where 1 and 2 refer to the entropy production rate generated by the inflows or outflows of chemical substances Ri and that generated by the chemical reactions in an ORN, respectively. In equation (3a), 𝜇 𝑖 ex and 𝜇 𝑖 in are the chemical potentials for Ri in the exterior and interior of an ORN, respectively, and V and T are the volume and temperature of the ORN, respectively. Thus, 𝑘 d𝑖 𝑉(𝐶 𝑖 ex -𝐶 𝑖 in ) refers to the rate of the inflow or outflow of Ri and (𝜇 𝑖 ex -𝜇 𝑖 in ) 𝑇 ⁄ refers to the thermodynamic force for the inflow or outflow of Ri. In equation (3b),  𝑗 expresses the rate of the 𝑗-th reaction, defined by