The equilibrium pressure of [tex]H_{2}[/tex] is 288 torr. and [tex]K_{p}[/tex] for this reaction is 0.786 atm.
from the reaction:-     [tex]2AsH_{3}[/tex] ⇄ [tex]2As + 3H_{2}[/tex]
initial concentration   392 torr.        0
at equilibrium. Â Â Â Â Â Â Â 392 - [tex]2x[/tex]. Â Â Â Â Â Â Â [tex]3x[/tex]
and the final pressure in the flask = 488 torr.
Hence,
[tex]( 392 - 2x ) + 3x = 488\\ x = 488-392\\x = 96 torr.[/tex]
The partial  pressure of [tex]H_{2}[/tex] is 3 × 96 =  288 torr.
and [tex]AsH_{3}[/tex] is 392 - ( 2 × 96 ) = 392 - 192 = 200 torr.
Now, to find [tex]K_{p}[/tex] for this reaction, we will use [tex]K_{p} = \frac{(P_{H_{2} })^{2} }{( P_{AsH_{3} } )^{2}}[/tex]
putting all the values, we get,
[tex]K_{p} = \frac{(288)^{3} }{(200)^{2} }[/tex]
   = 597.1968 torr.
   = 0.786 atm.  ( 1 atm = 760 torr. )
what do you mean by equilibrium?
Equilibrium in chemistry is the phase that exists when a chemical reaction and its opposite reaction happen at the same rates. This word's Latin origin dates back to the prefix aequi-, which means equal, and lbra, that indicates scale or balance.
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