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Chapter 5

Chapter 5. Gases. General Gas Properties. What are the general properties of all gases?. Take on the shape and volume of the container Can be compressed Mix well together Low densities. Prior Knowledge. Please define the following words as completely as possible: Pressure Volume

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Chapter 5

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  1. Chapter 5 Gases

  2. General Gas Properties • What are the general properties of all gases? Take on the shape and volume of the container Can be compressed Mix well together Low densities

  3. Prior Knowledge • Please define the following words as completely as possible: • Pressure • Volume • Temperature

  4. Pressure of a Gas Why do gases exert internal pressure? Gas molecules will push against any surface they come into contact with because they are always moving

  5. Pressure of a Gas How is pressure defined? • Units: • Pascals (Pa) • Atmospheres (atm) • mm of Hg (mmHg) • Torr (torr)

  6. Pressure of a Gas What is the difference between pressure and atmospheric pressure? Atm. pressure is the external pressure exerted by the atmosphere due to gravity Changes based on location, elevation temperature and weather

  7. Pressure of a Gas • What device measures atmospheric pressure? • Barometer • (atmosphere) • Manometer • (non-atmosphere)

  8. Volume of a Gas What is the volume of a gas? • A measure of the amount of space that gas particles occupy • Units: • Liters (L) or cubic decimeters (dm3) • Milliliters (mL) or cubic centimeters (cm3)

  9. Temperature of a Gas What is the temperature of a gas? • A measure of the amount of energy that the gas particles possess • Directly related to kinetic energy (and thus the velocity) of the gas particles • Units: • Degrees Fahrenheit (°F) • Degrees Celsius (°C) • Kelvin (K)

  10. Relationships What is the difference between direct and indirect relationships? Indirect – as the ind. variable increases, the dep. variable decreases and vice versa Direct – as the ind. variable increases, the dep. variable increases and vice versa Constant means the value doesn’t change

  11. P-V Hypothesis With temperature (T) constant, what do you think the relationship between the change in pressure (P) and volume (V) will be? Why?

  12. V-T Hypothesis With P constant, what do you think the relationship between the change in T and V will be? Why?

  13. P-T Hypothesis With V constant, what do you think the relationship between the change in T and P will be? Why?

  14. Regroup and Discuss Observations from the simulation: P-V relationship, T constant V-T relationship, P constant P-T relationship, V constant

  15. Moles With T and P constant, what was the relationship between the change in the moles (n) and the V?

  16. Combining Everything • V α 1/P (Boyle) • V α T (Charles) • P α T (Amonton) • V α n (Avogadro) • We combine them to form an all-in-one proportion: • V αnT/P • What are all of the gas law proportions?

  17. The Ideal Gas Law The Ideal Gas Law Can also be rearranged for initial and final conditions: What equation is generated from our all-in-one proportion?

  18. Gas Constant • Symbol - R • R = 8.31 J/(K*mol) • Table 2 in Data Booklet • R = 0.0821 atm* L/(K*mol) • Not in your booklet • It is a proportionality constant that allows us to turn a proportion into an equation What is the significance of the gas constant?

  19. STP • STP = Standard Temperature and Pressure • T = 273 K • P = 1 atm • 22.4 L What does STP stand for? What volume does 1 mole of an ideal gas occupy at STP?

  20. Conversions

  21. Pressure Conversions How do you convert between the different pressure units? • 1 atm = 760 mmHg • 1 atm = 760 torr • 1 atm = 1.01 x 105 Pa • Table 2 in Data Booklet

  22. Ideal Gas Law Practice • 5.30 – Given that 6.9 moles of carbon monoxide gas are present in a container of volume 30.4 L, what is the pressure of the gas (in atm) if the temperature is 62°C? • 6.2 atm • 5.38 – The volume of a gas at STP is 488 mL. Calculate its volume, in liters, at 22.5 atm and 150°C. • 0.0336 L

  23. More Ideal Gas Law Practice 1.9 atm 0.82 L 0.0059 atm

  24. Ideal Gas Law Tricks • Using the ideal gas law, how do you solve for: • Mass • Molar Mass • Density • You need to break moles down and rearrange your formula • n = m/MM = PV/RT • m = (MM)PV/RT • MM = mRT/PV • d = m/V = P(MM)/RT

  25. Ideal Gas Laws Tricks Practice • 5.46 – Calculate the density of hydrogen bromide gas, in g/L, at 733 mmHg and 46°C. • 3.0 g/L • 5.48 – A compound has the empirical formula SF4. At 20°C, 0.100 g of the gaseous compound occupies a volume of 22.1 mL and exerts a pressure of 1.02 atm. What is the molecular formula of the gas? • SF4

  26. Gas Stoichiometry Walkthrough • Practice 5.12 - Assuming no change in temperature or pressure, calculate the volume of oxygen, in liters, required for the complete combustion of 14.9 L of butane (C4H10). • Balance your equation • 2C4H10(g) + 13O2(g) → 8CO2(g) + 10H2O(g) • Determine your molar ratio • 2:13 • Use the molar ratio to determine the new volume • 14.9/x = 2/13 • x = 96.9 L

  27. Gas Stoichiometry Practice • Note: Sometimes you need to solve for moles, mass or volume first! • 5.54 – Ethanol burns in air. Determine the volume of the air in liters at 35˚C and 790 mmHg to burn 227 g of ethanol. Assume that air is 21.0% oxygen by volume. C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l) • 1.71 x 103 L of air

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