G9 Elite Science Lab Assessment Gas properties and Kinetic Molecular Theory (KMT) https://phet.colorado.edu/en/simulation/gas-properties Purpose: To determine the relationship and observe how changes in parameters affect the behavior of gas particles. Background information: The behavior of Ideal gases can be understood knowing the pressure, volume, temperature and number of moles of the gas and how these parameters are interrelated. These properties can be experimentally measured in the laboratory. The kinetic molecular model for an ideal gas described a view of the behavior of gas particles at the atomic/particulate level. In this virtual lab you will observe the behavior of gases when different variables are changed. The variables that you will change and measure are temperature, pressure and volume. Pre-Lab Questions (5 points) 1. State two postulates of Kinetic molecular theory (KMT) you may not state the one mentioned in question 2 red font: 1. They experience no significant attractive or repulsive forces 2. Two factors determine the kinetic energy of a particle which are mass and velocity [1] 2. According the KMT, “collisions between particles are perfectly elastic”. What does that mean? There would be no lost energy because the kinetic energy gets transferred between the colliding particles [1] 3. Explain why a helium filled balloon “shrinks” when it is taken from a warm room to the outside on a cold day. (Assume that atmospheric pressure is the same inside the warm room as outside!) [3] Due to the gas within cooling off due to the low temperature, the balloon's volume shrinks. The helium balloon rises because, at room temperature, it is lighter than air with the same volume of air. Procedure, Part A: (4 points) 1. Open the simulation on the PhET website by clicking the link below: https://phet.colorado.edu/en/simulation/gas-properties 2. Once the link opens, you will have the image below: 3. Click the white middle play button, the image below will appear, then click on “ideal” 4. Click on “Ideal” and make sure the Constant Parameter (hold constant) button is set to nothing. 5. Click on particles to pump 50 heavy gas molecules and 50 light gas molecules in the gas container. How do the velocities of the heavy gas molecules compare to those of the light gas molecules? [1] The heavy molecules move slower than the light molecules 6. Use the Heat Control to add heat (500K). Notice that the thermometer shows an increasing temperature. What happens to the velocities of the gas molecules? [1] The molecules move faster the higher the heat is 7. Now, use the Heat Control to remove energy (100K). What happens to the velocities of the gas molecules? [1] The molecules started to move slower with the decreasing of the heat 8. With evidence, state the effect of steps 6 and 7 on the pressure of the gas in the gas container. [1] In step 6 because the heat is higher there is more pressure and in step 7 the pressure decreases with the decrease of the temperature. Part B: (3 points) 1. Reset the system by clicking this button 2. Add 250 light molecules, then set the Constant Parameter (hold constant) button to Volume 3. Record the temperature and pressure range of the system [1] Temperature = 300k and pressure range= 28.9 – 29.2 4. Remove heat (50K) from the system using the Heat Control. What happens to the pressure and why? [1] The pressure decreases. The molecules of a gas receive more energy when heated, causing them to move more quickly. This results in increased pressure and more impacts on the container's walls. 5. State the relationship between temperature and pressure? [1] According to the kinetic theory of gases, the relationship between the kinetic energy of the molecules 𝑃1 𝑃 of a gas and the absolute temperature is proportional = 2. 𝑇1 𝑇2 Part C: (3 points) 1. Reset the system by clicking this button 2. Add 250 light molecules then set the Constant Parameter (hold constant) button to Pressure 3. Add heat to the system using the Heat Control. What happens to the volume of the gas container and why? [1] Once heat is added the volume increases. 4. State and write the mathematical equation for the relationship between temperature and volume [1] Directly probational Part D: (4 points) 1. Reset the system by clicking this button 2. Add 250 light molecules then set the Constant Parameter button to Temperature 3. Record the pressure range of the system [1] 28.9 – 29.4 4. Move the Vertical Lid so that the volume of the gas container is approximately half 5. Record and explain in terms of KMT the effect of step 4 on the system [2] 52.7 – 53.4 Because pressure and volume are inversely proportional when the volume decreases and the pressure increases 6. State and write the mathematical equation for this relationship [1] PV = nRT 1 𝑃 ∝ 𝑉 Application Questions: (6 points) In terms of Kinetic Molecular Theory (KMT), answer the following questions: 4. You notice that one of your tires seems a little flat one morning, and decide to fill it with air at a gas station. By the time you get to the gas station it looks fine, and the pressure is normal. Explain what has happened to the air in the tire? [2] Low temperatures in the morning cause the air to condense. Because of this, the tire's air occupies less volume and loses pressure. In the morning, the tire appeared to be flat. 5. The largest container on popcorn on record was 106 m3. There is water vapor (a gas) inside popcorn kernels. Why does adding heat pop the kernel into corn? [2] The kernel of popcorn contains some amount of water in the form of gas. As the temperature inside a container inside the container increases, the water starts to expand, and hence the pressure continues to increase inside the starch layer of the kernel. 6. Why is it dangerous to throw aerosol containers either full or empty (like hair spray cans) into a fire? [2] Because they could explode and the propellant within might be flammable Total Score 25points 100 %
