Predict reaction and calculate E, cell = A voltaic cell is constructed from a standard Zn+ | Zn half cell (E red -0.763V) and a standard Mn2+ | Mn half cell (E red = -1.180V). What is the spontaneous reaction that takes place, and what is the standard cell potential? Spontaneous cell reaction: Write a balanced equation using the smallest integer coefficients possible. + from standard reduction potentials. Standard cell potential: V. +