There is a large specific surface area in a dispersed cell, so much so that there are some notable differences in thermodynamic quantities for a chemical reaction in the cell because of the strong surface effect. The thermodynamic relations between the electromotive force (emf) and the dispersity of a cell and between each of thermodynamic properties and the dispersivity of the cell are derived, and the effects of degree of dispersion of substances in the cell on the emf and the thermodynamic properties are discussed. The results show that the emf, the equilibrium constant, the: entropy for reaction, the heat of reaction, and the enthalpy of reaction vary with the dispersivities of the reactants or/and the products in the cell. And two new concepts, surface emf and dispersion cell, are put forward in this paper.