Energy Flashcards
(unit 3)
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 – SI system
Calories - English
Units of Energy
Chemical Potential Energy – stored in
chemical bonds
Heat – form of energy that flows between
objects at different temperatures.
Heat – form of energy associated with the
random motion of atoms & molecules. Hot
atoms move fast!
Energy in Chemistry
The potential energy a molecule
possesses by virtue of its structure
and composition.
Chemical Potential
Energy
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
1) They have different units!
2) Heat energy depends on how
much stuff! Temperature
does not.
Differences between heat &
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
…
In collisions!
How is Kinetic Energy
transferred between
particles?
a)
Graph a
b)
c)
d)
Which graph best shows
the relationship between
Kelvin temperature &
average KE?
Total energy is conserved.
Energy before = Energy after
Energy lost = Energy gained
Energy can be converted from 1 form to
another.
Energy can flow between the system and the
environment.
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 releases 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
Q = mCT
Quantity of heat transferred
depends on …
Amount of energy required to
raise the temperature of one
gram of a substance by 1C.
Different for every substance.
CH2O = 4.18 J/g (Table B)
Specific Heat
C (upper case) for NYS Regents
s (lower case) for almost
everyone else.
Symbol for specific heat
Equation used to calculate
energy change when a pure
substance in one phase is
heated or cooled.
Q = mCT
Calorimetry: the process of
measuring the heat absorbed or
released during a chemical or
physical change.
Relies on the Law of
Conservation of Energy
Coffee Cup calorimeter or
Constant Pressure Calorimeter
Calculating Heat Transferred
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
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 H2O is the environment.
• The NaOH in the water is the system.
Styrofoam Cup
Initial temperature
of water = 22C
Temperature = 30C
In a calorimetry exp’t, H2O is the
environment. The system is the stuff
in the water.
If the temperature of the H2O , the
process was ______________.
exothermic
Exothermic
In a calorimetry exp’t, H2O is the
environment. The system is the stuff
in the water.
If the temperature of the H2O , the
process was ______________.
endothermic
Endothermic
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
Going Up the ladder =
Endothermic Process
Net gain in energy.
Going Down the ladder =
Exothermic Process
Net loss in energy.
As a substance moves up the ladder,
the distance between its molecules
increases.
Solid
Molecules are ALWAYS attracted to
one another.
By looking at changes in
temperature!
How do we assess changes in
average kinetic energy?
By looking at changes in
phase!
How do we assess changes in
potential energy?
Equation
Name of phase change
Energy Change
H2O(s)  H2O(l)
Melting or fusion
Endothermic
H2O(s)  H2O(g)
Sublimation
Endothermic
Evaporation / Boiling
Endothermic
Freezing
Exothermic
Condensation
Exothermic
Deposition
Exothermic
H2O(l)  H2O(g)
H2O(l)  H2O(s)
H2O(g)  H2O(l)
H2O(g)  H2O(s)
Fill in the name and energy
change (endo or exo)
Melting Point
Freezing point
Solid-Liquid Equilibrium
Temperature
Boiling Point
Liquid-Gas Equilibrium
Temperature
Shows chemical information and
Heat Flow information
2NH4Cl(s) + Ba(OH)28H2O + heat 
2NH3(g) + BaCl2(s) + 10H2O(l)
Thermochemical Equation
Heat term is on the product
side
Exothermic Reaction
3H2(g) + N2(g)  2NH3(g) + Heat
or
3H2(g) + N2(g)  2NH3(g) + 91.8 kJ
Heat term is on the reactant
side.
Endothermic Reaction.
H2(g) + I2(g) + heat  2HI(g)
or
H2(g) + I2(g) + 53.0 kJ  2HI(g)
P.E.
Products
Reactants
The only way to get to
higher PE is to absorb
some energy from the
environment!
Endothermic!
In what kind of change do the products
have MORE potential energy than the
reactants?
P.E.
The only way to get to
lower PE is to release
some energy to the
environment!
Reactants
Products
Exothermic!
In what kind of change do the products
have LESS potential energy than the
reactants?
The Kelvin and
centigrade
degree are the
same size! They
both have 100
degrees between
the freezing
point of water
and the boiling
point of water.
How do the sizes of the centigrade
degree and the Kelvin compare?
50C + 273 = 323 K
85C + 273 = 358 K
358 K – 323 K = 35 K
Hey!
85C - 50C = 35C
When you take a difference, the number
is the SAME!
The temperature of a sample of a substance
changes from 50C to 85C. How many Kelvin
degrees does the temperature change?
Strong IMF!
What kind of intermolecular
forces do solids have?
Weak IMF!
What kind of intermolecular
forces do gases have?
I2 and CO2 (dry ice)
Name 2 substances that
sublimate.
Weak IMF. They sublimate easily.
What kind of intermolecular
forces do I2 and CO2 have?