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