TABLE OF CONTENTS The treatment of viscosity variations included the possibility of variable density. Equations (8.12) and (8.52) assumed constant density, constant 
, and constant ? T. We state here the appropriate generalizations of these equations to account for variable physical properties.
| (8.74) |  |
| (8.75) |  |
For completeness, axial diffusion and variable cross-section terms were included in Equations (8.74) and (8.75). They are usually dropped. Also, the variations in 
and ? are usually small enough that they can be brought outside the derivatives. The primary utility of these equations, compared with Equations (8.12) and (8.52), is for gas-phase reactions with a significant pressure drop.
