# Chapter 9 – Thermodynamics - CourseSaver.com

Μηχανική

27 Οκτ 2013 (πριν από 4 χρόνια και 8 μήνες)

87 εμφανίσεις

Gen Chem Day 6
-
Thermodynamics

Three laws of thermodynamics

1) Conservation of energy (Energy can’t be created or destroyed).

2) For a spontaneous process, the entropy of the universe increases.

3) A perfect crystal at 0K has zero entropy.

E = q + w

w

=
-
P

V

Gas in a piston

1)

Transfer of heat (lock piston)

2)

Expanding gases cool; compressing gases warm

3)

Isobaric

(

P = 0)

4)

Isochoric

(

V = 0

so w = 0
)

5)

Isothermal

(

T = 0

so

E = 0
)

6)

(q = 0)

State Functions

Entropy (S)

Phases of matter

S for rxns

S =

n
S
products

-

n
S
reactants

Enthalpy (H)

Exothermic

(

H<0)
/

Endothermic

(

H>0)

Bond Enthalpies

H =

D
broken

-

D
formed

Bond breaking is endothermic

Bond making is exothermic

Whatis

H for the following rxn?

Enthalpies of Formatio
n

H =

n

H
f,products

-

n

H
f,reactants

Given the following
standard enthalpy of formation

values, calculate the

H

rxn

of the following reaction:

PCl
3
(g) + 3HCl(g)

3Cl
2
(g) + PH
3
(g)

Compound

PCl
3
(g)

HCl(g)

PH
3
(g)

H
f

(kJ/mol)

288.07

92.30

5.40

Bond Enthalpies (kJ/mol)

C
-
H

413

C
-
Cl

328

Cl
-
Cl

242

H
-
Cl

431

Hess’s Law

C
2
H
4
(g) + 6F
2
(g)

2CF
4
(g) + 4HF(g)

H = ?

H
2
(g) + F
2
(g)

2HF(g)

H =
-
537kJ

C(s) + 2F
2
(g)

CF
4
(g)

H =
-
680kJ

2C(s) + 2H
2(g)

C
2
H
4(g)

H = +52.3kJ

Gibb’s Free Energy (G)

G =

n

G
f,products

-

n

G
f,react
ants

G =

G

+ RTlnQ

G

=
-
RTlnK
eq

G =

H
-

T

S

G㰰

S灯ptane潵s

G㸰

N潮s灯ptane潵s

G㴰

At e煵ilibri畭

H

S

-

+

Spontaneous at all temperatures

+

-

Non
-
spontaneous at all temperatures

-

-

Spontaneous at low temperatures

+

+

Spontaneous at high temperatures