Chem 6B Equation Sheet (Exam 1)
1
Prof. Crowell
Chem 6B Exam 1 Equation Sheet
1
st
Law
:
the total amount of energy in the universe is constant (energy is conserved).
U
q
w
∆
=
+
2
nd
Law
:
in any spontaneous change the entropy of the universe increases.
0
universe
S
∆
>
∆
>
∆
>
∆
>
3
rd
Law
: the entropy of any pure, perfect crystalline solid at absolute zero is zero.
system
S
0
0
at
K
=
!
State Function
:

a physical property like U, H, T, V, P that has a specific value once the state is
defined; it depends only on the state of the system and not the pathway.
Extensive Variables
:

properties that depend upon the amount (mass) or “extent” of the
sample (e.g. M, n, V, C, U, S, G, etc.).
Intensive Variables
:

properties that depend upon the
nature but not on the amount (e.g. T, P,
η
,
ρ
= M/V,
χ
i
= n
i
/n, V/n,
U/n, S/n, H/n, G/n, etc.).
An open system can exchange both matter & energy
with its surroundings.
A closed system can exchange
energy
with the surroundings but not matter.
An isolated system cannot exchange energy nor matter.
Diathermic Walls
allow energy to flow as heat if there is a temperature difference between the system &
surroundings, whereas Adiabatic Walls
do not allow heat to flow even if there is a T difference.
Reversible Process
° A process involving a series of
infinitesimal changes
.
At each step in a reversible
process, the system is in mechanical equilibrium with its surroundings.
Irreversible Process
° A process in which change occurs by
finite
amounts.
With finite steps, the system is
not in mechanical equilibrium (e.g. P or T) with its surroundings during each step in the process.
The work done in the expansion process approaches the reversible process as the number of steps becomes larger.
The maximum work that can be done in an expansion is during a reversible process.
Work
is the energy transferred between a system and its surroundings as a result of
unbalanced forces between the two, such as when an object is moved by a force.
work = force x distance = Nm = kgm
2
/s
2
= J,
Expansion work =  P
ex
∆
V
= Pam
3
= J
U
= internal energy = KE + PE = system capacity to do work = total energy storage of a system
Sign convention is viewed from the perspective of the
system
:
Heat and work are both positive
when they
enter
the system, and are both negative when they
leave
the system.
Ideal gas law:
First law of thermodynamics:
Expansion work against a constant external pressure:
Work of reversible, isothermal expansion of an ideal gas:
ln
ext
final
init
PV
nRT
U
q
w
w
P
V
V
w
nRT
V
=
∆
=
+
=
= −
∆
= −
Isothermal
⇒
Constant
Temperature
with corresponding changes in Pressure
, Volume
, and with Heat
added
or removed.
;
ln
;
0
0
final
init
V
PV
const
w
nRT
T
U
q
w
V
=
= −
∆
=
=
= −
∆
⇒
∆
=
⇒
= −
= −
Isobaric
⇒
Constant
Pressure
with corresponding changes in Volume
, Temperature
, and with Heat
added or
removed.
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 Winter '08
 Crowell
 Thermodynamics, Energy, Entropy, Chem 6B Equation, 6B Equation Sheet

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