8.98 dm3 of hydrogen gas is collected at 38.8 °C. Find
the volume the gas will occupy
at -39.9 °C if the pressure
remains constant.

6.71dm³

Explanation:

Given parameters:

Initial Volume of hydrogen gas  = 8.98dm³

Initial Temperature  = 38.8°C; in Kelvin  = 38.8 + 273  = 311.8K

Final temperature = -39.9°C; in Kelvin  = -39.9 + 273  = 233.1K

Unknown:

Final volume = ?

Solution:

To solve this problem, we apply the Charles's law. It states at;

   "The volume of a fixed mass (mole) of a gas varies directly as its absolute temperature if the pressure is constant".

  Mathematically;

            =      

V and T are temperature values

1 and 2 are the initial and final states

 Insert the parameters and solve for V₂

        =

         V₂ x 311.8 = 8.98 x 233.1

          V₂  = 6.71dm³