Créer une présentation
Télécharger la présentation

Télécharger la présentation
## The Nature of Gases

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -

**The Nature of Gases**• Gas Pressure –the force exerted by a gas per unit surface area of an object • Due to: a) force of collisions b) number of collisions**The Nature of Gases**• The SI unit of pressure is the pascal (Pa) • Other units: • millimeters of mercury (mm Hg) • torr (torr) • atmospheres (atm)**The Nature of Gases**• Conversions between pressure… 1 atm = 760 mmHg = 760 torr = 101,325 Pa • Convert the following measurement into mmHg, 596 torr. • Convert your answer for number 1 into atm.**Temperature Conversions**• Temperature is measured in… • Kelvin • Conversion Factor: • C = K – 273 • K = C + 273**The Nature of Gases**• Standards!! • temperature of 0oC (273K) • pressure of 1 atm • This is called Standard Temperature and Pressure, or STP**The Gas Laws are mathematical**• The gas laws will describe HOW gases behave.**Boyle’s Law**Relates Pressure and Volume they are inversely related at constant temperature. P1 V1 = P2 V2 T = constant**Boyle’s Law**When the volume goes up, the pressure goes down V P (at constant T)**Charles’ Law**• The volume is directly to the temperature, with constant pressure.**Charles’ Law**• As one goes up so does the other.**Gay-Lussac’s Law**• At constant volume, pressure and temperature are directly related. V = constant**Gay-Lussac’s Law**As one goes up so does the other.**The Combined Gas Law**The combined gas law is between pressure, volume and temperature.**If the temperature remains constant...**x P1 P2 V1 x V2 = T1 T2 Boyle’s Law**If the pressure remains constant...**P1 V1 P2 x V2 x = T1 T2 Charles’s Law**If the volume remains constant...**P1 V1 P2 x V2 x = T2 T1 Gay-Lussac’s Law**Lab**Describe what is happening What variables are being observed? Which Gas Law/s does it represent?**Gas Law Problems**• Create 3 Gas Law problems • Give the proper information needed to solve • Do not tell which Gas Law it is. Create an answer key telling which Gas Law it is and how to solve. • Switch problems with a partner and solve each problem; tell what law each problem is and how to solve it. • Once you have solved all problems switch back and check each others answers.**Ideal Gas Law**PV = nRT R is the ideal gas constant. R = 0.0821 L atm/ mol K Tells you about a gas NOW. The other laws tell you about a gas WHEN IT CHANGES.**Ideal Gas Law**Using this equation (PV = nRT) we can rearrange it to solve for P, V, n and T. Try to rearrange the equation to solve for P, V, n and T. • Did you get… P = nRT / V V = nRT / P n = PV / RT T = PV / nR**Dalton’s Law of Partial Pressures**States that the total pressure of a mixture of gases is equal to the sum of the pressures of all the gases. PTotal = P1 + P2 + P3 + . . .**Dalton’s Law of Partial Pressures**• Example: A mixture of oxygen gas, carbon dioxide gas, and nitrogen gas has a total pressure of 0.97 atm. What is the partial pressure of oxygen gas, if the partial pressure of carbon dioxide if 0.70 atm and nitrogen is 0.12 atm?**DLPP-PP**1.Find the total pressure of a mixture that contains three gases with the following partial pressures: 6.6 kPa, 3.2 kPa, and 1.2 kPa. 2. Find the total pressure of a mixture that contains five gases with the following partial pressures: 7.81 kPa, 13.20 kPa, 2.43 kPa, 12.50 kPa, and 2500 Pa. 3. Find the partial pressure of ammonia in a mixture of three gases with a total pressure of 75.6 kPa if the sum of the partial pressures of the other two gases is 34.9 kPa.**Practice Problems**A cylinder of argon gas contains 50.0 L of Ar at 18.4 atm and 127 °C. How many moles of argon are in the cylinder? A 283.3-g sample of X2(g) has a volume of 30 L at 3.2 atm and 27 °C. What is element X?**Practice Problems**An ideal gas sample is confined to 3.0 L and kept at 27 °C. If the temperature is raised to 77 °C and the initial pressure was 1500 mmHg, what is the final pressure?**Practice Problems**A sample of helium was compressed at 35 °C from a volume of 0.5 L to 0.25 L where the pressure is 500 mmHg. What was the original pressure?**Practice Problems**A hot air balloonist puts 125,000 Liters of air into their balloon at 27 °C and atmospheric pressure. When they heat the air to 200 °C at constant pressure, what is the final volume of the air in the balloon?**Get with your lab partners**Using paper, glue, etc… demonstrate the Gas Law assigned to your group. You may construct something, draw something, or create a poster. Your project must include an experiment in which you test your Gas Law properties. You have 45 minutes before you have to present your ideas to the class.**The Nature of Gases**• Kinetic refers to motion • The kinetic-molecular theory describes the behavior of gases in terms of particles in motion!**The Nature of Gases**• Three basic assumptions of the kinetic theory as it applies to gases: #1. Particle Size: Gases are composed of particles- • Small, hard spheres • Insignificant volume; relatively far apart from each other • No attraction or repulsion between particles**The Nature of Gases**#2. Particle Motion: Particles in a gas move rapidly in constant random motion • Move in straight paths, changing direction only when colliding with one another or other objects**The Nature of Gases**#3. Particle Energy: Collisions are perfectly elastic- meaning… • kinetic energy is transferred without loss**Phase Changes 13.4**• Prepare a Poster on Phase Changes • Include all important information for each portion *See handout • You may explain your information as your group sees fit. • After 30 min you will present to the class