Thermal Energy and Matter

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27 Οκτ 2013 (πριν από 3 χρόνια και 10 μήνες)

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Thermal Energy and Matter

Section 16.1

Hmmm…


Why aren’t machines 100% efficient?


Where does that energy go?


Why do most things generate heat?

How does heat flow? Quick lab


I will give you two different temperatures
of water. They have the same volume


Find their initial temperatures


Mix them together in the Styrofoam cup


KEEP THE LID ON!


After 2 minutes, take the final temperature

What is heat?


Heat

is the transfer of thermal energy from
one object to another


Heat flows spontaneously from hot objects
to cold objects

How is heat different from temperature?


Temperature

is a measure of how hot or
cold an object is compared to a reference
point


Temperatures is really the average kinetic
energy of particles in a substance

How does heat flow?


Via collisions!






As molecules collide, energy can be transferred
(high to low)


We’re looking at the AVERAGE amount of
energy

What was thermal energy again?


Total potential and kinetic energy of the
particles

of an object


Depends on…


Mass


Temperature


Phase (solid, liquid, gas, etc) or an object

Which has more thermal energy?



Coffee or chocolate milk?







Why?

Which has more thermal energy?


Glass or pitcher of lemonade?






Why?

Which has more thermal energy?


Frozen ice pop or melted ice pop?







Why?

Which has more thermal energy?


Cup of coffee or pitcher of lemonade?







Why?


What’s happening here?

Thermal Contraction and
Expansion


As the temp drops, the particles…




Thermal contraction!

Thermal Contraction and
Expansion


As the temp raises, the particles…




Thermal expansion

Specific Heat


Which part of this pan would you rather
touch? Why?

Specific heat


Specific heat

is the amount of heat
needed to raise one gram of a material 1
°

Celsius



So does the wood or the metal have a
lower specific heat?

Highest?






Q = heat (J)


m = mass (g)


c = specific heat (
J/g∙
°
C

)


Δ
T = change in temperature (
°
C)

Problem


An iron skillet has a mass of 500.0

grams.
The specific heat of iron is 0.449

J/g∙
°
C.
How much heat must be absorbed to raise
the skillet's temperature by 95.0
°
C?


How much heat is needed to raise the
temperature of 100.0

g of water by
85.0
°
C?


Problem


How much heat is absorbed by a 750
-
g
iron skillet when its temperature rises from
25
°
C to 125
°
C?


In setting up an aquarium, the heater
transfers 1200

kJ of heat to 75,000

g of
water. What is the increase in the water's
temperature? (
Hint:

Rearrange the specific
heat formula to solve for Δ
T
.)



To release a diamond from its setting, a
jeweler heats a 10.0
-
g silver ring by
adding 23.5

J of heat. How much does the
temperature of the silver increase?


What mass of water will change its
temperature by 3.0
°
C when 525

J of heat
is added to it?


How do we measure changes in heat?


A calorimeter?


A
calorimeter

is a device used to measure
changes in thermal energy


A

calorimeter

uses

the

principle

that

heat

flows

from

a

hotter

object

to

a

colder

object

until

both

reach

the

same

temperature
.


These devices are sealed to prevent heat
from escaping

How is it used?


Have a mass of water at a certain
temperature


Have an unknown item massed at a
different temperature


Drop it in the water


Find the change in temperature of water

Reviewing Concepts


In what direction does heat flow on its own?


How is the temperature of an object related to
the average kinetic energy of its particles?


Name two variables that affect thermal energy.


What causes thermal expansion of an object
when it is heated?


How do the temperature increases of different
materials depend on their specific heats?



What principle explains how a calorimeter is
used to measure the specific heat of a sample
material?

Heat and Thermodynamics

Section
16.2

Heat transfer


There are three different ways that thermal
energy (heat) can transfer from substance
to another


Conduction


Convection


Radiation

Conduction


Conduction

is the transfer of thermal
energy with no overall transfer of matter


Within one substance


Between substances in contact


EX: Newton’s cradle


Solids v. liquids v. gases

Which would you rather grab?

Thermal conductors v. Insulators


Thermal conductors

are materials that
conduct thermal
energy well


Metal


Tile



Thermal insulators

are materials that
conduct thermal
energy poorly


Air


Wood


Wool


Styrofoam

Convection


Convection

is the transfer of thermal
energy when particles of a fluid move from
one place to another


Liquid or gas



Convection current

happens when a fluid
circulates in a loop as it heats and cools.

Oceans, weather systems,
magma in earth’s interior…

…and food

Radiation


Radiation

is the transfer of energy by
waves moving through space


Does
not

need matter to transfer through



Hotter something is, faster it radiates

All together!


Thermodynamics


Whole branch of science


Thermodynamics

studies conversion
between thermal energy and other forms
of energy


Three supporting laws

First Law of Thermodynamics


The first law of thermodynamics states
that energy is conserved


Can’t create nor destroy


AKA law of conservation of energy


Second Law of Thermodynamics


The second law of thermodynamics
states that thermal energy can flow
from cold to hot
ONLY

if work is
done to the system


Natural flow pattern: warm objects to cold
objects


Heat engines and the second law


A
heat engine

is a device that converts
heat into work


Will never be 100% because…


Energy not converted into work?
Waste heat



Overall, disorder of universe is always
increasing

Third Law of Thermodynamics


The third law of thermodynamics states
that absolute zero can never be
reached


Molecules always moving somewhat…why
efficiency can never be zero


The average temperature of the universe today
is approximately 2.73 K


The current world record was set in 1999 at 100
picokelvins

(
pK
), or 0.0000000001K, by cooling
the nuclear spins in a piece of rhodium metal.


In February 2003, the Boomerang Nebula was
observed to have the lowest natural temperature
ever recorded (~1K)


Facts about Absolute zero

Reviewing Concepts


Why is conduction in gases slower than conduction
in liquids or solids?


Give three examples of convection currents that
occur in natural cycles


What happens to radiation from an object as its
temperature increases?


State the first law of thermodynamics


In your own words, what is the second law of
thermodynamics?


State the third law of thermodynamics