Transcript Energy - nnhschemistry

and
Chemistry?
Joules or calories
Joules or calories
Joules or calories
Joules or calories
Evidence of Energy
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Motion
Heat
Light
Sound
Energy Units
 joule ≡ energy exerted by a force of one Newton
acting to move an object through a distance of one
meter (SI unit)
 calorie ≡ the amount of energy required to heat 1
gram of water 1oC
 Calorie = 1000 calories
 1Joule = 0.2390 cal
How much is 1 Joule of energy?
 the energy required to lift a small apple one
meter straight up.
 the energy released as heat by a quiet
person, every hundredth of a second.
 the kinetic energy of an adult human moving
a distance of about 6 inches every second.
Types of Energy
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Chemical
Heat
Light
Sound
Electrical
Magnetic
Motion
Nuclear
Gravitational
Chemical
Thermal
Kinetic
Light
E
Acoustic
Nuclear
Electromagnetic
Energy Transformations
Gravitational
Chemical
Thermal
Kinetic
Light
E
Acoustic
Nuclear
Electromagnetic
Energy Transformation
Either or Energy
 Energy can be sorted into one of two
categories –
either
– kinetic (the “doing the work” phase)
or
– potential (the getting ready to do work or the
“stored” phase)
Energy examples
Potential
Kinetic
Mechanical Energy
Mechanical Energy
and
and
?
?
Forms of Kinetic Energy
Electrical – movement of electrons
Electromagnetic – moving electro magnetic waves
(light, x-rays, gamma rays, radio waves)
Thermal – vibrations and movements of particles in a substance
Mechanical – movement of objects
Sound – movement of particles as energy travels through a medium
Potential Energy
Chemical – energy stored in the bonds of molecules
Stored mechanical – energy stored in an object based on its position
relative to some reference state (i.e. a wound springs, a stretched rubber
band, a boulder perched on the edge of a cliff)
Nuclear – energy stored in nucleus of an atom
Gravitational – energy stored based on relative position of two objects
How much energy is stored in
glucose?
C6H12O6
1 gram of carbohydrate releases 4 Calories when burned
1 gram of fat releases 9 Calories when burned
Chemical Energy
 Energy is stored in the bonds between
atoms.
 When chemical reactions occur, bonds are
broken and formed.
 The amount of energy released / absorbed
during a chemical reaction can be measured
and calculated from the bond energies
Bond Energy
 Energy is absorbed by atoms when their
bonds break.
(+ΔH) ≡ heat of bond breaking
 Energy is released when bonds form
between atoms.
(-ΔH) ≡ heat of bond formation
Bond Energy - Analogy
Imagine stretching a rubber band until it
breaks. You must do work to stretch
the band because the tension in the
band opposes your efforts. You lose
energy; the band gains it. Something
similar happens when bonds break in a
chemical reaction.
The energy required to break the bonds
is absorbed from the surroundings.
Bond Energy
436 kJ is stored in H-H
436 kJ is released when H-H is broken
Bond
Energy
(kJ/mol)
H-H
436
C-H
413
N-H
393
The higher the bond energy, the more
work is required to break the bond, the
more stable it is
Bond Energy
Bond
Energy
(kJ/mol)
Bond
Energy
(kJ/mol)
H-H
436
N-N
160
C-H
413
N=O
631
N-H
393
N triple N
941
P-H
297
N-O
201
C-C
347
N-P
297
C-O
358
O-H
464
C-N
305
O-S
265
C - Cl
397
O - Cl
269
C=C
607
O-O
204
C=O
805
C-F
552
O=O
498
C-S
259
Bond Energy
 Energy is absorbed when bonds break.
 Energy is released when bonds form.
 Energy is absorbed or released when the
heat capacities of the products and
reactants differ.
Calculating Energy of a Reaction
H2 + Cl2  2HCl
Breaking H bond =
436 kJ/mol
Breaking Cl bond =
242 kJ/mol
H-Cl bond forming =
-431 kJ/mol
Reactions and Energy
If heat is generated during a reaction ≡ exothermic
If heat is absorbed during a reaction ≡ endothermic
Calculating Energy of a Reaction
H2 + Cl2  2HCl
Moles of Bonds
Broken
Energy absorbed Moles of Bonds
(kJ)
Formed
Energy released
(kJ)
1 H-H @ 431.2
kJ
436
854
1 Cl-Cl @
243
2 H-Cl @427 kJ
679
854
Heat of Reaction is 679 – 854 = -175kJ; energy is released during the
reaction
Endothermic or exothermic?
Chemical Reactions and Energy
Energy released
H2 + Cl2
Bonds are broken
HCl
Calculating chemical energy
N2 + O2  2NO
Breaking one N bond =
946 kJ/mol
Breaking one O bond =
498 kJ/mol
Forming 2 N-O bonds =
2 x 631 kJ/mol = 1262 kJ/mol
Net energy released =
(946 + 498) + 2(-631) = +182 kJ/mol
Endothermic or exothermic?
Chemical Reactions and Energy
Energy absorbed
N2 + O2
Bonds are broken
NO
Calculating chemical energy
2H2 + O2  2H2O
Endothermic or exothermic?
Calculating chemical energy
CH4 (g) + 2O2 (g)  CO2 (g) + 2H2O (l)
Endothermic or exothermic?
Food – the ultimate potential energy
C6H12O6 + O2  CO2 + H2O + energy
ATP + heat
Do I need
energy?
Where does
energy
come from?
What is
energy?
Where does the energy in food
come from?
sun
CO2 + H2O + energy  C6H12O6 + O2