Download state of matter - Mayfield City Schools

Heat and
Temperature
Let’s Review
- According to the kinetic theory of matter, all matter is
made up of tiny particles – called atoms or molecules.
- These particles are always moving, and it is this
movement that helps decide what state of matter exists
(solid, liquid, gas, plasma).
- The particles have potential and kinetic energy (kinetic as
they are moving, and potential as they are potentially
attracted or repulsed by each other).
- The TOTAL of all these forms of energy in a particular
substance is called its thermal energy
STATES OF MATTER
SOLIDS
•Particles of solids are
tightly packed, vibrating
about a fixed position.
•Solids have a definite
shape and a definite
volume.
Heat
STATES OF MATTER
LIQUID
 Particles of liquids are
tightly packed, but are
far enough apart to
slide over one
another.
 Liquids have an
indefinite shape and a
definite volume.
Heat
STATES OF MATTER
GAS
 Particles of gases
are very far apart
and move freely.
 Gases have an
indefinite shape
and an indefinite
volume.
Heat
A.Intermolecular Forces
1. the attractive forces between molecules
2. states of matter are determined by the
strength of these forces
(IMF increase from gasliquidsolid)
Temperature
- When you strike a nail with a
hammer, it becomes warm. Why?
When you put a flame to a liquid,
the liquid becomes warmer as its
molecules move faster. Why?
- In both the above examples, the molecules are made to
race back and forth faster. In other words, they gain kinetic
energy. In general, the warmer an object, the more kinetic
energy its atoms and molecules possess.
- Temperature, the degree of “hotness” or “coldness” of
an object, is proportional to the average (NOT total) kinetic
energy of the atoms or molecules making it up.
Measuring Temperature
Temperature - a quantity that measures the kinetic
energy per molecule due to random motion.
- The scale most often used
world-wide is the Celsius
thermometer, where a zero
(0) is assigned to the
temperature at which water
freezes, and 100 is assigned
to the temperature at which
water boils (at standard
atmospheric pressure).
Measuring Temperature
- In the U.S., the number 32 is traditionally assigned to
the temperature at which water freezes, and the number
212 is the temperature at which water boils. This
thermometer is called the Fahrenheit scale.
Upper Limits of Temperature
- In principle, there is no upper limit to
temperature
-As thermal motion increases, a solid object first melts
than vaporizes. As the temperature is further increased,
molecules dissociate into atoms, and atoms lose some of
their electrons, thereby creating a cloud of electrically
charged particles – called plasma.
- Plasmas exist in stars, where the temperature is many
millions of degrees Celsius.
Lower Limits of Temperature
- In contrast to high temperatures, there is a definite limit at
the opposite end of the scale, called absolute zero.
- Temperature is based upon
kinetic energy of molecules.
The colder something is, the
slower the molecules.
Eventually, the molecules
will slow down SO much,
they will essentially stop
moving (they will be out of
energy, and so they can’t get
any colder).
Measuring Temperature
Heat
-We know that temperature is the hot or cold nature of
something (based on the kinetic energy of its molecules), so
what is heat? Heat is the thermal energy transferred from
one thing to another due to a temperature difference.
- If you touch a hot stove,
thermal energy enters your hand
because the stove is warmer than
your hand. When you touch a
piece of ice, thermal energy
passes out of your hand and into
the colder ice.
Transfer of
Heat Energy
Cup gets cooler while
hand gets warmer
-The direction of energy
flow is ALWAYS from a
warmer thing to a
neighboring cooler thing.
Ice gets warmer
while hand gets
cooler
-Heat is the thermal energy
transferred from one thing to
another due to a temperature
difference.
-Heat is simply thermal
energy in transit.
Why do you feel
cold on a winter
day?
Heat
When outdoors on a winter
day, you feel chilly not
because something called
“cold” gets to you, but
because you lose body heat
(hot to cold)
That’s the purpose of your
coat – to slow the heat flow
from your body to the
surrounding air.
Cold is just reduced
thermal energy.
Heat Versus
Cold
st
1
Law of Thermodynamics
-What we’ve learned thus far about heat and thermal energy
is summed up in the laws of thermodynamics. The word
thermodynamics stems from Greek for “movement of heat.”
-When thermal energy transfers as heat, it does so without
net loss or gain. The energy lost from one place is gained by
the other. This conservation of energy, when specifically
applied to thermal systems, is known as the
First Law of Thermodynamics: Whenever heat flows into
or out of a system, the gain or loss of thermal energy equals
the amount of heat transferred. (You can’t get something from
nothing because energy and matter are always conserved).
nd
2
Law of Thermodynamics
-The Second Law of Thermodynamics restates what we’ve
learned about the direction of heat flow:
Heat never spontaneously flows from a lower-temperature
substance to a higher-temperature substance (You can’t break
even; you can’t return to the same energy state because
entropy always increases).
-When heat flow is spontaneous (without the
assistance of external work), the direction of
the flow is always from hot to cold. Heat can
be made to flow the other way only when
additional energy is added to the system (like
with heat pumps and air conditioners).
Heat Transfer: Conduction
- Conduction involves
the transfer of heat
through direct contact
- Heat conductors
conduct heat well,
insulators do not
Heat Transfer: Convection
- Takes place in liquids and gases as molecules move
in currents
- Heat rises and cold settles to the bottom
Heat Transfer: Radiation
-Heat is transferred through space
-Energy from the sun being transferred to the Earth