z is zero. And so the delta G is zero, because that neutral charge will not feel any type of electric force within that voltage difference. So essentially, this is the equation that we can basically use to tell us how much energy we have to input. We have to give a charged molecule or ion to basically move it across that particular voltage difference.