Question

What fraction of the gas phase molecules initially present for 1.0 atm in the chamber are present at 1.0×10−10 torr?

Answer 1

The fraction of gas phase molecules is calculated by the division of final pressure to the initial pressure.

Fraction = $\frac{P_{final}}{P_{initial}}$     (1)

Here, initial pressure = 1.0 atm

final pressure = $1.0\times 10^{-10} torr$

First, convert torr into atm

1 atm = 760 torr

final pressure = $\frac{1.0\times 10^{-10}}{760}$

= $1.316\times 10^{-13}atm$

Now, put the value of initial and final pressure in formula (1)

Fraction = $\frac{1.316\times 10^{-13}atm}{1.0 atm}$  

= $1.316\times 10^{-13}$  

Thus, fraction of the  gas phase molecules = $1.316\times 10^{-13}$ $\simeq 1.3\times 10^{-13}$