UG-Gas-Properties-Activity

Gas Properties Simulation Activity In this activity you’ll use the Gas Properties PhET Simulation to explore and explain the relationships between energy, pressure, volume, temperature, particle mass, number, and speed. This activity has 5 modules: ○ Explore the Simulation ○ Kinetic Energy and Speed ○ Kinetic Molecular Theory of Gases ○ Relationships between Gas Variables ○ Pressure and Mixtures of Gases You will get the most out of the activity if you do the exploration first! The rest of the sections can be worked in any order; you could work on any sections where you want to deepen your conceptual understanding. Part I: Explore the Simulation Take about five minutes to explore the sim. Note at least two relationships that you observe and find interesting. Temperature and Pressure: When you increase the temperature of gas we can see that the pressure also increases as week. This can be explained by the Kinetic Molecular Theory of Gases. Volume and Pressure: As you increase the pressure, we see the volume decrease. It is the same the other way around. This relationship is known as Boyle’s law.

Part II: Kinetic Energy and Speed Sketch and compare the distributions for kinetic energy and speed at two different temperatures in the table below. Record your temperatures (T 1 and T 2 ), set Volume as a Constant Parameter, and use roughly the same number of particles for each experiment (aim for ~100-200). Use the T 2 temperature to examine a mixture of particles. Tips: T 1 = 300 K The Species Information and Energy Histograms tools will help. T 2 = 250 K The system is dynamic so the distributions will fluctuate. Sketch the average or most common distribution that you see. “Heavy” Particles Only “Light” Particles Only Heavy + Light Mixture # of particles (~100-200) 100 100 100+100-200 Kinetic Energy Distribution sketch for T 1 Speed Distribution sketch for T 1 Kinetic Energy Distribution sketch for T 2

Part III: Kinetic Molecular Theory (KMT) of Gases Our fundamental understanding of “ideal” gases makes the following 4 assumptions. Describe how each of these assumptions is (or is not!) represented in the simulation. Assumption of KMT Representation in Simulation 1. Gas particles are separated by relatively large distances. Gas particles are not separated by relatively large distances in the simulation and they enlarge so that it can be seen. 2. Gas molecules are constantly in random motion and undergo elastic collisions (like billiard balls) with each other and the walls of the container. They bounce off of the containers and off of each other. 3. Gas molecules are not attracted or repulsed by each other. They sort of move like balls and have no force from being so close together. 4. The average kinetic energy of gas molecules in a sample is proportional to temperature (in K). The bigger and greater the temperature the faster the particles move.

Part IV: Relationships Between Gas Variables Scientists in the late 1800’s noted relationships between many of the state variables related to gases (pressure, volume, temperature), and the number of gas particles in the sample being studied. They knew that it was easier to study relationships if they varied only two parameters at a time and “fixed” (held constant) the others. Use the simulation to explore these relationships. Variables Constant Parameters Relationship Proportionality (see hint below) pressure, volume Temperature Pressure and volume inversely proportional at constant temp directly proportional or inversely proportional volume, temperature Pressure Volume is directly proportional to the Kelvin temperature at constant pressure directly proportional or inversely proportional volume, number of gas particles Temperature and Pressure Volume and the number of gas particles are directly proportional for a mass of an ideal gas at constant temperature and pressure directly proportional or inversely proportional Hint: A pair of variables is directly proportional when they vary in the same way (one increases and the other also increases). A pair of variables is inversely proportional when they vary in opposite ways (one increases and the other decreases). Label each of your relationships in the table above as directly or inversely proportional.

Pheavy is the pressure contribution from the heavy particles and the pressure contribution from the light particles is known as the Plight. We know that the number of moles and temperature are constant so that allows us to figure out and write out PV=Constant. So for the volume given, we can see that the pressure is directly proportional to the number of moles. So since we have 150 heavy particles and 50 light particles, the heavy particles contribute the 150 out of 200. 2. What is the pressure contribution from the light particles (P light )? How did you figure this out? P light = (0.25) P total This allows us to conclude that the pressure contribution from the light article is 0.25 times the total pressure amount. 3. For each test above, calculate the mole fraction of each gas (number of particles of that type / total particles). Find a relationship between the mole fraction and the pressure contribution of each type of gas. N heavy =X heavy x N total N heavy is gonna be the number of moles of heavy particles, while X heavy is the mole fraction of heavy articles and N total is gonna be the number of total moles. Using gas law we can write P heavy x V = N heavy x RT P heavy x V = N light x RT Since volume and temperature are constant… P heavy = N heavy x RT/V P light = N light x RT/V And when substituting for N heavy and N light ….. P heavy V = X heavy x N total x RT/V P light V = X light x N total x RT/V Lastly P heavy = X heavy x P total P light V = X light x P total 4. The atmosphere is composed of about 78% nitrogen, 21% oxygen, and 1% argon. Typical atmospheric pressure in Boulder, Colorado is about 0.83 atm. What is the pressure contributed by each gas? P total = P nitrogen + P oxygen + P argon P total = 0.83 atm

Mole fraction of nitrogen= 0.78  0.78 x 0.83 atm = 0.6474 atm Mole fraction of oxygen= 0.21  0.21 x 0.83 atm = 0.1743 Mole fraction of argon= 0.01  0.01 x 0.84 atm = 0.0084