Post on 14-Jan-2016
description
Gas Behavior
formulas from models
§ 18.3–18.4
Ideal Gas Model
• molecules: non-interacting point masses
• collide elastically with surfaces
Temperature T is related to kinetic energy K
• Ktr = 1/2 kT per mode of motion
• k = 1.3806505 10–23 J/K (Boltzmann constant)
RMS Speed
1/2 mv2 = 3/2 kT
v2 = 3kT/m
M = molar mass
3kT/mv = 3RT/M=
Ideal Gas EOS
• What is the pressure?
Lx
Ly
Lz
Ideal Gas Model
• shows expansion with increasing T at constant p
• shows p increase with increasing T at constant V
• shows p = 0 at T = 0 K
Ideal Gas Model
Does not address interaction behavior
• condensation
• mean-free path
• sound transmission
• slow diffusion
van der Waals EOS
• Molecules have volume
• Molecules attract (dimerize)
p =an2
V 2
nRTV – nb
–
Heat Capacity
• Energy to raise the temperature of a sample of gas
Constant-Volume Heating
dU = dK + pdV
Ktr = 3/2 NkT
dKtr = 3/2 NkdT
dV= 0
Cv = dU/dT = 3/2 Nk = 3/2 nR
Heat capacity of an ideal gas
Constant-Volume Heating
dU = dK + pdV
Ktr = 3/2 NkT; Krot = 2/2 NkT
dKt = 5/2 NkdT
dV= 0
Cv = dU/dT = 5/2 Nk = 5/2 nR
Heat capacity of a diatomic gas
Heat Capacities of Solids
Six modes of motion
Kvib in x, y, z directions
Uel in x, y, z directions
U = 6N(1/2 kT) = 3NkT
dU = 3NkdT
dV 0
Cv = dU/dT = 3 Nk = 3 nR
Law of Dulong and Petit
Phases of Matter
Behavior and diagrams
§ 18.6
Variables and Diagrams
• State Variables: p, V, n, T
• Hard to visualize in 2-D
• Useful plots: p-V, p-T
p-V plots
Ideal gas
Source: Y&F, Figure 18.6
Real Substance
Source: Y&F, Figure 18.7
p-T plot
Gas
Source: Y&F, Figure 17.5b
p-T plotPhase Diagram
Source: Y&F, Figure 18.24
p-V-T SurfaceIdeal Gas
Source: Y&F, Figure 18.27
p-V-T SurfaceReal Substance
Source: Y&F, Figure 18.26