Transcript Energy Flashcards (units 2, 6, & 7)

Energy Flashcards
(units 2, 6, & 7)
The ability to do work
ENERGY
Energy of position.
Stored energy.
Potential Energy
Energy of motion
Depends on how heavy &
how fast
Kinetic Energy
Electromagnetic Energy
Radiant Energy
Joules
Units of Energy
Chemical Potential Energy – stored in
chemical bonds
Heat – form of energy that flows
between objects at different
temperatures.
Energy in Chemistry
Hot to Cold
Direction of heat flow
Symbol for heat energy
Q
A measure of the avg. kinetic
energy of the particles of a
system.
Temperature is NOT energy.
Temperature
Increases!
As the temperature , the
avg. kinetic energy …
Decreases!
As the temperature , the
avg. kinetic energy …
is constant!
When the temperature is
constant, the avg. kinetic energy
…
Total energy is conserved.
Energy before = Energy after
Energy lost = Energy gained
Energy can be converted from 1
form to another.
Law of Conservation of Energy
Energy of Universe is conserved
Universe
EnvironmentEnvironment
System
Energy
Energy can
move between
the system and
the
environment.
EXO - energy leaves system
(exits).
Temperature of
environment 
Environment
Temperature of
system 
System
Energy
System has a net loss in energy! H is –’ve.
System loses energy
(heat) to environment.
Exothermic Process
Endo - Energy enters system
(entrance)
Temperature of
environment .
Environment
System
Energy
Temperature of
system .
System has a net gain in energy! H is +’ve.
System absorbs energy
(heat) from environment
Endothermic Process
1. Temperature change
2. Mass of substance
3. Specific Heat of substance
Quantity of heat transferred
depends on …
Calculating Heat Transferred
Simple system: Pure substance in a
single phase. To calculate heat gained
or lost, use:
Q = mCT
Q = amount of heat transferred
m = mass of substance
C = specific heat capacity of the
substance (Table B).
T = temperature change = Tfinal – Tinitial
Equation used to calculate
energy change when a
substance in 1 phase is
heated or cooled.
Q = mCT
Q
m
C
T
Calculating energy changes in H2O
Dissolving
• When 10 g NaOH dissolves, the
temperature of the H2O increases.
Add 100 g H2O
Styrofoam Cup
Close together. Not
interacting with H2O.
Pulled apart & interacting
with H2O.
Calorimetry
• The NaOH is the system.
• The H2O is the environment.
Styrofoam Cup
Initial temperature
of water = 22C
Temperature = 30C
Q
100g
CH2O =
4.18J/g
8
Q = 3344 Joules
Calculating energy changes in H2O
In a calorimetry exp’t, H2O is the
environment.
If the temperature of the H2O , the
process was exothermic.
If the temperature of the H2O , the
process was endothermic.
Exothermic
If energy is high, stability is low.
If enrgy is low, stability is high.
Energy and Stability
Potential Energy of System
Energy Changes at Phase Changes
Gas
Liquid
Solid
Going Up the ladder =
Endothermic Process
Net gain in energy.
Going Down the ladder
= Exothermic Process
Net loss in energy.
Q = mHf
Use this equation to calculate
energy changes for phase
changes between ice & liquid
water at 0C.
Calculating Energy Change at
Phase Change
Q = mHv
Use this equation to calculate
energy changes for phase
changes between steam & liquid
water at 100C.
Calculating Energy Change at
Phase Change
Q
m Hf
or
Q
m Hv
Temperature
I
II
III
IV
Solid
Solid &
Liquid
Liquid
Liquid &
Gas
Boil pt.
K.E.
K.E.↔
K.E.
K.E.↔
K.E.
P.E.
P.E.↔
P.E.↔
Melt pt.
P.E.
P.E.↔
Time
V
Gas
Melting & Boiling Points
• Plateaus = Phase changes = Potential
energy changes.
• Notice that as long as 2 phases are
present, the temperature is
constant.
• Melting point, Boiling point.
To analyze a heating/cooling
curve:
• Does the curve go uphill or downhill?
• Label the phases present in each region.
• Describe what happens to the K.E. in
each region.
• Describe what happens to the P.E. in
each region.
• Locate the melting point and boiling
point.
What happens to the temperature
as heat is added at the boiling
point?
• Nothing, until only 1 phase is
present!
Constant!
The boiling point of a pure
substance is …
Constant!
The melting point of a pure
substance is …
3 equations for Q
• Q = mCT
• Q = mHf
• Q = mHv
• Have to figure out which one to use
for a given problem.
• Depends which section of heating
curve.
• Look for hints in the problem.
Amount of energy required to convert
1 gram of a pure substance from the
solid to the liquid phase at the
melting point.
Heat of Fusion
Hf
Amount of energy required to convert
1 gram of a pure substance from the
liquid to the gas phase at the boiling
point.
Heat of Vaporization
Hv
Q = mCT
• Temperature
changed
• Temperature
increased
• Temperature
decreased
• Initial / Start
temperature
• Final temperature
• Ending
temperature
• From ____ to
____
• Water
Q = mHf
•
•
•
•
•
Ice
Freezing
Melting
At 0C (for H2O)
At constant temperature
Q = mHv
•
•
•
•
•
Steam
Boiling
Condensation
At 100C (for H2O)
At constant temperature