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0.75 mole of solid $A_4$ and 2 mole of gaseous $O_2$ are heated to react completely in sealed vessel to produce only one gaseous compound B.After the compound is formed the vessel is brought to initial temperature,the pressure is found to half the initial pressure.What is molecular formula of compound?

$\begin{array}{1 1}(a)\;A_3O_4&(b)\;A_2O_6\\(c)\;AO_2&(d)\;A_2O_4\end{array}$

1 Answer

$A_4+O_2\rightarrow B$
Since initial pressure is due to $O_2$(2 mole) and find pressure is due to B only( a mole)
Now $P\propto mole$ of $O_2\propto 2$(T remains constant)
$\large\frac{p}{2}$$\propto mole\; of\; B\propto a$
In other words only 1 mole of B is formed
The mole ratio of $A_4 : O_2$ is $B=0.75 : 2$ as ratio of atoms of A and O in B
$\Rightarrow 4\times 0.75 : 2\times 2$
$\Rightarrow 3 : 4$
Thus B is $A_3O_4$
Hence (a) is the correct answer.
answered Jan 7, 2014 by sreemathi.v

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