energy & bonding
DESCRIPTION
A set of slides created to teach Energy & Bonding to learners at Bishops Diocesan College in Cape Town.TRANSCRIPT
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Bonding & Energy
K Warne
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Bonding
O
H2O
O
H2O
OO
Two hydrogen molecules and one oxygen molecule react to form two water
molecules.
Two H-H
single bonds
One O=O
double bond
Four H-O
single bonds
BONDS BROKEN
2x H-H single bonds
1x O=O double bond
BONDS FORMED
4x O-H single bonds
2 H2 + O2 2 H2O
+
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e-
Bonding Theory
Why do atoms join together?
e- e-
?
e-
The nucleus of one atom attracts the electrons from the other atom.
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Bonding Theory
e- e-
e- e-
• Atoms are attracted to each other as the protons from one atom attract the electrons from another atom.
• As two atoms approach each other the energy of the system drops.
• When the atoms get close enough for the nuclei to begin repelling the energy begins to increase.
• If the atoms were forced closer the energy of the system would rise sharply.
e-e-
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H-H bond length pm (x10-12 m)
0
-100-
-200-
-300-
-400-
-432-
-500-
Bond Energy & Length1. Atoms are attracted
to each other as the protons from one atom attract the electrons from another atom.
2. As two atoms approach each other the energy of the system drops.
3. When the atoms get close enough for the nuclei to begin repelling the energy begins to increase.
4. If the atoms were forced closer the energy of the system would rise sharply.
The bond is stable when
the minimum energy
system is reached.
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Bond Enthalpies
+
Whenever a bond is formed ENERGY ____________.
Whenever a bond is BROKEN ENERGY is _________.Bond FORMING – _______________.
Bond BREAKING – ________________.
Bond Energy: The energy __________ to break a bond. (kJ.mol-1)
Stronger bonds _______________ bond energy.
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Exothermic Reactions
Reaction gives off energy to the surroundings – surroundings get HOT!
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Exothermic Reactions
Reaction ________________ the surroundings – _____________________!
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Exothermic ReactionsReaction gives off energy to the surroundings – surroundings get HOT!
540 kJ
Energy
140 kJ
Energy released
= 140 – 540 = -400 kJ
Energy of REACTION = ENERGY OF PRODUCTS– ENERGY OF REACTANTS
ΔHr = ΔHP - ΔHR
ΔHr for EXOTHERMIC is ALWAYS NEGATIVE!
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Exothermic ReactionsReaction gives off energy to the surroundings – surroundings get HOT!
Energy
needed to
...................
all bonds.
Energy
released
when
...............
bonds
...................
ΔHreaction = E............................ – E.................................
ΔHreaction ....... 0 (i.e. ...................)
ΔHreaction
H = internal
Heat Energy
or
ENTHALPY
E = ................
ENERGY
ΔHr= Ebreaking – E forming = ........– ........= ......... kJ
10
0 k
J
64
0 k
J
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(a) Energy
needed to
................ all
bonds.
Endothermic ReactionsReaction takes energy from the surroundings – surroundings get cold!
Reactants
Products
Activated Complex
(b) Energy released
when
..................................
(c)
(a)
(b)
ΔHreaction = Eproducts– Ereactants
= .........– .........= .......kJ
ΔHreaction .... 0 (i.e. ...............)
ΔHreaction
140kJ
540kJ
ΔHreaction = Ebreaking– Eforming
= ......– ........= ..........kJ
ΔHreaction ...... 0 (i.e. ...............)
60
0 k
JActivation energy
20
0 k
J
40
0
kJ
Or
ΔHr ....... 0
Overall ...........
energy taken in
than given out!
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Bond Length (pm) Energy
(kJ/mol)Bond Length (pm)
Energy
(kJ/mol)
H--H 74 436 H-C 109 413
C-C 154 348 H-N 101 391
N-N 145 170 H-O 96 463
O-O 148 145 H-F 92 568
F-F 142 158 H-Cl 127 432
Cl-Cl 199 243 H-Br 141 366
Br-Br 228 193 H-I 161 298
I-I 267 151 C-C 154 348
C-C 154 348 C=C 134 614
C-N 147 308 CC 120 839
C-O 143 360 O-O 148 145
C-S 182 272 O=O 121 498
C-F 135 488 N-N 145 170
C-Cl 177 330 C=O 120 799
C-Br 194 288
Can you identify any TRENDS or PATTERNS in this data?
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Bond Energy & Length
Bond FORMING – EXOTHERMIC.
Bond BREAKING – ENDOTHERMIC.
Bond Energy: E (kJmol-1)
• The amount of energy ____________
______________________________
• Given out when a bond is _________.
• Taken in when bond is ___________.
Po
ten
tia
l E
ne
rgy
Distance between nuclei
Bond Length: d (nm)
• The distance between ___________
_____________________________.
• _________ when bonds STRONGER.
• ___________ when bonds WEAKER.
e- e-
e- e-
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Energy Changes During Reactions
ΔHr = Hprod – HReact = Ebreaking– Eforming
Po
ten
tial E
nerg
y
Po
ten
tial E
nerg
y
H prod
HreactH prod
H react
You can determine ΔHr in TWO different ways. The equation you
use depends on the information you are given.
ΔHr > 0 ΔHr < 0
HbreakingHforming
HbreakingHforming
Given ENTHALPYS given BOND ENERGIES
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Bond Energy Calculations
H2 + Cl2 2H-Cl
H H
Cl Cl
H H
Cl Cl
H H
Cl Cl
Activated complexBonds Breaking/Forming
ΔHreaction = Ebreaking– Eforming
=
= …… – ……. = …….kJ
ΔHreaction > …… (i.e. ………….)
Look up the required bond energies:
E (H-H) =
E (Cl-Cl) =
E (H-Cl) =
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Bond Energy Examples
Use data from the bond energy table to
calculate the enthalpy of reaction for the
following reactions: (per mol of the first element in each
reaction)
1. O2 + 2 H2 2H2O (no 4 TT)
2. CH4 + O2 CO2 + H2O
3. CH3CH2OH + O2 CO2 + H2O
OC C
H
H
H
H
H
H
C
H
H
H
H
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Calculate Hr
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Born Haber Cycle
A large amount of energy (lattice) is released when the gaseous ions bond together into the ionic crystal lattice.
Ionic compounds are therefore very stable and require large amounts of energy to break the bonding.
Ionic compounds have HIGH MELTING POINTS we say they are thermally stable.
Na(s) + 1/2 Cl2(g) NaCl(s)
Na(g) + 1/2 Cl2(g)
Na(g) + Cl(g)
Na+(g) + e- + Cl(g)
Na+(g) + Cl
-
(g)Ionisation Energy
Dissociation Energy
Sublimation Energy
Electron
Affinity
Lattice Energy
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Hi -
This is a SAMPLE presentation only.
My FULL presentations, which contain a lot more more slides and other resources, are freely
available on my resource sharing website:
www.warnescience.net(click on link or logo)
Have a look and enjoy!
WarneScience