Download Energy and Phase Change Teacher

TEKS 11A: Understand energy and its forms, including kinetic, potential, chemical, and thermal
energies.
What is energy?
The capacity to do work or to produce
heat is called energy.
• Energy has neither mass nor volume.
• Energy is detected only because of its
effects.
TEKS 11A: Understand energy and its forms, including kinetic, potential, chemical, and thermal
energies.
Units of energy
• The SI unit of energy is the joule (J). A common
non-SI unit of energy is the calorie.
• One calorie (cal) is the quantity of heat that raises
the temperature of 1 g of pure water by 1ºC.
• Your STAAR formula chart has the conversion
factors you will use in class.
1. Calculate How many joules of energy are in a donut that
contains 200.0 Calories?
TEKS 11A: Understand energy and its forms, including kinetic, potential, chemical, and thermal
energies.
Kinetic energy
The energy an object has because of its motion is called kinetic
energy.
•The kinetic energy of any moving object depends on its
mass and speed.
1
kinetic energy =
mass × speed
2
1 2
KE = mv
2
•In chemistry, the kinetic energy is reflected in the motion of
the particles and the temperature of the system.
2
TEKS 11A: Understand energy and its forms, including kinetic, potential, chemical, and thermal
energies.
Potential energy
Energy that is stored as a result of position or shape is
called potential energy.
P E
In chemistry:
o n
Intermolecular
Forces
(IMFs)
Hydrogen Bonds in water molecules
t
e
n
t
i
a
l
e
r
g
y
Chemical
Bonds
O
H
H
TEKS 11A: Understand energy and its forms, including kinetic, potential, chemical, and thermal
energies.
Chemical energy
The Potential Energy stored in the chemical bonds of a
substance is called chemical energy.
•During a chemical reaction, a substance is transformed into
another substance with a different amount of chemical
energy.
•Breaking covalent bonds requires energy
•Forming covalent bonds releases energy
TEKS 11A: Understand energy and its forms, including kinetic, potential, chemical, and thermal
energies.
Heat or Thermal Energy
Heat, q, is energy that transfers because of a temperature
difference between objects.
• Heat flows spontaneously from a warmer object to a cooler
object until the temperature of both objects is the same.
• Adding or removing heat to/from an object produces a change
in the kinetic energy of its particles.
• This change in KE can produce a change in temperature,
or…
• This change in KE can be used to produce a phase change.
1. Describe An ice cube at 0ºC is dropped into a cup of water
at 45ºC. Describe what happens to the ice and water in terms
of heat flow.
TEKS 11A: Understand energy and its forms, including kinetic, potential, chemical, and thermal
energies.
Conservation of energy
The law of conservation of energy states that
energy is neither created nor destroyed.
• During any process, the energy of the Universe remains unchanged.
• If the energy of the system increases, the energy of the surroundings
must decrease by the same amount.
• If the energy of the system decreases, the energy of the surroundings
must increase by the same amount.
Surroundings
Universe
System
The
is
EVERYTHING together
TEKS 11A: Understand energy and its forms, including kinetic, potential, chemical, and thermal
energies.
Endothermic process
Heat is absorbed from the surroundings in
an endothermic process.
TEKS 11A: Understand energy and its forms, including kinetic, potential, chemical, and thermal
energies.
Exothermic process
An exothermic process is one that
releases heat to its surroundings.
TEKS 11A: Understand energy and its forms, including kinetic, potential, chemical, and thermal
energies.
TEKS 11A: Understand energy and its forms, including kinetic, potential, chemical, and thermal
energies.
A – Increase in
KE produces an
increase in
temperature
TEKS 11A: Understand energy and its forms, including kinetic, potential, chemical, and thermal
energies.
B – Increase in
KE overcomes
attraction
between
molecules.
T = constant
TEKS 11A: Understand energy and its forms, including kinetic, potential, chemical, and thermal
energies.
C – Increase in
KE produces an
increase in
temperature
TEKS 11A: Understand energy and its forms, including kinetic, potential, chemical, and thermal
energies.
D – Increase in
KE overcomes
attraction
between
molecules
T = constant
TEKS 11A: Understand energy and its forms, including kinetic, potential, chemical, and thermal
energies.
E – Increase in
KE produces an
increase in
temperature
TEKS 11A: Understand energy and its forms, including kinetic, potential, chemical, and thermal
energies.
E – Decrease in
KE produces a
decrease in
temperature
TEKS 11A: Understand energy and its forms, including kinetic, potential, chemical, and thermal
energies.
D – Decrease in
KE allows
molecules to
slow so attraction
can pull them
together. T = Const.
TEKS 11A: Understand energy and its forms, including kinetic, potential, chemical, and thermal
energies.
C – Decrease in
KE produces a
decrease in
temperature
TEKS 11A: Understand energy and its forms, including kinetic, potential, chemical, and thermal
energies.
B – Decrease in
KE allows
molecules to
slow so attraction
can pull them
together. T = Const.
TEKS 11A: Understand energy and its forms, including kinetic, potential, chemical, and thermal
energies.
A – Decrease in
KE produces a
decrease in
temperature