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!

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 (kPa) = 1000 Pa 13.1 – The Nature and Properties of Gases

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

Aneroid Barometer Aneroid – ‘without fluid’

Atmospheric Pressure (P atm ) The pressure exerted by the gases in atmosphere. Standard Atmospheric Pressure 1 atm = kPa = 760 mmHg = 29.9 inHg = 14.7 p.s.i.

Atmospheric Pressure is Powerful! kPa =101,325 N/m 2 1 m 101,325 N 1 m 2 x 1 lb 4.45 N x 1 ton 2000 lb

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? the volume (V) of the container increases? the number of molecules (n) increases? P ↑ P ↓ P ↑ Boyle’s Law

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

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

T k = T c + 273

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

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

14.2 – Ideal Gases 4 variables that describe gases. Pressure (kPa) Volume (L) Temperature (K) number of particles (mol) PVTnPVTn

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 Lorenzo Romano Amedeo Carlo Avogadro di Quaregna e di Cerreto (1776 – 1856) Also came up with the idea of the mole 6.02 x = Avogadro’s Number Equal volumes of gases, at the same temp and pressure, contain the same number of molecules.

1 mole of any gas has a volume of 22.4 L at STP. The molar volume of a gas at STP. Use the ideal gas law to calculate the volume of 1 mole of any 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 kPa?

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 - 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

Normal Boiling Point - temp where v.p. of liquid equals kPa Boiling point depends on atmospheric pressure Higher elevations have lower P atm, 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.

1. Raise/lower flask until P inside = P outside (water levels are equal) P inside P outside

Measuring the volume of a gas collected by water displacement. 2. P gas = P atm – P water vapor P atm P gas + P water 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.

8. What does STP stand for (in this class)? 9. If 10 mL 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=nRT stand for? What units should be used in PV=nRT? 500mL of any gas would contain how many moles at STP? Lesson 13 Review

What is the normal boiling point of ethanol? What is the boiling point of water when atmospheric pressure is 60kPa?