Use the bond energies from the table in the reference sheet to determine the approximate enthalpy change of the following reaction. H2(g) + Br2(g) --> 2HBr(g)
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
Use the bond energies from the table in the reference sheet to determine the approximate enthalpy change of the following reaction.
H2(g) + Br2(g) --> 2HBr(g)
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Exam 3 Reference.pdf
Na
Mg
12
AI
Si
CI
09
15
18
21
2.5
3.0
K
Ca
Sc
TI
V
Cr
Mn
Fe
Co
Ni
Cu
19
Zn
16
Ga
Ge
Se
Br
08
10
13
15
16
16
15
19
19
16
18
20
24
28
Rb
To
Pd
22
Ag
19
Te
Sr
Y
Zr
Nb
Мо
Cd
In
Sn
Sb
OB
10
12
14
1.6
1.8
19
17
17
18
21
25
Ba La-Lu Hf
1.0-12
Cs
Та
1.5
Re
Os
Ir
Pt
Au
24
TI
Pb
Bi
Hg
19
Po
20
At
22
0.7
0.9
13
1.7
19
22
22
22
18
19
19
Np-No
14-13
Fr
Ra
Ac
Th
Pa
0.7
09
11
13
14
1.4
Electronegativity
difference between
bonding atoms
Bond type
Zero
Pure covalent
Covalent
Bond Type Electronegativity Difference
character
decreases;
ionic character
increases.
Intermediate
Polar covalent
pure covalent
< 0.4
polar covalent
between 0.4 and 1.8
Large
lonic
ionic
> 1.8
Formal Charge = # valence e - nonbonding e - ½ bonding e
ΔΗΣΣ(ΔΗ(bonds broken)) + Σ (ΔΗ(bonds formed)
Bond
Bond Energy (kJ/mol)
С-Н
415
O-H
464
Н-Н
436
С-О
350
C=0
1080
Br-Br
190
Н-Br
370
Li,
Bez
B2
C2
N2
O2
F2
Nez
opx
O2px
T2py: 2pz
O2px
O25
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