Thermodynamics
Mar 19, 2016
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
AFP
F
A
Impact Weight
Thermodynamic Properties Density - mass per unit volume
VM
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 VV
PP
T = const n = const
P1
V1
P2
V2
Charles’ Law
1
2
1
2
TT
VV
T1
V1
T2
V2
P = const n = const
Gay-Lussac’s Law
1
2
1
2
TT
PP
T1
P1
T2
P2
V = const n = const
Mole Proportionality Law
1
2
1
2
nn
VV
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 = nRT
P = absolute pressureV = volumen = number of molesR = universal gas constantT = absolute temperature
Values for R
Rlbmol·psia·ft
Rlbmol·
atm·ft
mol·Katm·L
mol·KPa·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!
ExampleT = 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 ForceMechanical Force (Physical)
Shaft work Torque
Hydraulic Pressure
Electric Voltage
Chemical Concentration
Mechanical Work
F
Fx
Mechanical Work
xFxxF
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
xAAF
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.