Download Section 2.1

Friday, Sept. 20th: “A” Day
Monday, Sept. 23rd: “B” Day
Agenda
Ch 1 Tests
Start Ch. 2: Matter and Energy
Section 2.1: “Energy”
Energy, physical/chemical changes, evaporation,
exothermic/endothermic, law of conservation of energy
Homework:
Pg. 45: #1-13
Phase Change Diagram WS
Concept Review: “Energy”
**Quiz over section 2.1 next time!**
Ch 1 Tests
“The Science of Chemistry”
Class
2A
4A
1B
3B
Average Score
(out of 60)
Percentage
Ch 2: Matter and Energy
Sec. 2.1: “Energy”
Energy: the capacity to do work, such as
moving an object, forming a new compound,
or generating light.
Energy is always involved when there is a
change in matter.
Changes in Matter can be Physical or
Chemical
Physical change: a change of matter from one
form to another without a change in chemical
properties.
The chemical nature of the substance does not
change.
Examples:
Ice melting
Water boiling
Changes in Matter can be Physical or
Chemical
Chemical change: a change that occurs when
one or more substances change into entirely
new substances with different properties.
A chemical change occurs whenever a new
substance is made.
Example:
Reaction of hydrogen + oxygen to produce water
+
Every Change in Matter Involves a
Change in Energy
All physical AND chemical changes involve a
change in energy.
Sometimes, energy must be supplied for the
change in matter to occur.
Example:
for ice to melt, energy must be supplied so
that the particles have enough energy to
slide past one another
Every Change in Matter Involves a
Change in Energy
If more energy is added to the melted ice and
the boiling point is reached, the particles of
the liquid will leave the liquid’s surface
through evaporation.
Evaporation: the change of a substance from
a liquid to a gas.
Energy and Change
Sometimes, energy is released when a change
in matter occurs.
Examples:
Energy is released when a vapor
turns into a liquid (condensation)
Energy is released when a liquid turns into
a solid (freezing)
Energy is released when hydrogen and
oxygen combine to form water
Endothermic/Exothermic Processes
Endothermic: describes a process in which
heat is absorbed from the environment
Examples
Ice melting
Water boiling
Endothermic/Exothermic Processes
Exothermic: describes a process in which a
system releases heat into the environment
Examples
Water freezing
Water condensing into
liquid from vapor
Hydrogen + oxygen form
water
Conservation of Energy
Law of conservation of energy: the law that
states that energy cannot be created or
destroyed but can be changed from one form
to another.
During any chemical or physical change, the
total quantity of energy remains constant.
Energy is Often Transferred
To keep track of energy changes, chemists use
the terms system and surroundings.
System: all of the components that are being
studied at any given time
Surroundings: everything outside
of the system
Conservation of Energy in a Chemical
Reaction
An exothermic process involves a transfer of
energy from a system to its surroundings.
An endothermic process involves a transfer of
energy from the surroundings to the system.
The total energy of the systems and their
surroundings remains the same.
Conservation of Energy in a Chemical
Reaction
Does this chart represent an exothermic or
endothermic process?
Energy Can be Transferred in Different
Forms
The transfer of energy between a system and
its surroundings can involve different forms of
energy:
Chemical
Mechanical
Light
Heat
Electrical
Sound
Heat
Heat: the energy transferred between objects
that are at different temperatures; energy is
always transferred from higher-temperature
objects to lower-temperature objects until
thermal equilibrium is reached.
Kinetic energy: the energy of an
object that is due to the object’s
motion
Energy Can be Released or Absorbed
as Heat
Exothermic reaction
Energy is released as heat
Endothermic reaction
Energy is absorbed as heat
Heat is Different From Temperature
Temperature: a measure of how hot or cold
something is; specifically, a measurement of
the average kinetic energy of the particles in
an object.
Temperature is Expressed Using
Different Scales
The two temperature scales that are used in
chemistry are:
Celsius, ˚C
Kelvin, K
0˚C = freezing point of water
0 K = absolute zero, the temperature at which
the minimum average kinetic energies of
all particles occur
To find °C = T(K) - 273
To find K = t(˚C) + 273
Transfer of Heat May Not Affect
Temperature
Heating Curve for Water
Transfer of Heat May Not Affect
Temperature
Notice that the temperature only increases
when the substance is in the solid, liquid, or
vapor states.
The temperature does not increase when the
solid is changing to a liquid or when the liquid
is changing to a gas.
The energy that is added is used to change
state.
Specific Heat
Specific Heat: the quantity of energy, as heat,
that must be transferred to raise the
temperature of 1 g of a substance 1 K or 1˚C.
The SI unit for energy is the joule (J)
Specific heat is expressed in:
joules per gram kelvin
(J/g · K)
Specific Heat
Metals tend to have low specific heats, which
indicates that relatively little energy must be
transferred as heat to raise their
temperatures.
Water has an extremely high specific heat.
This is why a metal pot gets hot fast but the
water inside it takes a long time to warm up.
Specific Heat
This is also why Lake Michigan is always so
cold, even in August!
It takes a long time to
warm something, like water,
that has a high specific heat.
Homework
Section 2.1 review, pg. 45: #1-13
Phase Change Diagram worksheet
Homework: Concept Review: “Energy”
**Next time: Sec 2.1 Quiz**