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DEVIL PHYSICS THE BADDEST CLASS ON CAMPUS IB PHYSICS-2
DEVIL PHYSICSTHE BADDEST CLASS ON
CAMPUSIB PHYSICS-2
TSOKOS LESSON 3-3IDEAL GASES
IB Assessment Statements
Topic 10.2., Thermal Physics: Processes10.2.1. Deduce an expression for the
work involved in a volume change of a gas at constant pressure.
10.2.2. State the first law of thermodynamics.
10.2.3. Identify the first law of thermodynamics as a statement of the principle of energy conservation.
IB Assessment Statements
Topic 10.2., Thermal Physics: Processes10.2.4. Describe the isochoric
(isovolumetric), isobaric, isothermal and adiabatic changes of state of an ideal gas.
10.2.5. Draw and annotate thermodynamic processes and cycles on P-V diagrams.
IB Assessment Statements
Topic 10.2., Thermal Physics: Processes10.2.6. Calculate from a P-V
diagram the work done in a thermodynamic cycle.
10.2.7. Solve problems involving state changes of a gas.
Objectives
State the definition of pressure, P = F/A
Understand that an ideal gas is a gas in which the molecules do not exert forces on each other except when colliding
Understand that an ideal gas obeys the law, PV = nRT at all pressures, temperatures and volumes
Objectives
Understand the ideal gas law and solve problems using it
Appreciate that pressure in a gas develops as a result of collisions between the molecules and the walls of the container in which the momentum of the molecules changes
22
22
11
11
Tn
VP
Tn
VP
Video – Developing the Gas Laws
Pressure
Force per unit area Only the force normal to the area Unit is the Pascal (Pa) or Nm-2
Atmospheric pressure is 1.013 x 105 Pa
A
FP
cos
Moles of Gases
Convenient to use moles (not the furry kind)
Avogadro's Avocado number
Atomic Mass = Molar Mass = grams/mol
mol
moleculesxN A
231002.6
Moles of Gases
The number of moles can be found by dividing the number of molecules, N, by the Avogadro's Avocado number
Also found by dividing the mass of the gas in grams by the Atomic / Molar Mass
AN
Nn
)/(
)(
molg
gmn
Boyle-Mariotte Law At constant temperature
and with a constant quantity of gas, pressure is inversely proportional to volume
The graph of pressure versus volume is a hyperbola, aka an isothermal curve
2211
tan
VPVP
tconsPV
Volume-Temperature Law
When the temperature is expressed in Kelvin and pressure is kept constant, volume and temperature are proportional to each other
2
2
1
1
tan
T
V
T
V
tconsT
V
Volume-Temperature Law When the temperature is expressed in
Kelvin and pressure is kept constant, volume and temperature are proportional to each other
2
2
1
1
tan
T
V
T
V
tconsT
V
Graph of different quantities of the same gas or same gas at different pressures
Pressure-Temperature Law
When the temperature is expressed in Kelvin and volume is kept constant, pressure and temperature are proportional to each other
2
2
1
1
tan
T
P
T
P
tconsT
P
Pressure-Temperature Law
When the temperature is expressed in Kelvin and volume is kept constant, pressure and temperature are proportional to each other
2
2
1
1
tan
T
P
T
P
tconsT
P
Equation of State
nRTPV
molJKR
tconsnT
PV
tconsT
PV
1131.8
tan
tan
Ideal Gas Law
An ideal gas will obey this law at all temperatures, pressures and volumes.
Real gases obey this law only for a certain range of temperatures, pressures and volumes.
22
22
11
11
Tn
VP
Tn
VP
nRTPV
Σary Review
Can you state the definition of pressure, P = F/A?
Do you understand that an ideal gas is a gas in which the molecules do not exert forces on each other except when colliding?
Do you understand that an ideal gas obeys the law, PV = nRT at all pressures, temperatures and volumes?
Σary Review
Do you understand the ideal gas law and can you solve problems using it?
Do you appreciate that pressure in a gas develops as a result of collisions between the molecules and the walls of the container in which the momentum of the molecules changes?
22
22
11
11
Tn
VP
Tn
VP
IB Assessment Statements
Topic 10.2., Thermal Physics: Processes10.2.1. Deduce an expression for the
work involved in a volume change of a gas at constant pressure.
10.2.2. State the first law of thermodynamics.
10.2.3. Identify the first law of thermodynamics as a statement of the principle of energy conservation.
IB Assessment Statements
Topic 10.2., Thermal Physics: Processes10.2.4. Describe the isochoric
(isovolumetric), isobaric, isothermal and adiabatic changes of state of an ideal gas.
10.2.5. Draw and annotate thermodynamic processes and cycles on P-V diagrams.
IB Assessment Statements
Topic 10.2., Thermal Physics: Processes10.2.6. Calculate from a P-V
diagram the work done in a thermodynamic cycle.
10.2.7. Solve problems involving state changes of a gas.
QUESTIONS
#1-19
Homework
