Chapter 9 – Thermodynamics - CourseSaver.com

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27 Οκτ 2013 (πριν από 3 χρόνια και 7 μήνες)

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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)

Adiabatic

(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