Question

A 5.00 L flask contains 0.02 moles oxygen at 22°C, what is its pressure, in kilopascals? What is the pressure in atm?

Answer 1

The pressure of the gas is 10 kPa or 0.1 atm.

This looks like the time to apply the Ideal Gas Law:

`color(blue)(|bar(ul(PV = nRT)|)`,

where

• `P` is the pressure
• `V` is the volume
• `n` is the number of moles
• `R` is the gas constant
• `T` is the temperature

We can rearrange the Ideal Gas Law to get

`P = (nRT)/V`

`n = "0.02 mol"`
`R = "8.314 kPa·L·K"^"-1""mol"^"-1"`
`T = "(22 + 273.15) K" = "295.15 K"`
`V = "5.00 L"`

`P = (nRT)/V = (0.02 color(red)(cancel(color(black)("mol"))) × "8.314 kPa·" color(red)(cancel(color(black)("L·K"^"-1""mol"^"-1"))) × 295.15 color(red)(cancel(color(black)("K"))))/(5.00 color(red)(cancel(color(black)("L")))) = "10 kPa"`

To calculate the pressure in atmospheres, repeat the calculation using the value

`R = "0.082 06 L"·"atm"·"K"^"-1""mol"^"-1"`

`P = (nRT)/V = (0.02 color(red)(cancel(color(black)("mol"))) × "0.082 06 L·" color(red)(cancel(color(black)("atm"·"K"^"-1""mol"^"-1"))) × 295.15 color(red)(cancel(color(black)("K"))))/(5.00 color(red)(cancel(color(black)("L")))) = "0.1 atm"`