Student Exploration- Boyle’s Law and Charles’s Law GIZMO

Prior Knowledge Question (Do this BEFORE using the Gizmo.) A small helium tank measures about two feet (60 cm) high. Yet it can fill over 50 balloons! How can such a small tank contain enough helium to fill so many balloons? The tank can hold enough helium because the gas in the tank is under tremendous pressure. Gas will contract under high pressure and expand under low pressure. When the helium goes into the balloons, it occupies much more space because there is less pressure in the balloons than in the tank. Gizmo Warm-up The Boyle’s Law and Charles’ Law GizmoTM shows a container of gas. In the container, the small purple spheres represent molecules. 1. Observe the particles. Are they all moving at the same speed? No, the particles are moving at different speeds. 2. How do the particles interact with the walls and lid of the container? The particles bounce off the walls and lid of the container. These interactions contribute to the pressure on the walls of the container. Pressure is defined as force per unit area. The SI units of pressure are newtons per square meter (N/m2), or pascals (Pa). 3. Slowly drag the temperature (T) slider back and forth. (Note: In this Gizmo, the is used to measure temperature. On the Kelvin scale, 0 degrees is , the coldest possible temperature. Absolute zero is equal to -273.15 °C or -459.67 °F) A. How does the change in temperature affect the speed of the molecules? Molecules move faster. B. How does the change in temperature affect the volume of the container? Volume increases. Kelvin scale Activity A: Boyle’s Law Get the Gizmo ready: Question: How does pressure affect the volume of a gas? 1. Form hypothesis: In this experiment, you will pile weights on the lid of the container of gas. What do you think will happen as more weight is added to the lid? When more weight is added to the lid, I think it will either cause the elements to move faster or slower. Probably slower because the weights will almost cause the container to become smaller. 2. Notice: Look at the DESCRIPTION pane. What is the mass of the lid? 10 kg. How much pressure does the lid exert on the gas? 98.1 3. Collect data: With the temperature held constant at 300 K, use the Select mass slider to place weights on the lid. Record the pressure and volume of the gas for each added mass. Added mass on the lid 0 kg 10 kg 20 kg 30 kg Total mass (lid + added mass) 10 kg 20 kg 30 kg 40 kg Pressure* 98.1 N/m2 196.2 N/m2 294.3 N/m2 392.4 N/m2 Volume 2.54 m3 1.27 m3 0.85 m3 0.64 m3 *This model does not include atmospheric pressure, which is 101,325 N/m2. 4. Analyze: As the pressure increases at constant temperature, what happens to the volume of the gas? As the pressure increases, the volume of the gas decreases. This relationship is called Boyle’s law. 5. Calculate: Compare the pressure and volume values in your data table. A. How did doubling the pressure change the gas volume? Divided by 2. B. How did tripling the pressure change the gas volume? Divided by 3. C. How did quadrupling the pressure change the gas volume? Divided by 4. (Activity A continued on next page) Activity A (continued from previous page) 6. Predict: If the added mass on the lid was 50 kg, a total mass of 60 kg would exert pressure on the gas inside the container. What will be the volume of the gas? .42 7. Test: Test your prediction using the Gizmo. What is the volume of the gas? .42 Was your prediction correct? Yes. 8. Create a graph: On the GRAPH tab, select V vs. P. Set m to 0 kg, and click Record to plot a point on the graph. Plot a point for each possible mass to create a graph showing the relationship between pressure and volume. A. What is the shape of the graph? The shape of the graph is a curve which goes down from left to right. B. How does this graph illustrate Boyle’s law? This graph illustrates Boyle’s law because as pressure increases, the volume of the gas decreases. C. How do you think the graph might change if the temperature was held constant at a higher temperature, say 400 K? It might take longer because the atoms will be moving faster. 9. Apply: Think about a small helium tank that can fill 50 balloons. What must be true about the helium in the tank compared to the helium in the balloons?