$6\mathrm{.}10.$ The critical step in Motorola's proposed process for producing ultra pure

solar$-$cell grade silicon is the reaction

$Si([$ commercial grade, $],[$ solid, $98\%$ pure $])+Si{F}_4([$ gas, $],[$ pure $])2Si{F}_2([$ gas, $],[$ pure $])dots$ exothermic

The $Si{F}_2$ is then decomposed elsewhere to produce pure silicon. Thermody$-$

namics says that at the chosen operating temperature of $1,350K,$ the reaction

should only become appreciable when the pressure falls below $100Pa.$ The

reactor will be a vertical $0\mathrm{.}4-m-i.$d$.$ tube packed with $6-mm$ silicon particles

$(=0\mathrm{.}5).$ Reactant gas $($pure $Si{F}_4)$ will enter the reactor at $2,000Pa$ and $1,350K,$

and $1\mathrm{.}2m$ downstream we expect the pressure to have dropped to $100Pa.$ From

here on reaction takes off and conversion to product is soon complete. Estimate

the production rate of silicon $(k\frac{g}{h})$ obtainable from this reactor.

Data:

${}_{Si{F}_4}=4{10}^{-5}k\frac{g}{m}s(estimated)$

$(mw{)}_{Si}=0\mathrm{.}028$

$(mw{)}_{Si{F}_4}=0\mathrm{.}104$

$(\frac{C_p}{C_v}{)}_{Si{F}_4}=1\mathrm{.}15(estimated)$