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Name_______________ Gas Laws Date___________B____ Scientific laws describe something we have repeatedly _________________ . Usually these laws can be written as simple _____________________ relationships. In physics for example, the relationship “F = m x a” has been _______________ and confirmed so many times that it is called Newton’s ____________ Law and it is part of the Theory of Classical Mechanics. However, laws and ___________ are not the same. A theory does ______ become a law. In fact, a theory is the scientific _________________ behind the laws we observe. The general public often misuses the word “theory” to mean something that “is not yet ____________”. Scientists however, use the word theory with great confidence because it means the best possible explanation based on repeated experimentation. Starting in the ________ and for another 200 hundred years, early chemists were doing experiments on gases and developed many gas laws. At first, there was no “theory” to explain these laws. However, these scientists developed equations that consistently predicted the pressure, volume, and temperature of a gas. Eventually, ______________ (1905) provided experimental evidence for the _______________ _________________ ______________ ____ ___________ . Let’s examine the Kinetic Molecular Theory of Gases: Theoretical Assumption What does this mean for the behavior of gases? 1. Gases particles are very far apart compared to their actual size. 2. Collisions between particles or the walls of containers are elastic 3. Gas particles are in continuous, rapid, random motion 4. There are no forces of attraction between gas particles 5. Temperature is related to average kinetic energy of all the particles in Property Pressure Volume Temperature Definition Standard Units Description 1 Name_______________ Gas Laws Date___________B____ Imagine that you are gas molecule inside a box… If I move faster then I will collide [ more OR less ] with the walls of the container. If the box gets smaller then I will collide [ more OR less ] with the walls of the container. If the box stays the same, but I am colliding with the walls less, I must be moving [ slower OR faster ] If the box gets bigger, but my number of collisions stays the same, I am moving [ slower OR faster ] If my speed and # of collisions stays the same, then the box or volume must be staying the ________ CLASS WORK 1. Describe the difference between a scientific theory and a scientific law? 2. Using the assumptions of Kinetic Molecular Theory, summarize the physical behavior of gases. 3. Using plain language, contrast the 3 main properties (pressure, volume, & temperature) of a gas. 2 Name_______________ Gas Laws Date___________B____ NAME Combined Gas Law Variables that Change? Held Constant? Equation Mathematical Relationship Sketch of Graph CLASS WORK 1. Assume that temperature is held constant. Explain why pressure increases as a gas is compressed into a smaller volume. (Words to use: space, number of collisions, speed) 3 Name_______________ Gas Laws Date___________B____ 2. Assume the volume is held constant. Explain why the pressure of a gas decreases as the temperature of a gas is decreased. (Words to use: space, number of collisions, speed) 3. Assume the pressure is constant. Explain why the temperature of a gas must increase if the volume of a gas increases. (Words to use: space, number of collisions, speed) HOMEWORK 1. Describe each of the following relationships as either “direct” or “inverse”. P & V: ____________ V & T: ____________ P & T: ____________ 2. Make a rough sketch of how Pressure, Volume, and Temperature relate graphically: P vs. V V vs. T P vs. T 3. Finish each statement with “increase” or “decrease” At constant temperature, as the pressure decreases, the volume ________________ At constant pressure, as the volume increases, the temperature ________________ At constant volume, as the temperature decreases, the pressure__________ 4 Name_______________ Gas Laws Date___________B____ Class work (SHOW ALL WORK) Write Boyle’s Law Solve for P1 in terms of the other variables. Rearranged Equation P1 = ____ is constant Write Boyle’s Law Solve for V2 in terms of the other variables. Rearranged Equation V2 = ____ is constant Write Charles’s Law Solve for V1 in terms of the other variables. Rearranged Equation V1 = ____ is constant Write Charles’s Law Solve for T2 in terms of the other variables. Rearranged Equation T2 = ____ is constant Write Gay-Lussac’s Law Solve for P2 in terms of the other variables. Rearranged Equation P2 = ____ is constant Write Gay-Lussac’s Law Solve for T1 in terms of the other variables. Rearranged Equation T1 = ____ is constant 5 Name_______________ Gas Laws Date___________B____ GAS LAW CALCULATION CLASSWORK PRACTICE PROBLEMS *** Warning – Remember that all Temperatures must be in Kelvin*** 1. A sample of oxygen gas has a volume (V1) of 150.0 mL when its pressure (P1) is 0.947 atm. What will the volume (V2) of the gas be at a pressure (P2) of 0.987 atm? The temperature is held constant. Think before you solve… Equation What variable is being held constant? ____ Re-arrange your equation for the unknown This means I need _______________ Law. What variable am I solving for? __________ List Data Solve by plugging in your data P1 = P2 = V1 = V2 = Check your answer = 144 mL 2. A sample of neon gas occupies a volume (V1) of 752 mL at (T1) 25 °C. What volume (V2) will the gas occupy at (T2) 50 °C if the pressure remains constant? Think before you solve… Equation What variable is being held constant? _____ This means I need ________________ Law. Re-arrange your equation for the unknown (You’ll need to cross-multiply ) What variable am I solving for? __________ List Data Solve by plugging in your data V1 = V2 = T1 = T2 = Remember to convert to: K = °C + 273 Check your answer = 815 mL 6 Name_______________ Gas Laws Date___________B____ 3. At constant pressure, a sample of Neon gas has a volume of 3.0 L after being heated from 25 °C to 100 °C. What was the original volume? Think before you solve… Equation What variable is being held constant? ____ This means I need ___________ Law. What variable am I solving for? ______ * Hint – looking for the “original” volume List Data Remember to convert to: K = °C + 273 Solve Answer = 2.40 L 4. A balloon filled with helium gas has a volume of 500 mL at a pressure of 1 atm. The balloon is released and reaches an altitude of 6.5 km, where the pressure is 0.5 atm. If the temperature remains the same, what volume does the gas occupy at this height? Think before you solve… Equation What variable is being held constant? ____ This means I need ___________ Law. What variable am I solving for? ______ List Data Solve Answer = 1000 mL 7 Name_______________ Gas Laws Date___________B____ GAS LAW CALCULATION HOMEWORK PROBLEMS *** Warning –All Temperatures must be in Kelvin: K = C +273*** Use the relationship between pressure and volume to solve for the missing value. P 1 = 4 atm, V1 = 200.0 mL, and P2 = 8 atm. What does V2 equal? List data Equation Solve (estimate & check units) Solve for unknown variable. Ans. 100 mL 1. Use the relationship between volume and temperature to solve for the missing value. V 1 = 100.0 mL, T1 = 25 °C, T2 = 50 °C, V2 = ? Convert Temperatures to Kelvin first! List data Equation Solve (estimate & check units) Ans. 108.4 mL 2. Use the relationship between pressure and temperature to solve for the missing value. P 1 = 1 atm T1 = 200 °C, P2 = 2 atm, T2 = ? Convert Temperatures to Kelvin first! List data Equation Solve (estimate & check units) Ans. 946 K 8 Gas Laws Name_______________ Date___________B____ MORE GAS LAW CALCULATION PROBLEMS *** Warning – Remember that all Temperatures must be in Kelvin*** 1. A sample of oxygen gas has a volume of 250.0 mL when its pressure is 1.03 atm. What will the volume of the gas be at a pressure of 1.14 atm if the temperature remains constant? Ans = 226 mL 2. A sample of neon gas occupies a volume of 752 mL at 25 °C. What volume will the gas occupy at 50 °C if the pressure remains constant? Ans. = 815 mL 3. The gas in a container is at a pressure of 3.0 atm at 25 °C. Directions on the container warn the user not to keep it in a place where the temperature exceeds 52 °C. What would the pressure in the container be at 52 °C? Ans. = 3.27 atm 9 Gas Laws Name_______________ Date___________B____ 4. A sample of Neon gas has a volume of 2 L after being heated from 30 °C to 100 °C. What was the original volume? Ans. = 1.62 L 5. A balloon filled with helium gas has a volume of 500 mL at a pressure of 1 atm. The balloon is released and reaches an altitude of 13 km, where the pressure is 0.1 atm. If the temperature remains the same, what volume does the gas occupy at this height? Ans. = 5000 mL 6. A sample of Argon gas has final temperature of 40 °C after being pressurized from 1.20 atm to 2.00 atm. What was the initial temperature of the gas? Ans. = 188 K 10