Question

Ten grams of a gas occupies 12.5 liters at a pressure of 42.0 cm Hg. What is the volume when the pressure has increased to 75.0 cm Hg?

Answer 1

At constant temperature, and constant amount of gas, `P_1V_1=P_2V_2`.

Explanation:

So all we have to do is convert the `cm*Hg` into a pressure reading, and calculate `V_2`.

`1*atm-=760*mm*Hg`; of course, given the relationship the units of pressure cancel out.

`V_2=(P_1V_1)/P_2` `=` `(12.5*Lxx420*mm*Hg)/(750*mm*Hg)` `~=` `7*L`.

Note that here we use a unit of length to measure the pressure. That is `1*atm` will support a column of mercury that is `760*mm` high. Ordinarily, you would be expected to calculate the pressure with authentic units of `kPa` or `"atmospheres"`. Here, we can afford to be a little slack.