# Transport Phenomena Exam 2 Key Equations

Mass flux
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In Fick's Law, why is there a negative sign before the product of mass diffusivity and concentration gradient?
a. the negative sign makes the concentration gradient always positive
b. the sign of the mass flux is always the opposite of the sign of the concentration gradient
c. this makes the mass flux always go in the positive direction
d. all of the above
e. none of the above