### SimuLab 11: Dalton's Law

In our simulation it is more convenient to use number of particles instead of number of moles. Moreover, in the simulation units the Boltzmann constant k=1. Hence, the partial pressures

 Pi= Ni V T,

where Ni is just a number of molecules of certain type.

 Your objective is to: Recognize why the total pressure of the gas mixture is equal to the sum of partial pressures of the components from the microscopic point of view. You will be able to: State Dalton's Law. State the relationship between the number of particles and pressure they exert at constant temperature and volume. Calculate the final pressure as the number of particles are varied when the initial pressure and number of particles are given.

Copy the table below.

 N/V P T 100 Blue and 100 Green 100 Blue 100 Green

 1. Open SMDPlayer, select IntroDalton'sLaw from the IdealGas folder. PRESS Play. Read all the captions and follow the instructions. Go to File -Quit
 Movies gives a preliminary understanding of partial pressures from a microscopic point of view.

 2. Open SMD, select Dalton in the IdealGas folder.
 You are visualizing 100 green particles with a mass of 1.00 and 100 blue particles each with a mass of 10.0 as shown in Figure 2.7.

Figure 2.7: Screenshot of Dalton's Law SimuLab.

 3. Change the Iterations Between Displays to 500. Select Show Averages.
 Increasing Iterations speeds up the simulation.

 4. Press Start and run the simulation for approximately 40 time units. Press Pause. Record in your table the number density  N/V, pressure P and temperature T from the averaging window.
 The system is approaching equilibrium.

 5. Select Edit : Edit Particles and choose Remove all G particles. Press Reset Averages in the Average Values panel. Repeat Step 4. Note that the blue particles have a mass of 10.
 You are are collecting data for future analysis.

 6. Select File : Reset Experiment. Select Edit : Edit Particles and choose Remove all B particles. Repeat Step 4. Note that the green particles have a mass of 1.
 7. Using the data recorded in your table, add the pressure of the 100 blue particles to that of the 100 green particles
 You are summing partial gas pressures.

 Q2.64: Compare this calculated result to the total pressure of the mixture when both blue and green particles were present. Explain what you find.

 Q2.65: Does the mass of a particle affect the pressure it exerts? Justify your answer.

 Q2.66: What is the relationship between the number of particles present and the pressure they exert in a given container?

 8. Select File : Reset Experiment. Select Edit : Edit Particles and choose Remove particles to remove any 20 particles on the screen.
 You are lowering the density.

 Q2.67: What do you predict the pressure will now be?

 9. Select Reset Averages in the Average Values panel. Press Start and wait for 40 time units. Press Pause.
 The system is approaching equilibrium.