Class №2 The theme: «Bioenergetics of chemical reactions».
1. Questions:
1. Subject and problems of thermodynamics.
2. Basic concepts: system, types of the systems (open, closed, isolated), state function.
3. Internal energy. The First law of thermodynamics.
4. Enthalpy. Exothermic and endothermic processes. Hess’s law.
5. Entropy. The Second and the Third laws of thermodynamics.
6. Gibbs energy (free energy). Spontaneous and nonspontaneous reactions.
2. Familiarize with teaching tasks:
№
Content of the task:
1. Determine the enthalpy (ΔН) of urea hydrolysis reaction if:
ΔН°f (CO(NH2 )2 ) = -319 кJ/mol
ΔН°f (Н2 О) = -285.8 кJ/mol
ΔН°f (СО2 ) = -413.6 кJ/mol
ΔН°f (NH3 ) = - 79.9 кJ/mol
СО(NH2)2 (s) + Н2О (l) → СО2 (g) + 2 NH3 (l)
Solution:
ΔH = ∑ ΔHfo (products) - ∑ ΔHfo (reactants)
ΔН = [ ΔН f °( С О 2 ) + 2  ΔН f °( N H 3 ) ] - [ ΔН f °( СО(NH2 )2) + ΔНf°(Н2 О)]
ΔН = [ - 413. 6 + 2  ( - 79. 9) ] - [ - 319. 2 + ( - 285. 8) ] = 31. 6 кJ
Reaction is endothermic.
2. Determine the entropy (ΔS) of reaction:
СН4(g) + 2О2(g) → СО2 (g) + 2Н2О (l).
S° (CH 4 ) = 186.3 J/(molK)
S° (O2 ) = 205 J/(molK)
S° (СО2) = 213.7 J/(molK)
S° (H2 O) = 70 J/(molK)
Solution:
ΔS = ∑ So (products) - ∑ So (reactants)
ΔS = [2 So (Н2O)(l) + So (СO2 )(g)] - [So (СН4)(g) + 2 So (О2)(g)]
ΔS = 2  70 + 213.7 – 186.3 - 2 205 = -242.4 J К -1.
С6Н12О6 → 2 СзН6Оз
3.
Is the spontaneous flowing of reaction possible?
ΔGfo (СзН6Оз ) = -539 kJ/mol
ΔGfo (С6Н12О6 ) = -917 kJ/mol
Solution:
ΔG = ∑ ΔGfo (products) - ∑ ΔGfo (reactants)
ΔG = 2ΔGfo (СзН6Оз ) - ΔGfo (С6Н12О6 )
ΔG = 2 (-539) – (-917) = -161 кJ
ΔG < 0 – reaction is spontaneous.
4.
Determine the standard Gibbs energy (ΔG) of reaction:
C 12 H 12 O 2 (s) + 11О 2 (g) → 12СО 2 (g) + 11Н2 О (l)
if ∆Н = -5650.69 кJ, ∆S = 2976.02 J/К
Solution:
∆G = ∆Н - T∆S
T = 25 + 273 = 298 K
∆S = 2976.02 J K -1 = 2.98 kJ K -1
∆G = ∆Н - T∆S = -5650.69 - 2982.98 = -5650.69 – 888.04 = -6538.73 kJ
3. Answer the multiple-choice test questions (in written form):
1
What is the thermodynamic standard state?
A t = 37oC, p =110 кPа, 1mol
B T = 298oK, p = 101.3 кPа, 1mol
C T = 273oK, p = 101.3 кPа, 0.1 mol
D t = 0oC, p = 760 mmHg, 1mmol
2
A
B
C
D
What is the mathematical expression of the First law of thermodynamics?
ΔG = ΔH - TΔS
P = iCRT
Q = ΔU + W
ΔS = ΔQ / T
A
B
C
D
Name the process occurs at the constant volume:
Isobaric
Exothermic
Isochoric
Endothermic
A
B
C
D
What is the mathematical expression of the Hess’s law?
ΔН = ΔG + ТΔS
Δ Н = ∑ΔНf (products) – ∑ΔНf (reactants)
ΔН = ΔH1 + ΔН2 + ΔН3
ΔН = ΔG-ТΔS
A
B
C
D
What thermodynamic function is symbolized with H?
Entropy
Enthalpy
Gibb’s energy
Internal energy
A
B
C
D
What is enthalpy change of an exothermic reaction?
ΔН > 0
ΔS < 0
ΔН < 0
ΔG > 0
A
B
C
D
What reaction enthalpy change is associated with standard enthalpy of formation of
nitrogen (II) oxide - ΔНоf(NO)?
½N2 + О → NО
N + ½О 2 → NО
½N2 + ½О2 → NО
2NН3 + 5/2О2 → 2 NO + 3Н2О
A
B
C
D
Thermodynamic function Entropy is a measure of:
Conductivity
Disorder
Spontaneity
Heat effect
3
4
5
6
7
8
9
The entropy of the perfectly crystalline substance at 0 K is equal to:
A 
B +1
C -1
D 0
10
A
B
C
D
What is the mathematical expression of the Second law of thermodynamics?
P = CRT
N = kP
Q = ΔU – A
ΔG = ΔH – TΔS
A
B
C
D
What is the value of Gibbs energy of spontaneous reaction?
∆G = 0
∆S<0
∆G < 0
∆G > 0
11
4. Tasks for an independent work (in written form):
1. Calculate ΔH for the process: 2Hg (l) + Cl2 (g)  Hg2Cl2 (s) if:
Hg (l) + Cl2 (g)  HgCl2 (s) ΔH1 = -224 kJ
Hg (l) + HgCl2 (s)  Hg2Cl2 (s) ΔH2 = -41.2 kJ
2. Calculate ΔHo for the chemical reaction: 2Na(s) + 2H2O(l)  2NaOH(aq) + H2 (g), using thermodynamic data from Appendix (ΔHfo(NaOH(aq)) = - 470 kJ/mol).
3. Calculate ΔS for the chemical reaction C2H4 (g) + O3 (g)  CH3CHO (g) + O2 (g), using thermodynamic data from Appendix (S°(CH3CHO (g)) = 250 J/(mol. K)).
4. Calculate ΔG for the chemical reaction: C12H22O11 (s) + 12O2 (g)  12CO2 (g) + 11H2O (l),
using thermodynamic data from Appendix.
5. Calculate ΔG for the following chemical reaction: CO (g) + 2H2 (g)  CH3OH(l), if
ΔH = -129 kJ/mol; ΔS = -333 J/mol. K-1. Predict if this reaction is spontaneous under the standard
conditions.
5. Topics of reports for training-research work of students (TRWS).
1. Chemical thermodynamics is theoretical basis of study of matter and energy exchange in a living
organism.
2. Features of living organisms as objects for thermodynamics researches.
Thermodynamic data for selected organic compounds at 298 К
Name
Methane
Ethyne
Ethene
Ethane
Benzene
Methanol
Ethanol
Glycerin
Formaldehyde
Acetic acid
Carbamide (urea)
Glucose
Sucrose
Lactose
Maltose
Substance
СH4 (g)
C2H2 (g)
C2H4 (g)
C2H6 (g)
C6H6 (aq)
CH3OH (l)
C2H5OH (l)
C3H8O3 (l)
СН2О (g)
CH3COOH (l)
CO(NH2)2 (s)
СО(NH2)2 (aq)
C6H12O6 (s)
C6H12O6 (aq)
C12H22O11 (s)
C12H22O11 (aq)
C12H22O11 (aq)
C12H22O11 (aq)
ΔHοf, кJ/mol
-74.9
226.8
52.3
-89.7
49.0
-238.7
-277.6
-669.1
-115.9
-484.4
-333.0
-317.7
-1273.0
-1263.1
-2220.9
-2215.8
-2232.4
-2238.3
Sο, J/(mol·К)
186.2
200.8
219.4
229.5
124.5
126.8
160.7
204.6
218.8
159.9
104.7
175.7
212.1
264.0
360.2
403.8
394.1
400.3
ΔGοf, кJ/mol
-50.8
209.2
68.1
-32.9
172.8
-166.3
-174.8
-479.4
-109.94
-389.6
-196.9
-202.7
-910.5
-914.5
-1544.3
-1551.4
-1564.9
-1573.6
Thermodynamic data for selected elements and compounds at 298 К
Substance
ΔHοf кJ/mol
Sο J/(mol·К)
ΔGοf
Al (s)
Al2O3 (s)
C (graphite)
ССl4 (l)
СО (g)
СО2 (g)
СаСО3 (s)
СaF2 (s)
Ca3N2 (s)
CaO (s)
Са(ОН)2 (s)
Сl2 (g)
Сl2O (g)
СlO2 (g)
Сl2O7 (l)
Сr2O3 (s)
СuO (s)
Fe (s)
FeO (s)
Fe2O3 (s)
Fe3O4 (s)
H2 (g)
HBr (g)
HCN (g)
HCl (g)
HF (g)
HI (g)
H2O (g)
H2O (l)
H2S (g)
KCl (s)
KClO3 (s)
MgCl2 (s)
Mg3N2 (s)
MgO (s)
N2 (g)
NH3 (g)
NH4NO2 (s)
NH4NO3 (s)
N2O (g)
NO (g)
N2O3 (g)
NO2 (g)
N2O4 (g)
N2O5 (g)
NiO (s)
O3 (g)
O2 (g)
P2O5 (s)
PbO (s)
PbO2 (s)
S (s)
SO2 (g)
SO3 (g)
SiH4 (g)
SiO2 (s)
SnO2 (s)
ZnO (s)
0
-1676.0
0
-135.4
-110.5
-393.5
-1207.0
-1214.6
-431.8
-635.5
-986.6
0
76.6
105.0
251.0
-1440.6
-162.0
0
-264.8
-822.2
-1117.1
0
-36.3
135.0
-92.3
-270.7
26.6
-241.8
-285.8
-21.0
-435.9
-391.2
-641.1
-461.1
-601.8
0
-46.2
-256.0
-365.4
82.0
90.3
83.3
33.5
9.6
-42.7
-239.7
142.3
0
-1492.0
-219.3
-276.6
0
-296.9
-395.8
34.7
-910.9
-580.8
-350.6
28.3
50.9
5.7
214.4
197.5
213.7
88.7
68.9
105.0
39.7
76.1
222.9
266.2
257.0
81.2
42.6
27.2
60.8
87.4
146.2
130.5
198.6
113.1
186.8
178.7
206.5
188.7
70.1
205.7
82.6
143.0
89.9
87.9
26.9
191.5
192.6
151.0
219.9
210.6
307.0
240.2
303.8
178.0
38.0
237.7
205.0
114.5
66.1
74.9
31.9
248.1
256.7
204.6
41.8
52.3
43.6
кJ/mol
0
-1582.0
0
-64.6
-137.1
-394.4
-1127.7
-1161.9
-368.6
-604.2
-896.8
0
94.2
122.3
-1050.0
-129.9
0
-244.3
-740.3
-1014.2
0
-53.3
125.5
-95.2
-272.8
1.8
-228.6
-237.3
-33.8
-408.0
-289.9
-591.6
-400.9
-569.6
0
-16.7
-183.8
104.1
86.6
140.5
51.5
98.4
114.1
-211.6
163.4
0
-1348.8
-189.1
-218.3
0
-300.2
-371.2
57.2
-856.7
-519.3
-320.7