Lesson 13 Gases and Vapors Anything in black

Lesson 13 Gases and Vapors Anything in black letters = write it in your notes (‘knowts’)

Unit Preview Atoms and molecules are always moving, even in a solid or liquid. Gas molecules are very far apart from one another and can be compressed easily. This unit is about gases and vapors. Remember that air is a gas also!

13. 1 – The Nature and Properties of Gases Gas particles are constantly moving and exert a force on the container. Forces are measured in Newtons and area is measured in meters 2 1 kilopascal (k. Pa) = 1000 Pa

Other units of pressure Vacuum mm. Hg p. s. i. Atmospheric pressure 760 mm Hg (barometric pressure) 253 mm Hg Sea level On top of Mount Everest A barometer measures gas pressure

Aneroid Barometer Aneroid – ‘without fluid’

Atmospheric Pressure (Patm) The pressure exerted by the gases in atmosphere. Standard Atmospheric Pressure 1 atm = 101. 325 k. Pa = 760 mm. Hg = 29. 9 in. Hg = 14. 7 p. s. i.

Atmospheric Pressure is Powerful! 1 m 1 m 101. 325 k. Pa =101, 325 N/m 2 101, 325 N 1 m 2 x 1 lb 4. 45 N x 1 ton 2000 lb

Atmospheric Pressure is Powerful!

Atmospheric Pressure is Powerful! Empty space with no particles or pressure is called a vacuum.

Solids and liquids are NOT easily compressible; gases are. Why do you think gases are compressible? - there is a large amount of space between gas particles.

What will happen to the pressure (P) of a gas if… the temperature (T) increases? P↑ the volume (V) of the container increases? P ↓ Boyle’s Law the number of molecules (n) increases? P↑

What will happen to the volume (V) of a gas if… the temperature (T) increases? V↑ Charles’s Law the pressure (P) on the gas increases? V ↓ Boyle’s Law the number of molecules (n) increases? V↑

Three Gas Law Equations… Boyle’s Law P 1 V 1 = P 2 V 2 Charles’s Law V 1 T 1 Gay-Lussac’s Law = P 1 T 1 V 2 = P 2 T 2

Tk = Tc + 273

The volume of a gas depends on its temperature and pressure. STP – Standard Temperature & Pressure Standard Temp = 0°C = 273 K Standard Pressure = 101. 3 k. Pa

The Combined Gas Law Equation Why is it called “The Combined Gas Law”? - it combines Charles’s, Boyle’s and Gay-Lussac’s Laws into one T MUST be in kelvin

14. 2 – Ideal Gases 4 variables that describe gases. P Pressure (k. Pa) V Volume (L) T Temperature (K) n number of particles (mol)

The Ideal Gas Law Equation universal gas constant

Ideal gases do not exist, but real gases behave like ideal gases at many conditions of temperature and pressures. The particles of an ideal gas have no volume, and there is no attraction between them.

Avogadro’s Hypothesis Equal volumes of gases, at the same temp and pressure, contain the same number of molecules. Lorenzo Romano Amedeo Carlo Avogadro di Quaregna e di Cerreto (1776 – 1856) Also came up with the idea of the mole 6. 02 x 1023 = Avogadro’s Number

Use the ideal gas law to calculate the volume of 1 mole of any gas at STP. 1 mole of any gas has a volume of 22. 4 L at STP. The molar volume of a gas at STP.

1. What is the volume of 1 mole of nitrogen gas at STP? 2. What is the volume of 1 mole of nitrogen gas at 22°C and 99. 8 k. Pa?

13. 3 – Vapors Temperature is a measure of the AVERAGE kinetic energy of molecules. Molecules with higher than average kinetic energy can evaporate. Kinetic Energy (KE) – energy due to motion.

Vapor pressure due to evaporating particles of a solid or liquid. A substance with a high vapor pressure (volatile) will evaporate quickly. Vapor pressure increases as temp increases. When the vapor pressure of a liquid equals atmospheric pressure, boiling occurs.

Vapor Pressure of Water

Boiling point depends on atmospheric pressure Normal Boiling Point temp where v. p. of liquid equals 101. 3 k. Pa Higher elevations have lower Patm, so water boils at a lower temperature (not as hot).

Molecules with higher KE evaporate The molecules left behind have a lower average KE Evaporation is a COOLING PROCESS!! “Evaporation is COOL!”

Evaporation occurs at the surface of a liquid, boiling occurs throughout the liquid.

Dynamic Equilibrium – vaporization rate = condensation rate.

Measuring the volume of a gas collected by water displacement.

Measuring the volume of a gas collected by water displacement. Poutside Pinside 1. Raise/lower flask until Pinside = Poutside (water levels are equal)

Measuring the volume of a gas collected by water displacement. Patm Pgas + Pwater vapor 2. Pgas = Patm – Pwater vapor

Lesson 13 Review 1. Define Pressure. 2. State 3 units of pressure 3. What is a volatile liquid? 4. Explain how evaporation is a cooling process. 5. What is vapor pressure? 6. When does boiling occur? 7. Explain the difference between boiling & evaporation.

Lesson 13 Review 8. What does STP stand for (in this class)? 9. If 10 m. L of O 2 at STP are heated to 100°C, what does the volume become? The pressure remains constant. 10. How many moles of O 2 are in problem 9?

Lesson 13 Review State Avogadro’s Hypothesis What is the volume of 1 mol of any gas at STP? What does each letter in PV=n. RT stand for? What units should be used in PV=n. RT? 500 m. L of any gas would contain how many moles at STP?

What is the normal boiling point of ethanol? What is the boiling point of water when atmospheric pressure is 60 k. Pa?