1 / 28

Gases

Gases. Chapter 14. Review from Chapter 13. Pressure Describing gases : To describe a gas fully, you need to state the 4 measurable quantities: 1. Volume 3. Temperature 2. # of molecules 4. Pressure Definition: The force per unit of area on a surface Equation:.

zoltin
Télécharger la présentation

Gases

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Gases Chapter 14

  2. Review from Chapter 13 Pressure • Describing gases: To describe a gas fully, you need to state the 4 measurable quantities: 1. Volume 3. Temperature 2. # of molecules 4. Pressure • Definition: The force per unit of area on a surface • Equation:

  3. Measuring Pressure • A barometeris a device used to measure atmospheric pressure • Introduced by Torricelli with experiments involving mercury (Hg) • He determined the air (atmosphere) could support a column of Hg 760 mm high • The height of the Hg depends on the air pressure • What would happen to the height of the column in the mountains? • What would happen to the height of the column 100ft under water?

  4. Units of Pressure • Pressure can be measured in many units • Most common: mm of Hg • 1 mm Hg = 1 torr (in honor of Torricelli) • Atmospheric Pressure at sea level and 0oC is 760 mm Hg • Other units of pressure include: Atmospheres (atm) and Pascal (Pa)

  5. CONVERSIONS 760 mm Hg= = 760 torr = 1 atm = 29.92 in Hg = 14.7 psi = 101325 Pa = 101.325 kPa

  6. Standard Temperature and Pressure (STP) • To compare volume of gases, it is necessary to know the pressure at which the volume is measured • For purpose of comparison, scientists have agreed on standard conditions • STP= 1 atm pressure and 0oC

  7. Review Calculation • The atmospheric pressure in Denver is 0.830 atm. Express this in mmHg and kPa.

  8. Boyle’s Law • Robert Boyle studied the relationship between pressure and volume • Boyle’s Law: States that the volume of a fixed mass of gas varies inverselywith the pressure at constant temperature • Can be written as:P1V1= P2V2

  9. Practice Problem P1V1= P2V2 • A sample of oxygen gas has a volume of 150. mL when its pressure is 0.947 atm. What will the volume of the gas be at a pressure of 0.987 atm if the temperature remains constant? • P1= • V1= • P2= • V2=

  10. Charles’s Law • Jacques Charles studied the relationship between volume and temperature • Charle’s Law: States that the volume of a fixed mass of gas at constant pressure varies directly with the Kelvin temperature. • Can be written as:

  11. Kelvin Temperature? • The Kelvin scale is K= 273 + oC • -273 oC is the lowest possible temperature to achieve (absolute zero) • Absolute zero is given the value of zero on the Kelvin scale

  12. Practice Problem A sample of neon gas occupies a volume of 752 mL at 25 oC. What will the volume of the gas occupy at 50oC if the pressure remains constant? • V1= • T1= • V2= • T2=

  13. Gay-Lussac’s Law • Gay-Lussac determined the relationship between temperature and pressure • Gay-Lussac’s Law: The pressure of a fixed mass of gas at constant volume varies directly with the Kelvin temperature • Can be written as: Pressure (atm)

  14. Practice Problem • The gas in an aerosol can is at a pressure of 3.00 atm at 25oC. Directions on the can warn the user not to keep in a place where the temperature exceeds 52oC. What would the pressure in the can be at the 52oC? • P1= • T1= • P2= • T2=

  15. The Combined Gas Law • A gas sample often undergoes changes in temperature, pressure and volume. • Combining all three (Boyle’s, Charles’, and Gay-Lussac’s) will give us a valid equation • Can be written as:

  16. Practice Problem • A helium filled balloon has a volume of 50.0 L at 25oC and 1.08 atm. What volume will it have at 0.855 atm and 10.oC? • P1= • T1= • V1 = • P2= • T2= • V2 =

  17. Avogadro’s Principal • Equal volumes of gases at the same temperature and pressure contain equal numbers of particles • From Chapter 11: 1 mole= 6.02 x1023 particles • Molar volume for a gas is the volume that one mole occupies at 0.00oC and 1.00 atm pressure. (STP conditions) • Avogadro showed experimentally that one mole of any gas will occupy a volume of 22.4L at STP. • Conversion Factor:

  18. Practice Problem • What volume will 0.416 g of krypton gas occupy at STP?

  19. The Ideal Gas Law • Describes the physical behavior of an ideal gas in terms of pressure, volume, temperature, and the number of moles of gas present PV=nRT • R represents an experimentally determined constant that is referred to as the ideal gas constant (depends on the units used for pressure)

  20. Real vs. Ideal Gas • An ideal gas is one whose particles take up no space and have no intermolecular attractive forces • In the real world, no gas is truly ideal. • Real gases deviate most from ideal gas behavior at extremely high pressures and low temperatures

  21. Practice Problem • What is the pressure in atm exerted by a 0.500 mol samples of nitrogen gas in a 10.0L container at 298K?

  22. Applying the Ideal Gas Law • Rearranging the PV=nRT equation allows you to also calculate the molar mass and density of a gas sample if the mass of the sample is known • Recall from Chapter 12- n (moles) = m (mass)/ M (molar mass) • D= Density (mass/volume)

  23. Practice Problem • Calculate the grams of N2 gas present in a 0.600 L sample kept at 1.00 atm pressure and a temperature of 22.0oC.

  24. Gas Stoichiometry Why are we using stoichiometry? • Suppose we need to determine the volume of something other than our known (the given), we can apply stoichiometry to achieve the desired products/reactants • “Plan of Attack” • Start with a BALANCED equation. • Use stoichiometry first to get into the desired substance • Use the Ideal Gas Law (IGL) to convert into volume of that substance Gas volume A moles A moles B mass B Mass A moles A moles B gas volume B

  25. Practice Problem • What volume of chlorine gas at 38oC and 1.63 atm is needed to react completely with 10.4 g of sodium to form NaCl? (Cl2 + 2Na  2NaCl)

More Related