1. GASES Unit 10

2. KINETIC-MOLECULAR THEORY OF GASES 1.Gases consist of tiny atoms or molecules that are in constant random motion. 2.The space between gas molecules is very large compared to the actual size of a molecule/atom of gas. 3.Gas molecules collide with each other and the sides of the container that holds them.

3. KINETIC-MOLECULAR THEORY OF GASES 4. Collisions with other gas particles are completely elastic and result in no net change in kinetic energy. 5. Collisions with the sides of the container result in the creation of force per unit area of a surface =pressure. Pressure exerted by a gas is the result of the collisions of gas molecules against the walls of its container.

4. Atmospheric Pressure Pressure exerted on objects on surface of earth by the atmospheric gases in response to gravity

5. Atmospheric Pressure STP -Standard Temperature (0 ⁰ C) & Atmospheric Pressure (1.00 atm)

6. How does elevation affect atmospheric pressure? High elevations = less atmospheric pressure (less dense air exerts less pressure) Low elevations = greater atmospheric pressure (atmosphere is denser as you move closer to the earth’s surface)

7. UNITS OF PRESSURE atm = atmospheric pressure mmHg = millimeters of mercury Pa = pascals kPa = kilopascals torr = Torr

8. Pressure Conversions 1 atm = 760 mmHg 1 atm = 760 torr 1 atm = 101.3 kPa 1 atm = 101,325 Pa 1atm = 14.70 psi (lb/in 2) So, 1 atm = 760 mmHg = 760 torr = 101.3 kPa = 14.70 psi

9. Pressure Conversions Convert 3.2 atm into mmHg Convert 99.7 kPa into mmHg

10. How is pressure measured? Barometer = an instrument that measures atmospheric pressure (unit = mmHg). Manometer = instrument that measures the pressure of a confined (trapped) gas against atmospheric pressure.

11. Manometer problems An open manometer is filled with mercury and attached to a container of methane gas. The mercury level is 45 mm higher in the arm connected to the methane gas. What is the pressure of the methane gas if the atmospheric pressure is 740mmHg?

12. Properties of Gases are fluids = any substance that can flow have low density are highly compressible completely fill a container have mass exert pressure move through each other rapidly pressure depends on the temperature

13. Measureable Properties of Gases P = pressure exerted by gas V = volume (L) occupied by the gas T = temperature (K) of the gas n = number of moles of the gas

14. Boyle’s Law P 1 V 1 = P 2 V 2 When the temperature and the amount of gas is constant, the pressure & volume have an indirect relationship. if V increases, the P decreases if V decreases, the P increases

15. Boyle’s Law problems A sample of neon to be used in a neon sign has a volume of 1.51 L at a pressure of 635 torr. Calculate the volume of the gas after it is pumped into the tubes of the sign, where it shows a new pressure of 785 torr.

16. Boyle’s Law problems In an automobile engine the gaseous fuel-air mixture enters the cylinder and is compressed by a moving piston before it is ignited. In a certain engine the initial cylinder volume is 0.725 L. After the piston moves up, the volume is 0.075 L. The fuel-air mixture initially has a pressure of 1.00 atm. Calculate the pressure of the compressed fuel-air mixture.

17. Charles’s Law V 1 = V 2 T 1 T 2 When the pressure and amount of gas are constant, temperature and volume have a direct relationship: if V increases, T increases if V decreases, T decreases **Temperature must be in Kelvin (ºC + 273 = K)

18. Charles’ Law Problems If 1,235mL of nitrogen gas is placed in a sealed container at a temperature of 57°C, what will its volume (in liters) be when the temperature of the gas reaches 150°C?

19. Charles’ Law Problems In former times, gas volume was used as a way to measure temperature using devices called gas thermometers. Consider a gas that has a volume of 0.675 L at 35˚C. What is the temperature (in ˚C) of a room where this gas has a volume of 0.535 L?

20. Avogadro’s Law When pressure and temperature are constant, volume & the number of moles have a direct relationship if V increases, moles increases if V decreases, moles decreases (V = litersn = moles)

21. Avogadro’s Law If 0.105mol of helium gas occupies a volume of 2.35L at a certain temperature & pressure, what volume would 0.432mol of helium occupy under the same conditions?

22. Gay-Lussac’s Law When the volume and amount of gas are constant, the pressure and temperature have a direct relationship: if P increases, T increases if P decreases, T decreases (P= same unitT = Kelvin)

23. Gay-Lussac’s Law A can of gas is at 30. kPa and 20°C. What is its pressure at 48°C ?

24. Gay-Lussac’s Law The same sample of nitrogen as in the previous problem starts at 122˚C and 1.07 atm. After cooling the pressure is measured to be 0.880 atm. What is the new temperature is K and ˚C?

25. Combined Gas Law Combination of Boyle’s, Charles’s, & Gay-Lussac’s (Moles are constant) P = same unit V = liters or milliliters T = Kelvin

26. Combined Gas Law A sample of methane gas that has a volume of 3.8L at 8°C and 362kPa is heated to 84°C and the pressure is raised to 573kPa. Calculate its new volume.

27. Ideal Gas Law PV = nRT *R is the universal gas constant P must be in atm V must be in Liters R = 0.08206 T must be in Kelvin n must be in moles

28. Ideal Gas Law A balloon contains 1.10 mol of helium and has a volume of 2.70 L at 1.00 atm. Calculate the temperature of the helium in the balloon in Kelvin and °C.

29. Ideal Gas Law What volume is occupied by 0.250 mol of carbon dioxide gas at 25˚C and 371 torr?

30. Ideal Gas Law Radon, a radioactive gas formed naturally in the soil, can cause lung cancer. It can pose a hazard to humans by seeping into houses and there is concern about this problem in many areas. A 1.5 mol sample of radon gas has a volume of 21.0 L at 33˚C. What is the pressure of this gas?

31. Dalton’s Law of Partial Pressures Each gas in a mixture creates pressure as if the other gases were not present. The total pressure is the sum of the pressures created by the gases in the mixture The pressure each gas exerts in the mixture is called its partial pressure P total = P 1 + P 2 + P 3 + P 4…

32. Dalton’s Law of Partial Pressures

33. Dalton’s Law problem A mixture of neon and argon gases exert a total pressure of 2.39atm. The partial pressure of neon alone is 1.84atm. What is the partial pressure of argon gas?