An example of passive transport is ion fluxes through Na, K, Ca, and Cl channels. Unlike active transport, passive transport is powered by the arithmetic sum of osmosis (a concentration gradient) and an electric field (the transmembrane potential). Formally, the molar Gibbs free energy change associated with successful transport is Δ Δ G = R T ln ⁡ ⁡ ( c i n c o u t ) + ( F z ) V m e m b r a n e where R represents the gas constant, T represents absolute temperature, z is the charge per ion, and F represents the Faraday constant.