<prompt> The electrical potential difference necessary for a single ion to be at equilibrium across a membrane is best described by theGoldman equationvant Hoff equationFicks lawNernst equation  <response>: At normal body temperature 37degC, the electrical difference that will balance a given concentration difference of univalent ions--such as Na ions--can be determined from the following formula, called the Nernst equation.Ref: Guyton; 13th edition; Chapter 4 Transpo of Substances Through Cell Membranes 