Behavior of Gases Chapter 10 & 12
Laws versus Theories • Scientific Law • A law is a statement that describesactions or a set of actions that occurs consistently. • Example: Law of Conservation of Mass • Scientific Theory • A theory is a model that explains why experiments give certain results. • Example: Kinetic Molecular Theory
Postulates of the Kinetic Molecular Theory of Gases • All gases particles are in constant and random motion. • There are no sources of attractions or repulsion among gas particles. • The collision of these gas particles with an object results in gas pressure. • The average kinetic energy of these gas particles is directly related to their absolute temperature.
Kinetic Molecular Theory Experiment Chemical Reactions HCl(aq) + NaHSO3(aq) SO2(g) + NaCl(aq) + H2O(l) AND NaOH(aq) + NH4Cl(aq) NaCl(aq) + H2O(l) + NH3(g)
Kinetic Molecular Theory Experiment • BTB • Acidic Solutions: Red orYellow/Orange • Basic Solutions: Blue orPurple • Safety • Wear your safety goggles!
Explanation of Kinetic Molecular Theory Experiment Postulate #1 & 2 The universal indicator changed colors in every direction because gas particles are in constant and random motion, which means the gas should go in every direction.
Crushing Can Postulate #3 & 4 • As the water boils, the can becomes full of steam. • When the can is inverted into the cold water bath, the temperature of the gas inside the can drops and some of the water condenses. • Since the temperature drops and there are fewer gas particles, the pressure inside the can decreases. • Since the pressure outside the can is now much greater, this higher pressure crushes the can.
Squirt Bottle Postulate #3 • Dry ice is changing from a solid to a gas. This creates more gas particles inside the water bottle. • Since there are more gas particles, there will be more collisions of gas particles with the walls of the container. • Since there are more collisions of gas particles with the walls of the container, the pressure inside the bottle increases. • The higher pressure pushes the water up and out of the water bottle. (Remember pressure is a force, which is a push or a pull!)
Candles in a Beaker • I want you to record • your observations. • explain why your observations are occurring using the kinetic molecular theory. • Wear safety goggles!
Candles in a Beaker Postulate #3 & 4 • When the candles go out, the temperature begins to drop. • The gas particles slow down, which causes the pressure inside the beaker to drop. • The higher pressure on the outside of the beaker pushes the water into the beaker.
Pressure • What is pressure? A Force Exerted by a Gas over a Given Area • What causes pressure? Collisions of the Gas Particles with the Walls of the Container That’s Pressure! Walls of the Container Gas Particle
Units of Pressure atmospheres = atm millimeters of mercury = mmHg kilopascals = kPa pounds per square inch = psi 1 atm = 760mmHg = 101.3kPa = 14.7psi
Sample Problem #1 How many kilopascals are equivalent to 880mmHg?
Sample Problem #2 Calculate the number of psi that are in 2.60atm.
Homework • Complete pg. 5 in your booklet.
Charles’s Law Temperature must be in Kelvin.
On the Back of Your Index Card Summarize Charles’s Law in a single, complete sentence.
Example Problems • The temperature of a 0.65L sample of carbon dioxide gas is 580K. If the pressure remains constant, what is the new volume of the gas if the temperature increases to 1300K? • A balloon has a volume of 5.6L at a temperature of 98oC. If the volume of balloon increases to 9.5L, what will be the temperature of the gas in Celsius? Assume that the pressure remains constant.
Gay-Lussac’s Law Temperature must be in Kelvin.
On the Back of Your Index Card Summarize Gay-Lussac’s Law in a single, complete sentence.
Example Problem A certain gas has a pressure of 56.0kPa at a temperature of 56.1oC. If the volume remains constant, what would be the new pressure if the temperature was increased to 78.2oC?
Homework Complete pg. 10 & 12 in your booklet.
On the Back of Your Index Card Summarize Boyle’s Law in a single, complete sentence.
Example Problems • The pressure of a 3.5L balloon was determined to be 1.5atm. Assuming that the temperature remained constant, what would be the volume of the balloon if the pressure was decreased to 0.45atm? • At 45oC, a certain container of gas has the volume of 580mL and a pressure of 980mmHg. What would be the new volume of the gas at 250 mmHg and 45oC?
Homework Complete pg. 14 in your booklet.
Combined Gas Law Temperature must be in Kelvin. Remember STP = 1 atm and 0oC
Example Problems • A hot air balloon has a volume of 7500L at 270K and a pressure of 1.2atm. What will be the volume of the balloon if the pressure changed to 0.90atm and the temperature decreases to 230K? • The volume of a gas at STP is 22.4L. At 12oC, the volume of the balloon changes to 55.0L. What is the new pressure?
Dalton’s Law of Partial Pressures + = A partial pressure is the pressure a gas would have or would exert if it were alone in the container.
Example Problems • Air contains oxygen, nitrogen, carbon dioxide, and trace amounts of other gases. What is the partial pressure of oxygen (Poxygen) at 101.3kPa if the partial pressures of nitrogen, carbon dioxide, and other gases are 79.10kPa, 0.040kPa, and 0.94kPa, respectively? • A mixture of gases contains oxygen, nitrogen, and helium. The partial pressure of oxygen is 2.1atm. The partial pressure of nitrogen in 0.21atm, and the partial pressure of helium is 7.80atm. Determine the total pressure of this mixture.
Ideal Gas LawDescribing the Behavior of Ideal Gases P V = n R T P = pressure V = volume in LITERS n = moles R = gas constant T = temperature in KELVIN The value of R that you use is based on your units of pressure. R = 0.08206 or 62.4 or 8.314
Ideal Gases • We assume that all gases behave ideally. • Most gases are not 100% ideal. • Gases tend to be the most ideal at high temperatures and low pressures!
Example Problems • A 5.60 L sample of an ideal gas contains 0.954 moles at 742 mmHg. Calculate the temperature. • What volume is occupied by 19.6g of methane, CH4, at 27oC and 1.59atm? • What mass of 2250mL chlorine gas at 45oC and 120kPa? Don’t forget about your diatomic elements! H2, N2, O2, F2, Cl2, Br2, I2
Tips for the Ideal Gas Law Problems with Stoichiometry • The volume will always need to be in liters and the temperature in Kelvin. • Always have a balanced chemical equation! • You can only use 22.4 L = 1 mol at STP. • For most problems, you will do one of two ways. • Solving for Volume: You will use stoichiometry to solve for moles and then use the ideal gas law to solve for volume. • Solving for Moles or Mass: You will use the ideal gas law to solve for moles and then use stoichiometry to solve for moles or mass.
More Challenging Gas Law Problems • Nitrogen and hydrogen gases react to produce ammonia. Determine the mass of ammonia that would be produce if you reacted 4.0L of nitrogen gas at 298K and 1.5 atm. • Water decomposes to form oxygen and hydrogen. If 3.4g of water decomposes, what volume of oxygen gas would be formed at 56oC and 2.3 atm?