Molar Flux and the Equation of Continuity

Your objectives in studying this section are to be able to  

State the equation of continuity for a system of variable composition. 

The equation of continuity for component A in a mixture describes the change of concentration of A with respect to time at a fixed point in space resulting from mass transfer of A and chemical reactions producing A. In vector symbolism, the resulting equation is (Bird et al., 1960)  

The first term in equation (1-63), the divergence of the molar flux vector, represents the net rate of molar efflux per unit volume. In rectangular coordinates, this term can be expanded as 

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