The relation between diffusive forces and fluxes is sometimes chosen on the basis of the entropy inequality. Since the form of the entropy inequality is influenced by the form of the thermal energy equation, a precise understanding of the latter is necessary when the matter of forces and fluxes is explored. Often the form of the thermal energy equation for multicomponent systems is developed on an intuitive basis, and this leads to uncertainty in the form of the entropy inequality. A detailed analysis of the thermal energy equation leads to the following term in the entropy inequality (A = N) Sigma (A = 1)(-del mu(A) + rho(-1)(A)del p(A)- rho(-1)(A)del.tau(A)). j(A) >= 0 in which del mu(A) and rho(-1)(A)del p(A) are the same order of magnitude. This result indicates that the use of the gradient of the chemical potential as a driving force for the diffusive flux is not justified. (C) 2011 Elsevier Ltd. All rights reserved.