1. The document discusses key concepts in chemical thermodynamics including energy, heat, work, temperature, and the first law of thermodynamics. 2. It defines important terms and units used to describe thermodynamic processes and explains that energy cannot be created or destroyed, only converted from one form to another. 3. The document also covers spontaneous processes and reversible processes, stating that spontaneous processes occur without outside intervention and reversible processes can return a system and its surroundings to their original states through an exact reversal.

1. Chemical Thermodynamics
‫الحرارية‬ ‫الديناميكا‬ ‫كيمياء‬
1Dr. Wael A. El-Helece

2. Chemical
Thermodynamics
Contents ‫المحتويات‬
1.Some Terminology ‫بعض‬‫المفاهيم‬
2.Heat ‫الحرارة‬
3.Heats of Reaction and Calorimetry ‫الحراري‬ ‫والمسعر‬ ‫التفاعل ت‬ ‫حرارة‬
4.Work ‫الشغل‬
5.The First Law of Thermodynamics ‫للديناميكا‬ ‫الول‬ ‫القانون‬
‫الحرارية‬
6.Heats of Reaction: ∆U and ∆H ‫التفاعل‬ ‫حرارا ت‬
2Dr. Wael A. El-Helece

3. Chemical
Thermodynamics
Contents ‫المحتويات‬
7.The Indirect Determination of ∆H, Hess’s Law
‫هس‬ ‫وقانون‬ ‫الحرارى‬ ‫المحتوى‬ ‫فى‬ ‫للتغير‬ ‫المباشر‬ ‫غير‬ ‫التعين‬
8.Standard Enthalpies of Formation
‫القياسية‬ ‫التكون‬ ‫حرارا ت‬
9.Fuels as Sources of Energy
‫للطاقة‬ ‫كمصدر‬ ‫الوقود‬ ‫خليا‬
10.Focus on Fats, Carbohydrates, and Energy Storage
‫الطاقة‬ ‫وتخزين‬ ‫والكربوهيدرا ت‬ ‫الدهون‬ ‫على‬ ‫نظرة‬
3Dr. Wael A. El-Helece

4. Chemical
Thermodynamics
Some Terminology
‫المصطلحات‬ ‫بعض‬
• System
•‫النظام‬
• Surroundings
•‫المحيط‬
4Dr. Wael A. El-Helece

5. Chemical
Thermodynamics
Terminology
‫المصطلحا ت‬
• Energy, U ‫الطاقة‬
The capacity to do work. ‫شغل‬ ‫بذل‬ ‫على‬ ‫القدرة‬
• Work ‫الشغل‬
Force acting through a distance.‫على‬ ‫المؤثرة‬ ‫القوة‬
‫المساحة‬
• Kinetic Energy ‫الحركة‬ ‫طاقة‬
The energy of motion. ‫الحركة‬ ‫على‬ ‫القدرة‬5Dr. Wael A. El-Helece

6. Chemical
Thermodynamics
Energy
‫الطاقة‬
• Kinetic Energy ‫الحركة‬ ‫طاقة‬
ek =
1
2
mv2
[ek ] =
kg m2
s2 = J
w = Fd [w ] =
kg m
s2 = Jm
• Work ‫الشغل‬
‫القانو‬
‫ن‬
‫القانو‬
‫ن‬
‫وحدة‬
‫القياس‬
‫وحدة‬
‫القياس‬
6Dr. Wael A. El-Helece

7. Chemical
Thermodynamics
Energy
‫الطاقة‬
• Potential Energy ‫الوضع‬ ‫طاقة‬
Energy due to condition, position, or
composition. ‫او‬ ‫الموضع‬ ‫او‬ ‫الظرف‬ ‫نتيجة‬ ‫الطاقة‬
‫التركيب‬
Associated with forces of attraction or repulsion
between objects. ‫بين‬ ‫والتنافر‬ ‫الجذب‬ ‫بقى‬ ‫مصحوبة‬ ‫تكون‬
‫الجزيئات‬
• Energy can change from potential to 7Dr. Wael A. El-Helece

8. Chemical
Thermodynamics
Energy and Temperature
‫الحرارة‬ ‫ودرجة‬ ‫الطاقة‬
• Thermal Energy ‫الحرارية‬ ‫الطاقة‬
Kinetic energy associated with random molecular motion.
‫عشوائيا‬ ‫الجزيئات‬ ‫بحركة‬ ‫مصحوبة‬ ‫حركة‬ ‫طاقة‬
proportional to temperature.
‫الحرارة‬ ‫درجة‬ ‫مع‬ ‫طرديا‬ ‫تتناسب‬
An intensive property. )‫مركزة‬ ‫داخلية‬ ‫)خاصية‬
• Heat and Work ‫والشغل‬ ‫الحرارة‬
q and w.
Energy changes. ‫الطاقة‬ ‫تغيرات‬
8Dr. Wael A. El-Helece

9. Chemical
Thermodynamics
Heat ‫الحرارة‬
Energy transferred between a system and its surroundings
as a result of a temperature difference.
.‫الحرارة‬ ‫درجا ت‬ ‫فى‬ ‫لفرق‬ ‫كنتيجة‬ ‫محيطه‬ ‫إلى‬ ‫النظام‬ ‫من‬ ‫الطاقة‬ ‫تنتقل‬
• Heat flows from hotter to colder.
.‫البرد‬ ‫إلى‬ ‫السخن‬ ‫من‬ ‫الحرارة‬ ‫تنتقل‬
Temperature may change.
.‫الحرارة‬ ‫درجة‬ ‫تغير‬ ‫المكان‬ ‫فى‬
Phase may change (an isothermal process).
.(‫حراريا‬ ‫)متعادلة‬ ‫تتغير‬ ‫أن‬ ‫ممكن‬ ‫الحالة‬
9Dr. Wael A. El-Helece

10. Chemical
Thermodynamics
Units of Heat
‫الحرارة‬ ‫قياس‬ ‫وحدات‬
• Calorie (cal) ‫الكالورى‬
The quantity of heat required to change the temperature of one
gram of water by one degree Celsius.
‫الماء‬ ‫من‬ ‫جرام‬ ‫واحد‬ ‫حرارة‬ ‫درجة‬ ‫لرفع‬ ‫اللزمة‬ ‫الحرارة‬ ‫كمية‬
.‫مئوية‬ ‫واحدة‬ ‫درجة‬
• Joule (J) ‫الجول‬
SI unit for heat ‫الدولي‬ ‫النظام‬ ‫فى‬ ‫الحرارة‬ ‫قياس‬ ‫وحدة‬
‫للوحدات‬
1 cal = 4.184 J
10Dr. Wael A. El-Helece

11. Chemical
Thermodynamics
Chemical Thermodynamics
‫الحرارية‬ ‫الديناميكا‬ ‫كيمياء‬
 Science of interconversion of energy
.‫والطاقة‬ ‫المادة‬ ‫وتداخل‬ ‫الطاقة‬ ‫تحول‬ ‫يتناول‬ ‫الذى‬ ‫العلم‬
 Heat into other forms of energy
.‫الطاقة‬ ‫من‬ ‫أخرى‬ ‫أشكال‬ ‫إلى‬ ‫الحرارة‬
 Amount of heat gained/released from a system
.‫النظام‬ ‫بواسطة‬ ‫والمفقودة‬ ‫المكتسبة‬ ‫الحرارة‬ ‫كمية‬
 Spontaneity of a reaction
.‫النظام‬ ‫تلقائية‬
11Dr. Wael A. El-Helece

12. Chemical
Thermodynamics
Chemical Thermodynamics
‫الحرارية‬ ‫الديناميكا‬ ‫كيمياء‬
 Gibbs free energy function
.‫الحرة‬ ‫للطاقة‬ ‫جبس‬ ‫دالة‬
 Relationship between Gibbs Free Energy and chemical
equilibrium
.‫الكيميائى‬ ‫والتزان‬ ‫الحرة‬ ‫جبس‬ ‫طاقة‬ ‫بين‬ ‫العلقة‬
12Dr. Wael A. El-Helece

13. Chemical
Thermodynamics
First Law of Thermodynamics
‫الحرارية‬ ‫للديناميكا‬ ‫الول‬ ‫القانون‬
• energy cannot be created nor destroyed.
•.‫العدم‬ ‫من‬ ‫تستحدث‬ ‫ول‬ ‫تفنى‬ ‫ل‬ ‫الطاقة‬
• Therefore, the total energy of the universe is a
constant.
•.‫ثابته‬ ‫للكون‬ ‫الكلية‬ ‫الطاقة‬ ‫فان‬ ‫وبالتالى‬
• Energy can, however, be converted from one form to
another or transferred from a system to the
surroundings or vice versa.
•‫الى‬ ‫نظام‬ ‫من‬ ‫وتنتقل‬ ‫اخرى‬ ‫الى‬ ‫صورة‬ ‫من‬ ‫تتحول‬ ‫ان‬ ‫يمكن‬ ‫الطاقة‬
.‫والعكس‬ ‫المحيط‬
13Dr. Wael A. El-Helece

14. Chemical
Thermodynamics
Conservation of Energy
‫الطاقة‬ ‫بقاء‬
• In interactions between a system and its surroundings
the total energy remains constant.
.‫ثابتة‬ ‫الطاقة‬ ‫كمية‬ ‫تظل‬ ‫ومحيطه‬ ‫النظام‬ ‫بين‬ (‫)التداخل‬ ‫التلمس‬ ‫عند‬
• energy is neither created nor destroyed.
.‫تستحدث‬ ‫ول‬ ‫تفنى‬ ‫ل‬ ‫الطاقة‬
qsystem + qsurroundings = 0 qsystem = -qsurroundings
14Dr. Wael A. El-Helece

15. Chemical
Thermodynamics
Spontaneous Processes
‫التلقائية‬ ‫العمليات‬
• Spontaneous processes proceed
without any outside intervention.
•‫اى‬ ‫دون‬ ‫تحدث‬ ‫التلقائية‬ ‫العمليات‬
.‫خارجى‬ ‫حث‬
• The gas in vessel B will
spontaneously effuse into vessel
A.
•) ‫الوعاء‬ ‫فى‬ ‫الغاز‬B‫إلى‬ ‫تلقائيا‬ ‫ينتقل‬ ‫(سوف‬
) ‫الوعاء‬A.(
15Dr. Wael A. El-Helece

16. Chemical
Thermodynamics
Spontaneous Processes
‫التلقائية‬ ‫العمليات‬
Processes that are spontaneous
in one direction are non-
spontaneous in the reverse
direction.
‫التجاهين‬ ‫دد‬‫د‬‫دد‬‫اح‬ ‫دىدد‬‫ف‬ ‫دةد‬‫ي‬‫التلقائ‬ ‫العمليات‬
.‫المعاكس‬ ‫التجاه‬ ‫فى‬ ‫لتلقائية‬ ‫تكون‬
16Dr. Wael A. El-Helece

17. Chemical
Thermodynamics
Spontaneous Processes
‫التلقائية‬ ‫العمليات‬
• Processes that are spontaneous at one temperature
may be nons-pontaneous at other temperatures.
•‫عند‬ ‫لتلقائية‬ ‫تكون‬ ‫ربما‬ ‫حرارة‬ ‫درجة‬ ‫عند‬ ‫التلقائية‬ ‫العمليات‬
.‫أخرى‬ ‫حرارة‬ ‫درجات‬
Ice
‫ثلج‬
Water
‫ماء‬
17Dr. Wael A. El-Helece

18. Chemical
Thermodynamics
Reversible Processes
‫النعكاسية‬ ‫العمليات‬
In a reversible process the system
changes in such a way that the system
and surroundings can be put back in
their original states by exactly
reversing the process.
‫التى‬ ‫بالطريققة‬ ‫يتغيقر‬ ‫النظام‬ ‫النعكاسقية‬ ‫العمليا ت‬ ‫فقى‬
‫الولية‬ ‫الحالة‬ ‫على‬ ‫والمحيط‬ ‫النظام‬ ‫يتواجد‬ ‫ان‬ ‫يمكن‬
.‫تماما‬ ‫العملية‬ ‫عكس‬ ‫طريق‬ ‫عن‬
18Dr. Wael A. El-Helece

19. Chemical
Thermodynamics
Irreversible Processes
‫النعكاسية‬ ‫غير‬ ‫العمليات‬
• Irreversible processes cannot be done by exactly
reversing the change to the system.
•‫فى‬ ‫بالضبط‬ ‫تتم‬ ‫أن‬ ‫يمكن‬ ‫ل‬ ‫النعكاسية‬ ‫غير‬ ‫العمليات‬
.‫الحادث‬ ‫التغير‬ ‫يعكس‬ ‫الذى‬ ‫التجاه‬
• Spontaneous processes are irreversible.
•.‫انعكاسية‬ ‫غير‬ ‫التلقائية‬ ‫العمليات‬
19Dr. Wael A. El-Helece

20. Chemical
Thermodynamics
Spontaneous reactions
‫التلقائية‬ ‫التفاعل ت‬
CH4 (g) + 2O2 (g) CO2 (g) + 2H2O (l) ∆H0
= -890.4 kJ
H+
(aq) + OH-
(aq) H2O (l) ∆H0
= -56.2 kJ
H2O (s) H2O (l) ∆H0
= 6.01 kJ
NH4NO3 (s) NH4
+
(aq) + NO3
-
(aq) ∆H0
= 25 kJH2O
20Dr. Wael A. El-Helece

21. Chemical
Thermodynamics
The First Law of Thermodynamics
‫الحرارية‬ ‫للديناميكا‬ ‫الول‬ ‫القانون‬
• Internal Energy, U. ‫الداخلية‬ ‫الطاقة‬
Total energy (potential and kinetic) in a system.
‫والحركة‬ ‫الوضع‬ ‫طاقتى‬ ‫مجموع‬
Translational kinetic energy. ‫انتقالية‬ ‫حركة‬ ‫.طاقة‬
Molecular rotation. ‫جزيئي‬ ‫تردد‬
Bond vibration. ‫الرابطة‬ ‫اهتزاز‬
Intermolecular attractions. ‫الجزيئا ت‬ ‫بين‬ ‫تجاذبا ت‬.
Chemical bonds. ‫الكيميائية‬ ‫الروابط‬
Electrons. ‫اللكترونا ت‬ ‫حركة‬
21Dr. Wael A. El-Helece

22. Chemical
Thermodynamics
Entropy
‫العشوائية‬ ‫مقياس‬
• Entropy (S) is a term coined by Rudolph Clausius in the
19th century.
‫فى‬ ‫كلسوسيوس‬ ‫رسودسولف‬ ‫بواسطة‬ ‫استخدامه‬ ‫تم‬ (‫)التنترسوبيا‬ ‫العشوائية‬ ‫مفهوم‬
.‫عشر‬ ‫التاسع‬ ‫القرن‬
• Clausius was convinced of the significance of the ratio
of heat delivered and the temperature at which it is
delivered.
‫سودرجة‬ ‫المنتقللة‬ ‫الحرارة‬ ‫كميلة‬ ‫ملن‬ ‫علةقلة‬ ‫بوجود‬ ‫مقتنعلا‬ ‫كان‬ ‫كلسوسليوس‬
.‫التنتقال‬ ‫عندها‬ ‫يحدث‬ ‫التي‬ ‫الحرارة‬q
T
22Dr. Wael A. El-Helece

23. Chemical
Thermodynamics
Entropy
‫العشوائية‬ ‫مقياس‬
• Entropy can be thought of as a measure of the
randomness of a system.
‫انه‬ ‫على‬ ‫اعتباره‬ ‫يمكن‬ ‫النتروبى‬‫للعشوائية‬ ‫مقياس‬‫داخل‬
.‫النظام‬
• It is related to the various modes of motion in
molecules.
.‫الجزيئات‬ ‫فى‬ ‫الحركة‬ ‫بأنواع‬ ‫اساسى‬ ‫بشكل‬ ‫مرتبط‬
• Like total energy, E, and enthalpy, H, entropy is a state
function. ‫سوكذا‬ ‫الكلية‬ ‫الطاةقة‬ ‫مثل‬ ‫مثله‬ ‫حالة‬ ‫دالة‬ ‫التنترسوبى‬‫المحتوى‬
‫الحراري‬
• Therefore, 23Dr. Wael A. El-Helece

24. Chemical
Thermodynamics
Entropy
‫العشوائية‬ ‫مقياس‬
For a process occurring at constant temperature (an
isothermal process), the change in entropy is equal to
the heat that would be transferred if the process were
reversible divided by the temperature.
‫المنتقلة‬ ‫الحرارة‬ ‫بكمية‬ ‫لنظام‬ ‫النتروبيا‬ ‫فى‬ ‫التغير‬ ‫يقدر‬
.‫انعكاسية‬ ‫العملية‬ ‫كانت‬ ‫إذا‬ ‫الحرارة‬ ‫درجة‬ ‫على‬ ‫مقسومة‬
∆S =
qrev
T
24Dr. Wael A. El-Helece

25. Chemical
Thermodynamics
Entropy (S) = a measure of randomness or disorder
MATTER IS ENERGY.
ENERGY IS INFORMATION.
EVERYTHING IS INFORMATION.
PHYSICS SAYS THAT STRUCTURES...
BUILDINGS, SOCIETIES,
IDEOLOGIES... WILL SEEK THEIR
POINT OF LEAST ENERGY.
THIS MEANS THAT
THINGS FALL.
THEY FALL FROM HEIGHTS OF
ENERGY AND STRUCTURED
INFORMATION INTO
MEANINGLESS, POWERLESS
DISORDER.
THIS IS CALLED
ENTROPY.

26. Chemical
Thermodynamics
Entropy
‫النتروبيا‬
• To predict spontaneity we need: ‫تنحتاج‬ ‫التلقائية‬ ‫تنعين‬ ‫لكي‬
Change in enthalpy ‫الحراري‬ ‫المحتوى‬ ‫في‬ ‫التغير‬
Entropy ‫العشوائية‬ ‫)مقياس‬ ‫)التنترسوبيا‬
Entropy- a measure of the randomness or disorder
of a system.
‫النظام‬ ‫فى‬ ‫سوالفوضى‬ ‫العشوائية‬ ‫مقياس‬ ‫التنترسوبيا‬
↑ Disorder ‫الفوضى‬ = ↑ Entropy ‫التنترسوبيا‬
26Dr. Wael A. El-Helece

27. Chemical
Thermodynamics
Entropy and Disorder ‫سوالعشوائية‬ ‫التنترسوبيا‬
27Dr. Wael A. El-Helece

28. Chemical
Thermodynamics
Entropy on the Molecular Scale
‫الجزيئي‬ ‫المستوى‬ ‫على‬ ‫النتروبيا‬
• Ludwig Boltzmann described the concept of entropy on
the molecular level.
.‫الجزيئي‬ ‫المستوى‬ ‫على‬ ‫النتروبيا‬ ‫مفهوم‬ ‫شرح‬ ‫بولتزمان‬
• Temperature is a measure of the average kinetic energy
of the molecules in a sample.
.‫العينة‬ ‫فى‬ ‫للجزيئات‬ ‫الحركة‬ ‫طاةقة‬ ‫لمتوسط‬ ‫مقياس‬ ‫الحرارة‬ ‫درجة‬
28Dr. Wael A. El-Helece

29. Chemical
Thermodynamics
Entropy on the Molecular Scale
‫الجزيئي‬ ‫المستوى‬ ‫على‬ ‫النتروبيا‬
• Molecules exhibit several types of motion:
:‫الحركة‬ ‫أنواع‬ ‫من‬ ‫نوع‬ ‫من‬ ‫أكثر‬ ‫على‬ ‫تحتوى‬ ‫الجزيئات‬
 Translational: Movement of the entire molecule from one place to
another. ‫من‬ ‫للجزيئ‬ ‫انتقال‬ ‫يحدث‬ ‫انتقالية‬ ‫حركة‬
‫لخر‬ ‫مكان‬
 Vibrational: Periodic motion of atoms within a molecule.
‫الجزيئ‬ ‫داخل‬ ‫للذرات‬ ‫دورية‬ ‫حركة‬ ‫اهتزازية‬ ‫حركة‬
 Rotational: Rotation of the molecule on about an axis or rotation
about σ bonds. ‫احد‬ ‫حول‬ ‫ككل‬ ‫الجزيئ‬ ‫دوران‬ ‫دورانية‬ ‫حركة‬
‫المحاور‬
29Dr. Wael A. El-Helece

30. Chemical
Thermodynamics
Microstates and Entropy ‫سوالتنترسوبي‬ ‫الداخلية‬ ‫التغيرات‬
• Boltzmann, 1868 ‫بولتزمان‬
S = k ln W
• k = 1.38 x 10-23
J/K
↑ W = ↑ Entropy
∆ S = Sf – Si
∆ S = k ln Wf
Wi
30Dr. Wael A. El-Helece

31. Chemical
Thermodynamics
Entropy on the Molecular Scale
‫الجزيئى‬ ‫المقياس‬ ‫على‬ ‫التنترسوبيا‬
• Each thermodynamic state has a specific number of
microstates, W, associated with it.
.‫لها‬ ‫مصاحبة‬ ‫الشغل‬ ‫من‬ ‫محدد‬ ‫عدد‬ ‫لها‬ ‫حرارية‬ ‫ديناميكا‬ ‫حالة‬ ‫كل‬
• Entropy is ‫هو‬ ‫النتروبيا‬
S = k lnW
where k is the Boltzmann constant, 1.38 × 10−23
J/K.
) ‫أن‬ ‫حيث‬k. (‫بولتزمان‬ ‫ثابت‬ ‫هو‬
31Dr. Wael A. El-Helece

32. Chemical
Thermodynamics
Entropy on the Molecular Scale
‫الجزيئى‬ ‫المقياس‬ ‫على‬ ‫التنترسوبيا‬
• The change in entropy for a process, then, is
‫يكون‬ ‫ما‬ ‫لعملية‬ ‫النتروبيا‬ ‫فى‬ ‫التغير‬
∆S = k lnWfinal − k lnWinitial
Wfinal
Winitial
∆S ∆S = k ln
• Entropy increases with the number of microstates
in the system. ‫للمادة‬ ‫الداخلية‬ ‫العوامل‬ ‫بزيادة‬ ‫التنترسوبى‬ ‫يزداد‬
32Dr. Wael A. El-Helece

33. Chemical
Thermodynamics
Entropy on the Molecular Scale
‫الجزيئى‬ ‫المقياس‬ ‫على‬ ‫التنترسوبيا‬
• The number of microstates and, therefore, the entropy
tends to increase with increases in
‫بزيادة‬ ‫تزداد‬ ‫العشوائية‬ ‫سوبالتالي‬ ‫الداخلية‬ ‫العوامل‬ ‫عدد‬
Temperature. ‫الحرارة‬ ‫درجة‬
Volume. ‫الحجم‬
The number of independently moving molecules.
.‫عشوائيا‬ ‫تتحرك‬ ‫التي‬ ‫الجزيئات‬ ‫عدد‬
33Dr. Wael A. El-Helece

34. Chemical
Thermodynamics
Entropy and Physical States
‫الجزيئى‬ ‫المقياس‬ ‫على‬ ‫التنترسوبيا‬
• Entropy increases with
the freedom of motion of
molecules.
‫حرية‬ ‫بزيادة‬ ‫تزداد‬ ‫النتروبيا‬
‫للجزيئات‬ ‫الحركة‬
• Therefore, ‫وبالتالى‬
S(g) > S(l) > S(s)
34Dr. Wael A. El-Helece

35. Chemical
Thermodynamics
Solutions ‫المحاليل‬
Generally, when a
solid is dissolved in a
solvent, entropy
increases.
,‫صلب‬ ‫يذاب‬ ‫عندما‬ ‫عموما‬
. ,‫تزداد‬ ‫النتروبيا‬ ‫مذيب‬ ‫في‬
35Dr. Wael A. El-Helece

36. Chemical
Thermodynamics
Entropy Changes
‫التنترسوبيا‬ ‫تغيرات‬
• In general, entropy increases when
,‫عندما‬ ‫يزداد‬ ‫النتروبيا‬ ‫عموما‬
 Gases are formed from liquids
and solids.
.‫والصلب‬ ‫السوائل‬ ‫من‬ ‫الغازات‬ ‫تتكون‬
 Liquids or solutions are formed
from solids.
‫الصلب‬ ‫من‬ ‫تتكون‬ ‫والمحاليل‬ ‫السوائل‬
 The number of gas molecules
increases.
‫تزداد‬ ‫الغاز‬ ‫جزيئات‬ ‫عدد‬
 The number of moles
increases.
.‫المولت‬ ‫عدد‬ ‫تزداد‬
36Dr. Wael A. El-Helece

37. Chemical
Thermodynamics
Second Law of Thermodynamics
‫الحرارية‬ ‫للديناميكا‬ ‫الثانى‬ ‫القانون‬
The second law of thermodynamics states that:
:‫على‬ ‫الحرارية‬ ‫للديناميكا‬ ‫الثاتني‬ ‫القاتنون‬ ‫ينص‬
The entropy of the universe increases for spontaneous
processes.
.‫التلقائية‬ ‫للعمليات‬ (‫المحيط‬ + ‫)النظام‬ ‫الكون‬ ‫في‬ ‫التنترسوبيا‬ ‫تزداد‬
The entropy of the universe does not change for
reversible processes.
.‫التنعكاسية‬ ‫للعمليات‬ ‫الكون‬ ‫في‬ ‫التنترسوبيا‬ ‫يتأثر‬ ‫ل‬
37Dr. Wael A. El-Helece

38. Chemical
Thermodynamics
Second Law of Thermodynamics
‫الحرارية‬ ‫للديناميكا‬ ‫الثانى‬ ‫القانون‬
In other words: ‫اخرى‬ ‫بعبارات‬
For reversible processes: ‫التنعكاسية‬ ‫للعمليات‬
∆Suniv = ∆Ssystem + ∆Ssurroundings = 0
For irreversible processes: ‫التنعكاسية‬ ‫غير‬ ‫للعمليات‬
∆Suniv = ∆Ssystem + ∆Ssurroundings > 0
38Dr. Wael A. El-Helece

39. Chemical
Thermodynamics
Second Law of Thermodynamics
‫الحرارية‬ ‫للديناميكا‬ ‫الثانى‬ ‫القانون‬
These last truths mean that as a result of all
spontaneous processes the entropy of the
universe increases.
‫العمليات‬ ‫لكل‬ ‫ةة‬‫ة‬‫ةة‬‫نتيج‬ ‫ةنة‬‫أ‬ ‫ةىة‬‫ن‬‫تع‬ ‫الخيرة‬ ‫ةقة‬‫ئ‬‫الحقا‬ ‫هذه‬
.‫تزداد‬ ‫الكون‬ ‫عشوائية‬ ‫التلقائية‬
39Dr. Wael A. El-Helece

40. Chemical
Thermodynamics
Standard Entropies ‫القياسية‬ ‫النتروبيا‬
• These are molar entropy values
of substances in their standard
states.
•‫المواد‬ ‫لبعض‬ ‫النوعية‬ ‫النتروبيا‬ ‫قيم‬ ‫هذه‬
.‫القياسية‬ ‫حالتها‬ ‫فى‬
• Standard entropies tend to
increase with increasing molar
mass.
•‫بزيادة‬ ‫تزداد‬ ‫القياسية‬ ‫ةةة‬‫ي‬‫النوع‬ ‫ةاة‬‫ي‬‫النتروب‬
.‫النوعية‬ ‫الكتلة‬
40Dr. Wael A. El-Helece

41. Chemical
Thermodynamics
Standard Entropies ‫القياسية‬ ‫النتروبيا‬
Larger and more complex molecules
have greater entropies.
‫النتروبيا‬ ‫قيمة‬ ‫تكون‬ ‫تعقيدا‬ ‫والكثر‬ ‫الكبر‬ ‫الجزيئات‬
.‫كبيرة‬
41Dr. Wael A. El-Helece

42. Chemical
Thermodynamics
Entropy Changes ‫النتروبيا‬ ‫تغير‬
Entropy changes for a reaction can be estimated in a manner
analogous to that by which ∆H is estimated:
‫فى‬ ‫التغير‬ ‫تعين‬ ‫يتم‬ ‫للتى‬ ‫مشابهه‬ ‫بطريقة‬ ‫تعينها‬ ‫يمكن‬ ‫لتفاعل‬ ‫التنترسوبيا‬ ‫تغيرات‬
.‫الحراري‬ ‫المحتوى‬
∆S° = Σn∆S°(products) - Σm∆S°(reactants)
where n and m are the coefficients in the
balanced chemical equation.
‫ان‬ ‫حيث‬n‫و‬m‫الكيميائية‬ ‫المعادلة‬ ‫في‬ ‫معاملت‬ 42Dr. Wael A. El-Helece

43. Chemical
Thermodynamics
Entropy Changes in Surroundings
‫المحيطات‬ ‫انتروبيا‬ ‫فى‬ ‫التغيرات‬
• Heat that flows into or out of the system changes the
entropy of the surroundings.
•.‫للمحيط‬ ‫النتروبيا‬ ‫تغير‬ ‫النظام‬ ‫عبر‬ ‫او‬ ‫من‬ ‫تنساب‬ ‫التى‬ ‫الحرارة‬
• For an isothermal process:
•:‫حراريا‬ ‫المعزولة‬ ‫للعمليات‬
∆Ssurr = −qsys
T
• At constant pressure, qsys is simply ∆H° for the
system. ‫التغير‬ ‫تبسيطا‬ ‫هى‬ ‫نظام‬ ‫حرارة‬ ‫ثابت‬ ‫ضغط‬ ‫عند‬
‫النثالبى‬ ‫فى‬ 43Dr. Wael A. El-Helece

44. Chemical
Thermodynamics
Entropy Change in the Universe
‫الكون‬ ‫انتروبيا‬ ‫فى‬ ‫التغيرات‬
• The universe is composed of the system
and the surroundings.
•.‫والمحيط‬ ‫النظام‬ ‫من‬ ‫يتكون‬ ‫الكون‬
• Therefore, ‫وبالتالي‬
∆Suniverse = ∆Ssystem + ∆Ssurroundings
• For spontaneous processes ‫للعمليات‬
‫التلقائية‬
∆Suniverse > 0 44Dr. Wael A. El-Helece

45. Chemical
Thermodynamics
Entropy Change in the Universe
‫الكون‬ ‫انتروبيا‬ ‫فى‬ ‫التغيرات‬
• This becomes:
∆Suniverse = ∆Ssystem +
Multiplying both sides by −T,
−T∆Suniverse = ∆Hsystem − T∆Ssystem
−∆Hsystem
T
45Dr. Wael A. El-Helece

46. Chemical
Thermodynamics
Gibbs Free Energy
‫الحرة‬ ‫للطاقة‬ ‫جبس‬ ‫دالة‬
∀−TΔSuniverse is defined as the Gibbs free energy, ∆G. ‫ةلادالة‬
‫فى‬ ‫مضروبا‬ ‫النظام‬ ‫انتروبيا‬ ‫فى‬ ‫التغير‬ ‫تساوى‬ ‫الحرة‬ ‫للطاقة‬ ‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجبس‬
‫الحرارة‬ ‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجة‬‫ر‬‫ةلاد‬
∆G = −TΔSuniverse
• When ∆Suniverse is positive, ∆G is negative.
•.‫سالبة‬ ‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجبس‬ ‫ةلادالة‬ ‫تكون‬ ‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجبة‬‫و‬‫م‬ ‫النظام‬ ‫انتروبيا‬ ‫تكون‬ ‫عندما‬
• Therefore, when ∆G is negative, a process is
spontaneous.
•‫تلقائية‬ ‫تكون‬ ‫العملية‬ ,‫سالبة‬ ‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجبس‬ ‫ةلادالة‬ ‫تكون‬ ‫عندما‬ ,‫وبالتالي‬46Dr. Wael A. El-Helece

47. Chemical
Thermodynamics
Dr. Wael A. El-Helece 47

48. Chemical
Thermodynamics
Gibbs Free Energy
‫الحرة‬‫جبس‬ ‫دالة‬
1. If ΔG is negative, the forward reaction is spontaneous.
.‫تلقائي‬ ‫يكون‬ ‫ةلادى‬‫ر‬‫الط‬ ‫التفاعل‬ ,‫سالبة‬ ‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجبس‬ ‫ةلادالة‬ ‫قيمة‬ ‫كانت‬ ‫اذا‬
2. If ΔG is 0, the system is at equilibrium.
.‫التزان‬ ‫عند‬ ‫يكون‬ ‫التفاعل‬ ,‫صفر‬ ‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجبس‬ ‫ةلادالة‬ ‫قيمة‬ ‫كانت‬ ‫اذا‬
3. If ∆G is positive, the reaction is spontaneous in the reverse
direction.
.‫تلقائي‬ ‫يكون‬ ‫العكسي‬ ‫التفاعل‬ ,‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجبة‬‫و‬‫م‬ ‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجبس‬ ‫ةلادالة‬ ‫قيمة‬ ‫كانت‬ ‫اذا‬
48Dr. Wael A. El-Helece

49. Chemical
Thermodynamics
Reaction Quotient ‫التفاعل‬ ‫حاصل‬
the reaction quotient (Q) is equal to the equilibrium constant (k).
.‫التزان‬ ‫ظروف‬ ‫غير‬ ‫فى‬ ‫التزان‬ ‫لثابت‬ ‫مساويا‬ ‫يكون‬ ‫التفاعل‬ ‫حاصل‬
We can write the reaction quotient Q for any half reaction in terms of the
activities of the species:
.‫التفكك‬ ‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجة‬‫ر‬‫ةلاد‬ ‫بدللة‬ ‫تفاعل‬ ‫نصف‬ ‫ل ي‬ ‫التفاعل‬ ‫حاصل‬ ‫كتابة‬ ‫يمكننا‬
Note: electrons do not appear in the reaction quotient.
.‫التفاعل‬ ‫حاصل‬ ‫فى‬ ‫اللكترونات‬ ‫تظهر‬ ‫ل‬ :‫لحظ‬
(a=1 for pure solids and liquids so they do not appear).
= ‫الكفاءة‬1.‫النقية‬ ‫والسوائل‬ ‫الصلبة‬ ‫ةلاد‬‫ا‬‫للمو‬Dr. Elhelece W. A.

50. Chemical
Thermodynamics
Dr. Elhelece W. A. 50
Calculating the Reaction Quotient, Q ‫التفاعل‬ ‫حاصل‬ ‫حساب‬
Q can be calculated for any set of conditions, not just for equilibrium.
.‫التزان‬ ‫عند‬ ‫فقط‬ ‫ليس‬ ‫ظروف‬ ‫اى‬ ‫عند‬ ‫التفاعل‬ ‫حاصل‬ ‫حساب‬ ‫يمكن‬
Q can be used to determine which direction a reaction will shift to reach equilibrium.
.‫التزان‬ ‫الى‬ ‫التفاعل‬ ‫يزيح‬ ‫ان‬ ‫يمكن‬ ‫اتجاه‬ ‫اى‬ ‫فى‬ ‫يوضح‬ ‫ان‬ ‫يمكن‬ ‫التفاعل‬ ‫حاصل‬
If K > Q, a reaction will proceed forward, converting reactants into products.
‫قيمة‬ ‫كانت‬ ‫اذا‬K‫قيمة‬ ‫من‬ ‫أكبر‬Q.‫نواتج‬ ‫الى‬ ‫المتفاعلت‬ ‫تحويل‬ ,‫ةلادى‬‫ر‬‫الط‬ ‫التجاه‬ ‫فى‬ ‫يسير‬ ‫التفاعل‬
If K < Q, the reaction will proceed in the reverse direction, converting products into
reactants.
‫قيمة‬ ‫كانت‬ ‫اذا‬Q‫قيمة‬ ‫من‬ ‫أكبر‬K.‫متفاعلت‬ ‫الى‬ ‫النواتج‬ ‫تحويل‬ ,‫العكسي‬ ‫التجاه‬ ‫فى‬ ‫يسير‬ ‫التفاعل‬
If Q = K then the system is already at equilibrium.
‫قيمة‬ ‫كانت‬ ‫اذا‬Q‫قيمة‬ ‫تساوى‬K.‫التزان‬ ‫عند‬ ‫يكون‬ ‫التفاعل‬
Reaction Quotient ‫التفاعل‬ ‫حاصل‬

51. Chemical
Thermodynamics
Dr. Elhelece W. A.
In order to determine Q we need to know:
:‫نعرف‬ ‫ان‬ ‫يجب‬ ‫التفاعل‬ ‫حاصل‬ ‫قيمة‬ ‫لحساب‬
the equation for the reaction, including the physical states,
,‫الفزيائية‬ ‫الحالة‬ ‫متضمنة‬ ‫التفاعل‬ ‫ةلادلة‬‫ا‬‫مع‬
the quantities of each species (molarities and/or pressures),
.(‫الضغوط‬ ‫او‬ ‫)المولرية‬ ‫المختلفة‬ ‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجزاء‬‫ل‬‫ا‬ ‫كميات‬
all measured at the same moment in time.
.‫الزمن‬ ‫من‬ ‫اللحظة‬ ‫نفس‬ ‫عند‬ ‫كلها‬ ‫مقاسة‬
To calculate Q:
‫لحساب‬Q:
1. Write the expression for the reaction quotient.
.‫التفاعل‬ ‫حاصل‬ ‫لحساب‬ (‫)الصيغة‬ ‫القانون‬ ‫اكتب‬
2. Find the molar concentrations or partial pressures of each species involved.
.‫التفاعل‬ ‫فى‬ ‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجزء‬ ‫لكل‬ ‫الجزيئية‬ ‫الضغوط‬ ‫او‬ ‫المولر ي‬ ‫التركيز‬ ‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجد‬‫و‬‫ا‬
3. Substitute values into the expression and solve.
.‫وحل‬ ‫الصيغة‬ ‫فى‬ ‫القيم‬ ‫ةلادخل‬‫ا‬
Reaction Quotient ‫التفاعل‬ ‫حاصل‬

52. Chemical
Thermodynamics
Dr. Elhelece W. A.
Example: 0.035 moles of SO2
, 0.500 moles of SO2
Cl2
, and 0.080 moles of Cl2
are
combined in an evacuated 5.00 L flask and heated to 100o
C. What is Q before the
reaction begins? Which direction will the reaction proceed in order to establish
equilibrium?
SO2
Cl2
(g) SO2
(g) + Cl2
(g) Kc
= 0.078 at 100o
C
•Write the expression to find the reaction quotient, Q.
Since Kc is given, the amounts must be expressed as moles per
liter (molarity).
The amounts are in moles so a conversion is required.
0.500 mole SO2Cl2/5.00 L = 0.100 M SO2Cl2
0.035 mole SO2/5.00 L = 0.070 M SO2
0.080 mole Cl2/5.00 L = 0.016 M Cl2
Reaction Quotient ‫التفاعل‬ ‫حاصل‬

53. Chemical
Thermodynamics
Dr. Elhelece W. A. 53
Substitute the values in to the expression and solve for Q.
Compare the answer to the value for the equilibrium constant and predict
the shift.
0.078 (K) > 0.011 (Q)
Since K >Q, the reaction will proceed in the forward direction in order to
increase the concentrations of both SO2 and Cl2 and decrease that of
SO2Cl2 until Q = K.
Reaction Quotient ‫التفاعل‬ ‫حاصل‬

54. Chemical
Thermodynamics
Standard Free Energy Changes
‫القياسية‬ ‫الحرة‬ ‫الطاقة‬ ‫تغيرات‬
Analogous to standard enthalpies of formation are
standard free energies of formation, ∆Gf°.
.‫القياسية‬ ‫الحرة‬ ‫الطاقة‬ ‫تغيرات‬ ,‫القياسية‬ ‫التكوين‬ ‫طاقات‬ ‫مع‬ ‫متوافق‬
∆G° = Σn∆G°(products) − Σm∆G°(reactants)
f f
where n and m are the stoichiometric coefficients.
‫أن‬ ‫حيث‬n‫و‬m.‫التركيبية‬ ‫النسب‬ ‫عوامل‬
54Dr. Wael A. El-Helece

55. Chemical
Thermodynamics
Free Energy Changes
‫الحرة‬ ‫الطاقة‬ ‫تغيرات‬
At temperatures other than 25°C,
•‫غير‬ ‫حرارة‬ ‫درجات‬ ‫عند‬25,‫مئوية‬ ‫درجة‬
∆G° = ∆H° − T∆S°
How does ∆G° change with temperature?
‫درجة‬ ‫مع‬ ‫لنظام‬ ‫القياسية‬ ‫الحرة‬ ‫الطاقة‬ ‫تتغير‬ ‫أن‬ ‫يمكن‬ ‫كيف‬
‫الحرارة؟‬55Dr. Wael A. El-Helece

56. Chemical
Thermodynamics
Free Energy and Temperature
‫الحرارة‬ ‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجة‬‫ر‬‫ةلاد‬‫و‬ ‫الحرة‬ ‫الطاقة‬
• There are two parts to the free energy equation:
:‫الحرة‬ ‫الطاقة‬ ‫ةلادلة‬‫ا‬‫لمع‬ ‫نصفين‬ ‫هناك‬
∆H°— the enthalpy term ‫التكوين‬ ‫حرارات‬ ‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجزء‬
T∆S° — the entropy term ‫العشوائية‬ ‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجزء‬
• The temperature dependence of free energy, then
comes from the entropy term.
•‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجزء‬ ‫من‬ ‫تتأتى‬ ‫وبالتالي‬ ,‫الحرارة‬ ‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجة‬‫ر‬‫ةلاد‬ ‫على‬ ‫ةلادها‬‫ا‬‫واعتم‬ ‫الحرة‬ ‫الطاقة‬
.‫العشوائية‬
56Dr. Wael A. El-Helece

57. Chemical
Thermodynamics
Free Energy and Temperature
‫الحرارة‬ ‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجة‬‫ر‬‫ةلاد‬‫و‬ ‫الحرة‬ ‫الطاقة‬
57Dr. Wael A. El-Helece

58. Chemical
Thermodynamics
Free Energy and Equilibrium
‫والتزان‬ ‫الحرة‬ ‫الطاقة‬
Under any conditions, standard or nonstandard, the
free energy change can be found this way:
‫يمكن‬ ‫الحرة‬ ‫الطاقة‬ ‫فى‬ ‫التغير‬ ,‫قياسية‬ ‫غير‬ ‫أو‬ ‫قياسية‬ ‫ظروف‬ ‫أ ي‬ ‫تحت‬
:‫العلقة‬ ‫من‬ ‫يحسب‬ ‫أن‬
∆G = ∆G° + RT lnQ
(Under standard conditions, all concentrations are 1 M, so Q = 1 and lnQ
= 0; the last term drops out.)
‫التركيزات‬ ‫كل‬ ,‫القياسية‬ ‫الظروف‬ ‫فى‬1‫التفاعل‬ ‫حاصل‬ ‫وكذا‬ ‫مولر‬Q 1‫الخير‬ ‫الجزء‬ ‫وبالتالي‬
.‫يتليشي‬ ‫ةلادلة‬‫ا‬‫المع‬ ‫فى‬
58Dr. Wael A. El-Helece

59. Chemical
Thermodynamics
Free Energy and Equilibrium
‫والتزان‬ ‫الحرة‬ ‫الطاقة‬
• At equilibrium, Q = K, and ∆G = 0. ‫التزان‬ ‫عند‬
• The equation becomes ‫تصبح‬ ‫ةلادلة‬‫ا‬‫المع‬
0 = ∆G° + RT lnK
• Rearranging, this becomes ‫تصبح‬ ‫الترتيب‬ ‫ةلادة‬‫ا‬‫بإع‬
∆G° = −RT lnK
or, K = e−∆G°/RT
59Dr. Wael A. El-Helece

60. Chemical
Thermodynamics
In any spontaneous process, the entropy of the universe increases.
.‫ةلاد‬‫ا‬‫ةلاد‬‫ز‬‫ت‬ ‫للكون‬ ‫النتروبيا‬ ,‫تلقائية‬ ‫عملية‬ ‫ل ي‬
ΔSuniverse > 0
Another version of the 2nd
Law: ‫الثاني‬ ‫للقانون‬ ‫آخر‬ ‫يشكل‬
Energy spontaneously spreads out if it has no outside resistance.
.‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجية‬‫ر‬‫خا‬ ‫مقاومة‬ ‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجد‬‫و‬‫ي‬ ‫لم‬ ‫اذا‬ ‫النظام‬ ‫خارج‬ ‫تنتشر‬ ‫تلقائيا‬ ‫الطاقة‬
Entropy measures the spontaneous dispersal of energy as a function
of temperature ‫الحرارة‬ ‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجة‬‫ر‬‫ةلاد‬ ‫فى‬ ‫كدالة‬ ‫التلقائئي‬ ‫الطاقة‬ ‫انتشار‬ ‫يقيس‬ ‫النتروبيا‬
How much energy is spread out? ‫النظام‬ ‫خارج‬ ‫الطاقة‬ ‫انتشار‬ ‫مقدار‬ ‫ما‬
How widely spread out it becomes? ‫النظام‬ ‫خارج‬ ‫الطاقة‬ ‫انتشار‬ ‫مدى‬ ‫ما‬
Entropy change = “energy dispersed”/T ‫يساوى‬ ‫النتروبيا‬ ‫فى‬ ‫التغير‬
‫الحرارة‬ ‫ىف ابورضم ماظنلا ايبورتنا ىف ريغتلا ىواست ةرحلا ةقاطلل سبجة‬‫ر‬‫ةلاد‬ ‫على‬ ‫مقسوما‬ ‫الطاقة‬ ‫.انتشار‬
Second Law of Thermodynamics
‫الحرارية‬ ‫للديناميكا‬ ‫الثاني‬ ‫القانون‬
occurs without outside intervention
‫خارجي‬ ‫تأثير‬ ‫دون‬ ‫تحدث‬
↓

61. Chemical
Thermodynamics
Entropy of the Universe
‫الكون‬ ‫فى‬ ‫العشوائية‬
ΔSuniverse = ΔSsystem + ΔSsurroundings
Positional disorder
‫موضعي‬ ‫انتظام‬ ‫ل‬
Energetic disorder
‫الطاقة‬ ‫بسب‬ ‫انتظام‬ ‫ل‬
ΔSuniverse > 0 ⇒ spontaneous process ‫تلقائية‬ ‫عمليات‬
Both ΔSsys and ΔSsurr positive
Both ΔSsys and ΔSsurr negative
ΔSsys negative, ΔSsurr positive
ΔSsys positive, ΔSsurr negative
spontaneous process.
nonspontaneous process.
depends
depends

62. Chemical
Thermodynamics
Entropy of the Surroundings
(Energetic Disorder)
System
Heat Entropy
Surroundings
System
Heat Entropy
Surroundings
T
ΔH
ΔS
sys
surr −=
Low T ⇒ large entropy change (surroundings)
High T ⇒ small entropy change (surroundings)
ΔHsys < 0
ΔHsys > 0
ΔSsurr > 0
ΔSsurr < 0

63. Chemical
Thermodynamics
Positional Disorder and Probability
‫والحتمالت‬ ‫موضعى‬ ‫انتظام‬ ‫ل‬
Probability of 1 particle in left bulb = ½
" 2 particles both in left bulb = (½)(½) = ¼
" 3 particles all in left bulb = (½)(½)(½) = 1/8
" 4 " all " = (½)(½)(½)(½) = 1/16
" 10 " all " = (½)10
= 1/1024
" 20 " all " = (½)20
= 1/1048576
" a mole of " all " = (½)6.02×10
23
The arrangement with the greatest entropy is the one

64. Chemical
Thermodynamics
Ssolid < Sliquid << Sgas
Entropy of the System: Positional Disorder
Ordered
states
Disordered
states
Low probability
(few ways)
High probability
(many ways)
Low S
High S
Ssystem ∝ Positional disorder
S increases with increasing # of possible positions
Ludwig Boltzmann

65. Chemical
Thermodynamics
Entropy Curve
Solid GasLiquid
S
(qrev/T)
(J/K)
Temperature (K)
0
0
← fusion
← vaporization
S° (absolute entropy) can be calculated for any substance

66. Chemical
Thermodynamics
Entropy Increases with...
• Melting (fusion) Sliquid > Ssolid
ΔHfusion/Tfusion = ΔSfusion
• Vaporization Sgas > Sliquid
ΔHvaporization/Tvaporization = ΔSvaporization
• Increasing ngas in a reaction
• Heating ST2 > ST1 if T2 > T1
• Dissolving (usually) Ssolution > (Ssolvent + Ssolute)
• Molecular complexity more bonds, more entropy
• Atomic complexity more e-
, protons, neutrons

67. Chemical
Thermodynamics
Characteristics of Entropy
‫العشوائية‬ ‫مقياس‬ ‫خصائص‬
• S is a state function ‫حالة‬ ‫دالة‬ ‫التنتروبيا‬
• S is extensive (more stuff, more entropy) ‫مركزة‬ ‫غير‬ ‫خاصية‬
• At 0 K, S = 0 (we can know absolute entropy) ‫عند‬ ‫المطلقة‬ ‫التنتروبيا‬
‫المطلقة‬ ‫الحرارة‬ ‫درجة‬
• S > 0 for elements and compounds in their standard states
‫القياسية‬ ‫حالهتها‬ ‫فى‬ ‫والمركبات‬ ‫للعناصر‬ ‫الصفر‬ ‫من‬ ‫اكبر‬ ‫التنتروبيا‬
• ΔS°rxn = ΣnS°products - ΣnS°reactants
• Raise T → increase S ‫التنتروبيا‬ ‫هتزداد‬ ‫الحرارة‬ ‫درجة‬ ‫بارهتفاع‬
• Increase ngas → increase S ‫العشوائية‬ ‫هتزداد‬ ‫المولت‬ ‫عدد‬ ‫بزيادة‬
• More complex systems ⇒ larger S ‫قيمة‬ ‫اكبر‬ ‫عشوائي‬ ‫هتعقيدا‬ ‫اكثر‬ ‫تنظام‬

68. Chemical
Thermodynamics
by Mike Roller

69. Chemical
Thermodynamics
Entropy (S) Review• ΔSuniverse > 0 for spontaneous processes
• ΔSuniverse = ΔSsystem + ΔSsurroundings
↑
positional
↑
energetic
• We can know the absolute entropy value for a substance
• S° values for elements & compounds in their standard
states are tabulated (Appendix C, p. 1019)
• For any chemical reaction, we can calculate ΔS°rxn:
• ΔS°rxn = ΣS°(products) - ΣS°(reactants)

70. Chemical
Thermodynamics
ΔSuniverse and Chemical Reactions
ΔSuniverse = ΔSsystem + ΔSsurroundings
For a system of reactants and products,
ΔSuniverse = ΔSrxn – ΔHrxn/T
• If ΔSuniverse > 0, the reaction is spontaneous
• If ΔSuniverse < 0, the reaction is not spontaneous
– The reverse reaction is spontaneous
• If ΔSuniverse = 0, the reaction is at equilibrium
– Neither the forward nor the reverse reaction is favored

71. Chemical
Thermodynamics
C6H12O6(s) + 6 O2(g) → 6 CO2(g) + 6 H2O(g)
Compound
C6H12O6(s)
O2(g)
CO2(g)
H2O(g)
ΔH°f (kJ/mol)
-1275
0
-393.5
-242
S° (J/mol K)
212
205
214
189
ΔSuniverse = ΔSrxn – ΔHrxn/T
ΔS°rxn = ΣS°(products) - ΣS°(reactants)
= [6 S°(CO2(g)) + 6 S°(H2O(g))] – [S°(C6H12O6(s)) + 6 S°(O2(g))]
= [6(214) + 6(189)] – [(212) + 6(205)] J/K
ΔS°rxn = 976 J/K
ΔH°rxn = ΣΔH°f (products) - ΣΔH°f(reactants)
= [6 ΔH°f(CO2(g)) + 6 ΔH°f(H2O(g))] – [ΔH°f(C6H12O6(s)) + 6 ΔH°f(O2(g))]
= [6(-393.5) + 6(-242)] – [(-1275) + 6(0)] kJ

72. Chemical
Thermodynamics
C6H12O6(s) + 6 O2(g) → 6 CO2(g) + 6 H2O(g)
Compound
C6H12O6(s)
O2(g)
CO2(g)
H2O(g)
ΔH°f (kJ/mol)
-1275
0
-393.5
-242
S° (J/mol K)
212
205
214
189
ΔSuniverse = ΔSrxn – ΔHrxn/T
ΔS°rxn = 976 J/K (per mole of glucose)
ΔH°rxn = -2538 kJ (per mole of glucose)
At 298 K,
ΔS°universe = 0.976 kJ/K – (-2538 kJ/298 K)
ΔS°universe = 9.5 kJ/K

73. Chemical
Thermodynamics
–ΔG means +ΔSuniv
A process (at constant T, P) is
spontaneous if free energy decreases
Gibbs Free Energy
(G)
Josiah Gibbs
G = H – TS
At constant temperature,
ΔG = ΔH – TΔS
(system’s point of view)
ΔG = ΔH – TΔS
Divide both sides by –T
-ΔG/T = -ΔH/T + ΔS
ΔSuniverse = ΔS – ΔH/T

74. Chemical
Thermodynamics
ΔG and Chemical Reactions
ΔG = ΔH – TΔS
• If ΔG < 0, the reaction is spontaneous
• If ΔG > 0, the reaction is not spontaneous
– The reverse reaction is spontaneous
• If ΔG = 0, the reaction is at equilibrium
– Neither the forward nor the reverse reaction is favored
• ΔG is an extensive state function

75. Chemical
Thermodynamics
Ba(OH)2(s) + 2NH4Cl(s) → BaCl2(s) + 2NH3(g) + 2 H2O(l)
ΔH°rxn = 50.0 kJ (per mole Ba(OH)2)
ΔS°rxn = 328 J/K (per mole Ba(OH)2)
ΔG = ΔH - TΔS
ΔG°= 50.0 kJ – 298 K(0.328 kJ/K)
ΔG° = – 47.7 kJ Spontaneous
At what T does the reaction stop being spontaneous?
The T where ΔG = 0.
ΔG = 0 = 50.0 kJ – T(0.328 J/K)
50.0 kJ = T(0.328 J/K)
T = 152 K ←not spontaneous below 152 K

76. Chemical
Thermodynamics
Effect of ΔH and ΔS on
Spontaneity
ΔH
–
+
–
+
ΔS
+
+
–
–
Spontaneous?
Spontaneous at all temps
Spontaneous at high temps
• Reverse reaction spontaneous at low temps
Spontaneous at low temps
• Reverse reaction spontaneous at high temp
Not spontaneous at any temp
ΔG = ΔH – TΔS
ΔG negative ⇔ spontaneous reaction

77. Chemical
Thermodynamics
1. ΔG° = ΣΔG°f(products) - ΣΔG°f(reactants)
• ΔG°f = free energy change when forming 1 mole of
compound from elements in their standard states
2. ΔG° = ΔH° - TΔS°
3. ΔG° can be calculated by combining ΔG°
values for several reactions
• Just like with ΔH° and Hess’s Law
Ways to Calculate ΔG°rxn

78. Chemical
Thermodynamics
2H2(g) + O2(g) → 2 H2O(g)
1. ΔG° = ΣΔG°f(products) - ΣΔG°f(reactants)
ΔG°f(O2(g)) = 0
ΔG°f(H2(g)) = 0
ΔG°f(H2O(g)) = -229 kJ/mol
ΔG° = (2(-229 kJ) – 2(0) – 0) kJ = -458 kJ
2. ΔG° = ΔH° - TΔS°
ΔH° = -484 kJ
ΔS° = -89 J/K
ΔG° = -484 kJ – 298 K(-0.089 kJ/K) = -457 kJ

79. Chemical
Thermodynamics
2H2(g) + O2(g) → 2 H2O(g)
3. ΔG° = combination of ΔG° from other reactions
(like Hess’s Law)
2H2O(l) → 2H2(g) + O2(g) ΔG°1 = 475 kJ
H2O(l) → H2O(g) ΔG°2 = 8 kJ
ΔG° = - ΔG°1 + 2(ΔG°2)
ΔG° = -475 kJ + 16 kJ = -459 kJ
Method 1: -458 kJ
Method 2: -457 kJ
Method 3: -459 kJ

80. Chemical
Thermodynamics
What is Free Energy, Really?
• NOT just “another form of energy”
• Free Energy is the energy available to do useful work
• If ΔG is negative, the system can do work (wmax = ΔG)
• If ΔG is positive, then ΔG is the work required to
make the process happen
 Example: Photosynthesis
 6 CO2 + 6 H2O → C6H12O6 + 6 O2
 ΔG = 2870 kJ/mol of glucose at 25°C
 2870 kJ of work is required to photosynthesize 1 mole of
glucose

81. Chemical
Thermodynamics
Third Law of Thermodynamics
‫الحرارية‬ ‫للديناميكا‬ ‫الثالث‬ ‫القاتنون‬
The entropy of a pure crystalline substance at
absolute zero is 0.
‫المطلق‬ ‫الصفر‬ ‫حرارة‬ ‫درجة‬ ‫عند‬ ‫متبلورة‬ ‫نقية‬ ‫لمادة‬ ‫النتروبيا‬
.‫صفر‬
81Dr. Wael A. El-Helece

82. Chemical
Thermodynamics
The Third Law:
The entropy of a perfect crystal at
0 K is zero.
‫درجة‬ ‫عند‬ ‫مثالية‬ ‫بلورة‬ ‫فى‬ ‫العشوائية‬
.‫صفر‬ ‫المطلق‬ ‫الصفر‬
Everything in its place ‫مكانه‬ ‫فى‬ ‫شئ‬ ‫كل‬
No molecular motion ‫فى‬ ‫حركة‬ ‫توجد‬ ‫ل‬
‫الجزيئات‬
Third Law of Thermodynamics
‫الحرارية‬ ‫للديناميكا‬ ‫الثالث‬ ‫القاتنون‬