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# Lecture 14.2b- Gas Law Equations

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Section 14.2 lecture (part B) for Honors & Prep Chemistry

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• The pressure of a gas changes as the volume changes. INTERPRETING GRAPHS a. Observing When the volume is 2.0 L, what is the pressure? b. Predicting What would the pressure be if the volume were increased to 3.0 L? c. Drawing Conclusions Based on the shape of the graph, describe the general pressure-volume relationship.
• This graph shows how the volume changes as the temperature of a gas changes. INTERPRETING GRAPHS a. Observing What is the unit of temperature? b. Drawing Conclusions What happens to the volume as the temperature rises? c. Predicting If the temperature of a gas were 0 K, what would the volume of the gas be?
• ### Lecture 14.2b- Gas Law Equations

1. 1. <ul><li>Bellwork- Gas Variables </li></ul><ul><li>What four variables are needed to describe a gas sample? </li></ul><ul><li>What units are they measured in? </li></ul><ul><li>Do you need to know what kind of gas it is? </li></ul>
2. 2. The combined gas law Uses three gas variables to describe a gas sample at two different times. If a variable does not change (is constant) it can be removed from the equation. P 1 V 1 P 2 V 2 T 1 T 2 =
3. 3. Boyle’s Law: Pressure and Volume <ul><ul><li>If the temperature is constant, as the pressure of a gas increases, the volume decreases. </li></ul></ul><ul><ul><li>LAW - P  , V  </li></ul></ul><ul><ul><li>Constants- amount of gas, Temp </li></ul></ul>P 1 V 1 P 2 V 2 T 1 T 2 = P 1 V 1 P 2 V 2 =
4. 4. <ul><ul><ul><li>Boyle’s law states that for a given mass of gas at constant temperature, the volume of the gas varies inversely with pressure. </li></ul></ul></ul><ul><ul><ul><li>Only if T and n are held constant </li></ul></ul></ul>
5. 5. INDIRECTLY PROPORTIONAL aka INVERSELY PROPORTIONAL
6. 6. Boyle Problem V 1 = 30.0L All math examples should be in your notes L measures Volume(V)
7. 7. Boyle Problem V 1 = 30.0L V 2 = ? P 1 = 103 kPa P 2 = 25.0 kPa kPa measures Pressure(P)
8. 8. Boyle Problem V 1 = 30.0L V 2 = ? P 1 = 103 kPa P 2 = 25.0 kPa These two values go together because they describe the gas at the same moment.
9. 9. Boyle Problem V 1 = 30.0L V 2 = ? P 1 = 103 kPa This is the unknown
10. 10. Boyle Problem V 1 = 30.0L V 2 = ? P 1 = 103 kPa P 2 = 25.0 kPa This is a pressure value
11. 11. Boyle Problem V 1 = 30.0L V 2 = ? P 1 = 103 kPa P 2 = 25.0 kPa These two values go together because they describe the gas at the same moment.
12. 12. Boyle Problem Temp is constant and I need an equation that relates pressure and volume. P 1 V 1 = P 2 V 2 V 1 = 30.0L V 2 = ? P 1 = 103 kPa P 2 = 25.0 kPa P 1 V 1 = P 2 V 2 T 1 T 2
13. 13. Boyle Problem P 1 V 1 = P 2 V 2 103 kPa x 30L = 25.0 kPa x V 2 ___________ ___________ 25.0 kPa 25.0kPa = 124 L P  ,V  GOOD! V 1 = 30.0L V 2 = ? P 1 = 103 kPa P 2 = 25.0 kPa
14. 14. for Sample Problem 14.1
15. 15. <ul><li>Charles’s Law: Temperature and Volume </li></ul><ul><ul><ul><ul><li>As the temperature of an enclosed gas increases, the volume increases, if the pressure is constant. </li></ul></ul></ul></ul><ul><ul><ul><ul><li>LAW- T  ,V  </li></ul></ul></ul></ul><ul><ul><li>Constants- moles of gas, Pressure </li></ul></ul>P 1 V 1 P 2 V 2 T 1 T 2 = V 1 V 2 T 1 T 2 =
16. 16. <ul><ul><ul><li>Charles’s law states that the volume of a fixed mass of gas is directly proportional to its Kelvin temperature </li></ul></ul></ul><ul><ul><ul><li>if the pressure is kept constant. </li></ul></ul></ul>
17. 17. DIRECTLY PROPORTIONAL
18. 18. 14.2 T 1 = 24  C T 2 = 58  C V 1 = 4.00L V 2 = ? T must be in Kelvins!! + 273 = 297K + 273 = 331K V 2 = 4L  297K x 331K = 4.46 L T  V  GOOD! 4.00L V 2 297 K 331 K =
19. 19. for Sample Problem 14.2
20. 20. <ul><li>Gay-Lussac’s Law: Pressure and Temperature </li></ul><ul><ul><ul><ul><li>As the temperature of an enclosed gas increases, the pressure increases, if the volume is constant. </li></ul></ul></ul></ul><ul><ul><ul><ul><li>LAW- T  , P  </li></ul></ul></ul></ul><ul><ul><li>Constants- moles of gas, Volume </li></ul></ul>P 1 V 1 P 2 V 2 T 1 T 2 = P 1 P 2 T 1 T 2 =
21. 21. <ul><li>Gay-Lussac’s law states that the pressure of a gas is directly proportional to the Kelvin temperature </li></ul><ul><li>if the volume remains constant . </li></ul>
22. 22. 14.3
23. 26. for Sample Problem 14.3
24. 27. <ul><ul><li>The combined gas law allows you to do calculations for situations in which only the amount of gas is constant. </li></ul></ul>
25. 32. for Sample Problem 14.4
26. 33. <ul><ul><li>1. If the volume of a gas in a container were reduced to one fifth the original volume at constant temperature, the pressure of the gas in the new volume would be </li></ul></ul><ul><ul><ul><li>one and one fifth times the original pressure. </li></ul></ul></ul><ul><ul><ul><li>one fifth of the original pressure. </li></ul></ul></ul><ul><ul><ul><li>four fifths of the original pressure. </li></ul></ul></ul><ul><ul><ul><li>five times the original pressure. </li></ul></ul></ul>
27. 34. 14.2 Section Quiz. <ul><ul><li>3. At 46°C and 89 kPa pressure, a gas occupies a volume of 0.600 L. How many liters will it occupy at 0°C and 20.8 kPa? </li></ul></ul><ul><ul><ul><li>0.600 L </li></ul></ul></ul><ul><ul><ul><li>2.58 L </li></ul></ul></ul><ul><ul><ul><li>0.140 L </li></ul></ul></ul><ul><ul><ul><li>2.20 L </li></ul></ul></ul>