[NISHANT]

Q:60 ml of H2 nd 42ml of I2 are heated in a closed vessel.At eq. the vessel contains 28ml of HI.Calculate the degree of dissociation of HI.

here nowhere is it written that pressure is constant during the reaction,therefore is it right to consider volume of the substances proportional to their moles and use the volumes of the given substances in the same way as we would have used the moles??

please help.

[Demotivator]

yes, assuming ideal behavior.

[NISHANT]

YES OR NO?
I DID NOT UNDERSTAND.
IF YES THEN IF THE PRSSURE OF ANY SUBSTANCE IS CHANGING HOW CAN THE VOLUME BE PROPORTIONAL TO MOLES?

[Demotivator]

Those volumes are proprtional to moles according to the law of combining volumes for gases, provided the volumes are measured at fixed temp and pressure for all gases. I assume 60 ml, etc are a measure of a gas as virtually isolated outside the vessel (ie in a measuring vessel at fixed pressure). Otherwise, how can it be, since a gas's actual volume is the volume of the reaction vessel itself?

H2 + I2 -> 2HI
Equal moles of HI produced for reactants consumed.
Therefore, The total pressure in the reaction vessel is constant and individual pressures are proportional to moles (Dalton's law of partial pressures).
Of course, the pressure can vary if the temperature is different but it affects all components the same way.

[Donaldson Tan]

i agree with demotivator