Question

8) Base your answer on the information below. A rigid cylinder is fitted with a movable piston. The cylinder contains a sample of helium gas, He(g), which has an initial volume of 125.0 milliliters and an initial pressure of 1.0 atmosphere, as shown below. The temperature of the helium gas sample is 20.0°C. Handle 0 2.0 Movable piston L3.04 Pressure gauge -1500 mL 125.0 ML -100.0 mL -75.0 mL -50.0 mL -25.0 mL ATM Rigid cylinder Helium gas is removed from the cylinder and a sample of nitrogen gas, N2(g), is added to the cylinder. The nitrogen gas has a volume of 125.0 milliliters and a pressure of 1.0 atmosphere at 20.0°C. Compare the number of particles in this nitrogen gas sample to the number of particles in the original helium gas sample.

Answer 1

Both the Helium and Nitrogen gases are kept in identical Pressure, temperature and volume are also constant. So according to Avogadro's Law, we know that gases of the same volumes, kept in identical temperatures and pressures contain equal number of molecules.

Hence, the number of particles in the nitrogen sample and the original helium gas sample would be the same!

One can also verify the above Avogadro's Law if we assume both nitrogen and helium behaves ideally. Consider the ideal gas equation, $PV=nRT$, where n=no. of moles of gas.

If you fix the other variables such as P, V, and T, the remaining R is the gas constant, so automatically n i.e the no. of moles of gas for both will be equal for both.