Quiz on Homework 10 and 11 A manometer is used to measure gas pressure. Gas molecules bounce against the sides of the container, Pressure = Force/Area therefore, the more collisions, the more pressure. • For what purpose is a manometer used? • Explain how a gas exerts pressure on its container. • Which gas exerts less pressure, the one on the right or the left? • What is the value of standard atmospheric pressure in kPa. • If the difference in height in the manometer on the left is 75mm, and atmospheric pressure is 100 kPa, what is the pressure of the gas in the left manometer? The gas on the left exerts less pressure 101.3 kPa Pgas = 100 – 75/7.5 Pgas = 90 kPa
Patm – h/7.5 Patm + h/7.5 Due: HW 11: Define and draw a labeled diagram of a manometer and a barometer. Take notes on page 381 sample problem; Do #1-8 page 382 Due: HW #12: Do #25 28 and 40 page 390 and 391. If you have trouble deciding when to add, and when to subtract atmospheric pressure, first draw a sketch of the manometer. Add atmospheric pressure if gas pushes more than atmosphere. Due: HW #13 Notes page 384 385; Do #29, 30 page 391 Due Tomorrow: HW 14 # 32,33,34 page 391 Due Wednesday: HW 15: Notes page 385; Do # 16 p 388; #35,43 page 391 Extra Credit: #44,45,46, 48,49,50 page 392 (20 pts) (label it HW #16) Whatever is not done in class is due Friday, April 30. HW 14 Due Tuesday, Test Wed.
How do you solve these problems? • An open manometer, such as the one in figure 15.4, is filled with mercury and connected to a container of hydrogen. The mercury level is 62 mm higher in the arm of the tube connected to the gas. Use this model ( Patm - ht/7.5) kPa Atmospheric pressure is 97.7 kPa. What is the pressure of the hydrogen in kilo pascals? Patm – ht/7.5 97.7kPa – (62mm/7.5kPa/mm) = 97.7 kPa – 8.3 kPa = 89.4 kPa
Temperature and Heat • Temperature is the average kinetic energy of molecules. • Absolute zero is -273.15oC, -273oC. • To convert from Celsius to Kelvin add 273 • To convert to Celsius subtract 273. • One Celsius degree = 1 Kelvin degree!
9. a. 86K b. 191 K c. 533 K d. 321 K e. 894 K = -187oC = - 82oC = 260oC = 48oC = 621oC Do #9- 12 in class - 273K - 273K - 273K 11 a. 559oC b. 417 oC c. 111oC d. -253 oC e. – 213 oC 12. N2 = 28g/mole F2 = 38 g/mole CO2 = 44g/mole O2 = 32 g/mole - 273K - 273K 10. a. 23oC b. 58oC c. -90oC d. 18oC e. 25oC + 273K = 296 K + 273K = 331 K + 273K = 183 K N2 moves the fastest because it weighs the least. + 273K = 291 K + 273K = 298 K
States of matter most movement Gases form when atoms do not have enough attractive force to stay near each other. Gases move rapidly filling the entire container. least movement Solids are organized structures with lots of attraction and little “freedom” to move Liquids consist of disorganized atoms/molecules which are attracted to each other.
How do you solve problems with closed end manometers or barometers? 2. A closed manometer, like the one in figure 15.4, is filled with mercury and connected to a container of nitrogen. The difference in the height of mercury in the two arms is 691 mm. What is the pressure of the nitrogen in kilopascals? 691 mm/ 7.5 mm/kPa Since the “other side” has a pressure of zero, adding or subtracting changes nothing! Pnitrogen = 92.1 kPa
How do you solve these problems? 3. An open manometer connected to a tank of argon has a mercury level 38 mm higher in the atmospheric arm. Use this model ( Patm + ht/7.5) kPa If Atmospheric pressure is 96.3 kPa, what is the pressure of Argon in kPa? Patm + ht/7.5 96.3kPa + (38mm/7.5kPa/mm) = 96.3 kPa – 5.1 kPa = 101.4 kPa
Answers to homework • page 382 1-8 (1/2 credit if the work is not shown) 1. 89.4 kPa 2. 92.1 kPa 3. 101.4 kPa 4. 11.5 kPa 5. All matter is composed of small particles; these particles are in constant motion; all collisions between particles are perfectly elastic. 6. Gas molecules collide with the walls of the container holding the gas, and each collision exerts a force on the container. The force of collision and the number of collisions cause pressure. 7. In an open-arm manometer one arm of the U-tube is open to the atmosphere. The gas being studied exerts pressure on the other arm. In a closed-arm manometer, there is a vacuum above the liquid in one arm. If a closed-arm manometer is used to measure atmospheric pressure, it is called a barometer. An open-arm manometer measures the difference in pressure between the atmosphere and the gas sample. A closed-arm manometer measures pressure independently of atmospheric pressure. 8. 16.0 kPa; 10.7 kPa
# 27. An open manometer like the one in figure 15.4 is used to measure the pressure of a gas sample. The mercury level is 24 mm higher in the arm open to the atmosphere What is the pressure, in kilopascals,of the gas in the container if the air pressure is 100.3 kilopascals? • Patm = 100.3 + 24/7.5 • Patm = 103.5kPa
# 26. In a closed manometer, assume that the height of the levels differs by 522 mm Hg. What is the pressure, in kilopascals, of the gas in the container? • Pgas = 522/7.5 • Pgas = 69.6 kPa Answers to the rest of the questions are: 27. 103.5 kPa 28. 106.7 kPa 29. The temperature increases directly (proportionally) with an increase in Kinetic energy. 30. Absolute zero means all molecular motion ceases (stops). Homework where work is shown only merits ½ credit!