lesson 13 gases and vapors anything in black letters = write it in your notes (‘knowts’)
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Lesson 13Lesson 13
Gases and VaporsGases and Vapors
Anything in black letters = write it in your notes (‘knowts’)
Unit PreviewUnit 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.
ForcePressure =
Area
2
[ ][ ] [ ]
[ ]
NewtonP Pascal
meter
Forces are measured in Newtons and area is measured in meters2
1 kilopascal (kPa) = 1000 Pa
13.1 – The Nature and Properties of Gases13.1 – The Nature and Properties of Gases
Other units of pressuremmHg
p.s.i.
A barometer measures gas pressure
Vacuum
Atmospheric pressure
760 mm Hg (barometric pressure)
253 mm Hg
Sea level On top of Mount Everest
Aneroid Barometer
Aneroid – ‘without fluid’
Atmospheric Pressure (Patm)
The pressure exerted by the gases in atmosphere.
Standard Atmospheric Pressure
1 atm = 101.325 kPa = 760 mmHg = 29.9 inHg = 14.7 p.s.i.
Atmospheric Pressure is Powerful!
101.325 kPa =101,325 N/m2
1 m
1 m
211.4 tonsm
101,325 N
1 m2x
1 lb
4.45 Nx
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?
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
P1V1 = P2V2
V1 V2
T1 V2
=
P1 P2
T1 T2
=
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 kPa
The Combined Gas Law Equation
1 1 2 2
1 2
PV PV
T T
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 Gases14.2 – Ideal Gases
4 variables that describe gases.
Pressure (kPa)
Volume (L)
Temperature (K)
number of particles (mol)
P
V
T
n
PV nRTThe Ideal Gas Law Equation
molKkPaLR 31.8
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 1023 = 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 – Vapors13.3 – 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 101.3 kPa
Boiling point depends on atmospheric pressure
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.
1. Raise/lower flask until Pinside = Poutside (water levels are equal)
PinsidePoutside
Measuring the volume of a gas collected by water displacement.
2. Pgas = Patm – Pwater vapor
Patm Pgas + 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.
8. What does STP stand for (in this class)?
9. If 10 mL of O2 at STP are heated to 100°C, what does the volume become? The pressure remains constant.
10. How many moles of O2 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?