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TOPIC: ENERGY
All physical & chemical changes are
accompanied by change in energy
The chemistry of energy changes is
known as Thermochemistry!
Stability and Energy
• If energy is high, stability is low
• If energy is low, stability is high
Energy: Ability to do Work
The SI unit for an energy measurement
is called the Joule (J)
EXAMPLE: 1 Joule = amount of energy
required to lift a golf ball 1 meter
Law of Conservation of Energy
• Energy is neither created nor destroyed in
ordinary chemical or physical change, rather it
can be converted from one form to another
- potential to kinetic - radiant to electric
- electric to heat
- chemical to kinetic
- chemical to electrical
Energy before = Energy after
Energy
Non-mechanical – too
small to see
Mechanical – large
enough to see
Kinetic
Potential
Chemical
(Not a complete list!)
Heat
Light
Electrical
Nuclear
Kinetic Energy (KE) – energy of motion
• KE = ½ x Mass x Velocity2 = ½ mV2
• KE depends on how heavy and how fast
Kinetic Molecular Theory: the
atoms and molecules making up
substances are in constant motion
Potential Energy (PE): energy of position;
stored energy of matter
EXAMPLES
stapler
Rubberband
• When Potential energy is released from
matter it becomes kinetic energy
Energy in Chemistry
=
chemical energy
heat energy
Chemical Energy
• energy stored in bonds; it is released as
the result of a chemical reaction
Heat Energy
Heat: energy that is in the process of
flowing from warmer object to a
cooler object
Symbol for heat energy = Q or q
The amount of heat required to raise
the temp. of 1 gram of water 10C = a
calorie

Other Energy Units:
calorie, Calorie, BTU’s

1 calorie = 4.18 Joules

1 Calorie = 1000 calories = 1 kilocalorie

NOTE: When your body breaks down food,
these reactions give off heat – which is
measured in calories (That’s why your food
is labelled in calories)
energy (heat) is given off =
exothermic
EXO - energy leaves system (exits)
Temperature of
environment 
Environment
Temperature of
system 
System
Energy
energy (heat) is absorbed =
endothermic
Endo - Energy enters system (enter)
Temperature of
environment 
Environment
System
Energy
Temperature of
system 
Energy of Universe is conserved
Universe
EnvironmentEnvironment
System
Energy
Energy can
move between
the system
and the
environment
Calorimeter: an
insulated devise
used for
measuring the
amount of heat
absorbed or
released during a
chemical or
physical change
“universe” is contained in
Styrofoam cup
“environment” is water****
“system” is whatever put in
water
Energy lost = Energy gained
Difficult to monitor “system”
Easy to monitor “environment”
(water)
Energy lost/gained by
environment =
Energy gained/lost by system
The amount of heat
transferred depends on 3
things
Temperature change
Mass of substance
Specific Heat of substance
Specific Heat
• The amount of heat required
to raise the temp of any
given substance by 10C
• Symbol = c
• Specific heat = a physical
constant
•
unique for each pure substance
Found in
Table B
Calculating Heat Transferred
Simple system:
•pure substance in single phase
•calculate heat gained or lost using:
Q = mCT
Q = amount of heat transferred
m = mass of substance
C = specific heat capacity of the substance.
T = temperature change = Tfinal – Tinitial
Calorimetry
10 grams of NaOH is dissolved in 100 g of
water & the temperature of the water
increases from 22C to 30C
• was dissolving process endothermic or
exothermic
• how do you know?
Exothermic – temperature of environment ↑
Dissolving
• What’s happening when NaOH dissolves?
Add H2O
molecules close together,
not interacting
molecules pulled apart &
interacting with H2O
Calorimetry
– Calculate energy released by NaOH as it
dissolves in water
Energy lost by NaOH = Energy gained by water
Easier to calculate from H2O perspective
Q = mCT
Q = energy (joules)
M = mass (grams)
C = specific heat capacity (Table B)
T = temperature change = Tf - Ti
Calorimetry & Q = mCT
temperature of water increased from 22C to
30C
 30C -22C = 8C = T
What mass to use? Well, temp change was for
water, so want mass of water
m = 100 g
Same goes for specific heat capacity; calculate
heat absorbed by water
cH 0 = 4.18J/g
2
Q = mCT
• Q = (100 g)(4.18 J/g)(8C)
• Q = 3344 Joules