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Unit 4 A.11-A.14

Unit 4 A.11-A.14. In which you will learn about: Charles’ Law Gay-Lussac’s Law. Where did A.10 go?. A.10 will be a volume-temperature lab activity and/or pressure-temperature lab activity RANDOM BUT IMPORTANT: STP = standard temperature and pressure (0°C, 1.00 atm).

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Unit 4 A.11-A.14

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  1. Unit 4A.11-A.14 In which you will learn about: Charles’ Law Gay-Lussac’s Law

  2. Where did A.10 go? • A.10 will be a volume-temperature lab activity and/or pressure-temperature lab activity • RANDOM BUT IMPORTANT: • STP = standard temperature and pressure (0°C, 1.00 atm)

  3. A.11 Temperature-Volume Behavior of Gases • This relationship was observed in Activity 2 in our lab when balloons were placed in a warm water bath and an ice water bath. • Increasing or decreasing the temperature produces changes in its volume • Direct relationship, if T increases, so does V and the same is true for a decrease.

  4. History of this Relationship • In the 1780s, French chemists (and hot-air balloonists) Jacques Charles and Joseph Gay-Lussac studied the changes in gas volume cause by temperature changes at constant pressure • Graphs of their data are linear, thus confirming the direct relationship

  5. Absolute Zero • Different gases and different sample sizes produced different lines, BUT they all extended to the same point (absolute zero) • Lord Kelvin used this work of Charles and Gay-Lussac to establish a simple mathematical relationship fore temperature-volume known as Charles’ Law • The Kelvin temperature scale is based off this law

  6. Charles’ Law • Doubling the Kelvin temperature of a gas sample doubles its volume at constant pressure and constant amount of gas. • Lowering temp by half, reduces volume by half, etc. • Charles’ Law:

  7. Kelvin Temperature • For Charles’ Law (and all gas laws involving temperature), temperature must be in Kelvins • K = °C + 273 • Note that it is just K, not °K

  8. A.12 Predicting Gas Behavior: Temperature-Volume(Homework Questions) • What would happen to a balloon’s volume, originally at 20°C, if you took the balloon outdoors in a temperature of 40°C? Assume that pressure is constant and the balloon does not allow any gas to escape. • In planning to administer a gaseous anesthetic to a patient... • Why must the anesthesiologist take into account the fact that during surgery the gaseous anesthetic is used both at room temperature (18°C) and at the patient’s body temperature (37°C)? • What problems might arise if the anesthesiologist did not allow for the patient’s higher body temperature?

  9. A.12 Cont’d 3) An air bubble trapped in bread dough at room temperature (291 K) has a volume of 1.0 mL. The bread bakes in the oven at 623 K (350°C): • Predict whether the air-bubble volume will increase or decrease as the bread bakes. Explain your prediction, using KMT. • Calculate the new volume of the air bubble, using Charles’ law.

  10. A.12 (Last One) 4) You buy a 3.0-L helium balloon in a mall and place it in a car sitting in hot summer sunlight. The temperature in the air-conditioned mall was 22°C, and the temperature inside the closed car is 45°C: • What will you observe happening to the balloon as it sits in the warm car? • What will be the new volume of the balloon? • Sketch two illustrations that depict helium atoms in the balloon, one when the balloon was in the mall and one when it is in the car. • Explain your illustrations, using KMT.

  11. A.13 Temperature-Pressure Behavior of Gases • Picture a closed cylinder of gas, such as a deep-sea scuba tank where volume is constant. • What would happen to the average kinetic energy of gas molecules in the cylinder if you were to heat the tank? • How would this affect the gas pressure?

  12. Answers to “Rhetorical” Questions on Slide 11 • Raising the Kelvin temperature of the gas at constant volume causes an increase in gas pressure (direct relationship) • Increasing temp increases the kinetic energy of the molecules • Because the molecules are moving faster, the number of collisions increases and therefore, pressure increases • Gay-Lussac’s Law:

  13. A.14 Using Gas Relationships(More Homework Questions) Solve the following problems, using appropriate gas relationships: 5) a) If the Kelvin temperature of a gas sample held in a steel tank increases to three times its original value, predict what will happen to the pressure of the gas. Will it increase or decrease? By what factor do you expect the gas pressure to change? b) Draw two molecular models that represent the movement of gas molecules inside the tank at the two temperatures. c) Explain your models, using KMT.

  14. A.14 Cont’d 6) A gas sample at a constant pressure shrinks to one-fourth its initial volume. What must have happened to its temperature? Did it increase or decrease? By what factor did the Kelvin temperature of the gas change? 7) Explain why automobile owners in severe northern climates often add air to their tires in the wintertime and release some air from the same tires in the summertime. 8) Use KMT and gas laws to explain why a weather balloon expands in size as it rises from Earth’s surface. 9) Why does the label on an aerosol container caution you not to dispose of the container in a fire?

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