The speed of the gas particles in the sealed flask in question here will decrease as it enters the freezer because the motion of the gas particles will slow down.
Based on the kinetic molecular theory of gases, the temperature of the gas is a measure of the average kinetic energy of the molecules.
Since the freezer makes substances cool and temperature drops, the kinetic energy of the gases will substantially drop. Kinetic energy is the energy due to the motion of a body.
Air has a heat capacity of about 700 Joules per kg per °K and a density of just 1.2 kg/m3, so its initial energy would be 700 x 1 x 1.2 x 293 = 246,120 Joules
