If vapour pressures of pure liquids 'A' and 'B' are 300 and 800, torr respectively a

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1.Solution and Colligative properties

medium

If vapour pressures of pure liquids $'A'$ and $'B'$ are $300$ and $800\, torr$ respectively at $25\,^oC$. When these two liquids are mixed at this temperature to form a solution in which mole percentage of $'B'$ is $92$, then the total vapour pressure is observed to $0.95\, atm$. Which of the following is true for this solution?

$\Delta {V_{mix}} > 0$

$\Delta {H_{mix}} < 0$

$\Delta {V_{mix}} = 0$

$\Delta {H_{mix}} = 0$

Solution

According to Raoult's law $P_{T}=(0.08 \times 300+0.92 \times 800)$ torr
$=(24+736)$ torr
$=760$ torr $=1$ atm $P_{ exp }=0.95 atm <1 atm$
Hence the solution shows $-$ve deviation . so $\Delta H_{\operatorname{mix}}<0,$ and $\Delta V_{\operatorname{mix}}<0$

Standard 12

Chemistry