Final answer:
The pressure of light molecules is the same as that of heavy molecules, but their speeds differ, with light molecules moving faster. In balloons filled with different gases but identical in other conditions, the pressure is the same but molecular speeds vary, with helium molecules moving faster than propane. The balloon's pressure matches the room pressure if it starts at 1 atmosphere.
Step-by-step explanation:
The pressure exerted by 100 light molecules is the same as the pressure exerted by 100 heavy molecules in the same volume container at the same temperature, due to the principles underlying the ideal gas law. However, the speed of the light molecules is greater than the speed of heavy molecules because the kinetic energy, which depends on both mass and velocity, must be the same for both gases at the same temperature; hence lighter molecules move faster.
In the case of balloons filled with different gases but identical in size, temperature, and material, the pressure in the helium balloon is the same as the pressure in the propane balloon. However, the speed of the molecules in the helium balloon is greater than the speed of the molecules in the propane balloon, again due to the difference in molecular masses. Finally, if the balloon's pressure is at 1 atmosphere initially, and considering the membrane of the balloon provides a negligible inward pressure, the pressure inside the helium balloon is the same as the pressure in the room.