Thermodynamics

RAT 11

Class Objectives

Be able to define:thermodynamicstemperature, pressure, density,

equilibrium, amount of substancestates of matter and define them in the

context of a phase diagramgas laws

Thermodynamics

Thermodynamics:“Therme” meaning heat, and“Dynamics” meaning strength

Thermodynamics is the science of what is possible and impossible

Major limitation: Cannot predict how long the process takes (This is the subject of rate processes)

Thermodynamic Properties

Temperature = “degree of hotness”

Rapidly moving molecules (atoms) have a high temperature

Slowly moving molecules (atoms) have a low temperatureHigh T Low T

Thermodynamic Properties

Pressure - force per unit area

A

FP

F

A

Impact Weight

Thermodynamic Properties

Density - mass per unit volume

V

M

High densityLow density

Thermodynamic Properties

Amount of Substance – how much is there

………….………………...

1 2 3 12 144 6.022 × 1023

Dozen

Gross

Avogadro’s Number

Pair Exercise 1

A cube of osmium measures 0.2 m on a side. It sits on a table. At the contact between the table and osmium, calculate the pressure (N/m2). Note: Densities may be found in Table

11.1 Foundations of Engineering

States of Matter

Solid Liquid

Gas Plasma

Pressure, Temperature, and State

Plasma

Gas

Vapor

Liquid

Solid

Ttriple Tcritical

Ptriple

Pcritical

Pressure

Temperature

Critical Point

TriplePoint

Gas Laws

apply only to perfect (ideal) gases Boyle’s Law Charles’ Law Gay-Lussac’s Law Mole Proportionality Law

Boyle’s Law

2

12

1 V

V

P

P

T = const n = const

P1

V1

P2

V2

Charles’ Law

1

2

1

2

T

T

V

VT1

V1

T2

V2

P = const n = const

Gay-Lussac’s Law

1

2

1

2

T

T

P

PT1

P1

T2

P2

V = const n = const

Mole Proportionality Law

1

2

1

2

n

n

V

V

T = const P = const

n1

V1

n2

V2

Perfect Gas Law

The physical observations described by the gas laws are summarized by the perfect gas law (a.k.a. ideal gas law)

PV = nRTP = absolute pressureV = volumen = number of molesR = universal gas constantT = absolute temperature

Values for R

Rlbmol·

psia·ft

Rlbmol·

atm·ft

mol·K

atm·L

mol·K

Pa·m

o

3

o

3

3

73.10

7302.0

08205.0

314.8

Rlbmol·

Btu

Rlbmol·

ft·lb

mol·K

cal

mol·K

J

o

of

986.1

1545

987.1

314.8

Pair Exercise 2

A balloon is filled with air to a pressure of 1.1 atm. The filled balloon has a diameter of 0.3 m.

A diver takes the balloon underwater to a depth where the pressure in the balloon is 2.3 atm.

If the temperature of the balloon does not change, what is the new diameter of the balloon?

Energy

Energy is the capacity to do work, but work is a form of energy...

It is easier to think of energy as a scientific and engineering “unit of exchange”, much like money is a unit of exchange.

Example1 car = $20k1 house = $100k5 cars = 1 house

=

Energy Equivalents

A case for nuclear power? 1 kg coal = 42,000,000 joules 1 kg uranium =

82,000,000,000,000 joules (82x1012)

1 kg uranium = 2,000,000 kg coal!!

Heat

Heat is the energy flow resulting from a temperature difference.

NOTE: HEAT AND TEMPERATURE ARE NOT THE SAME!

Example

T = 100oC

T = 0oC

Temperature Profile in Rod

HeatVibrating copper atom

Copper rod

Work

Heat flows due to a temperature “driving force”

Work is the energy flow from any other driving force

Types of Work

Work Driving Force

Mechanical Force (Physical)

Shaft work Torque

Hydraulic Pressure

Electric Voltage

Chemical Concentration

Mechanical Work

F

Fx

Mechanical Work

xF

xxF

xF

dxF

dxFW

xx

x

x

x

x

12

2

1

2

1

2

1

(assume F is not a function of x)

i.e., work is the area under the F vs. x curve

PV Work (Hydraulic)

VP

xAA

F

xFW

x

P PFA

V

P = const

F

Pair Exercise 3

An ideal gas is contained in a closed system. Under constant pressure, the container is compressed from V1 to V2 (volume). Derive the equation for work in terms of the universal gas constant and temperature.