Work force x distance The ability to do work Work cause a change or move an object Many types all can be changed into the other Energy Potential stored energy Position condition or composition ID: 779561
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Slide1
Energy
Energy is defined as the ability to do work.
Work = force x distance
Slide2The ability to do
work.
Work - cause a change or move an object.Many types- all can be changed into the other.
Energy
Slide3Potential
- stored energy
Position, condition or composition
Kinetic Energy-
energy something has because its movingHeat- the energy that moves because of a temperature difference.Chemical energy- energy released or absorbed in a chemical change.Electrical energy - energy of moving charges
Types of energy
Slide4Radiant Energy-
energy that can travel through empty space (light, UV, infrared, radio)
Nuclear Energy – Energy from changing the nucleus of atoms
*All types of energy can be converted into others.
If you trace the source far enough back, you will end up at nuclear energy.Types of Energy con’t
Slide5Energy can be neither created or destroyed in ordinary changes (not nuclear), it can only change form.
Discovered by Julius Robert Mayer in 1842
Now called: The First Law of Thermodynamics
Conservation of Energy
Law of Conservation of Mass - Energy The total amount of mass and energy in the universe is constant.
Slide6Some theories are based on supporting postulates.
A postulate is a statement which is agreed on by consensus among scientists.
The following are important postulates of the kinetic molecular theory:
The kinetic molecular theory is useful in describing thermal energy, heat, and temperature.
Slide7All matter consists of atoms.
Atoms may join together to form molecules.
Solids usually maintain both their shape and their volume.
Liquids maintain their volume, but not their shape.
Gases do not maintain shape or volume. They will expand to fill a container of any size. Molecular motion is random. Molecular motion is greatest in gases, less in liquids, and least in solids. Collisions between atoms and molecules transfers energy between them. Molecules in motion possess kinetic energy. Molecules in gases do not exert large forces on one another, unless they are colliding.Also see chapter 11 of textbook
Kinetic Molecular Theory
Slide8Thermal energy
is the average of the potential and kinetic energies possessed by atoms and molecules experiencing random motion. Heat is transferred by
convection
, conduction, or radiation. (review the definitions of these words)Heat is the thermal energy transferred from one object to another due to differences in temperature. Heat flow from high to low temperature.
Slide9There is no direct method used to measure heat. Indirect methods must be used.
Temperature
is a measure of the average kinetic energy of the molecules of a substance.
There is a direct relationship between temperature and avg. kinetic energy!
Temperature can be measured with a thermometer.
Slide10One way a thermometer can be calibrated is by the amount of
thermal expansion
and contraction that occurs within a given type of substance. Thermometers are limited by the physical properties of the substance from which they are made. (
i.e.
, An alcohol thermometer is of little use above the boiling point of alcohol, and a mercury thermometer will not be of any use below the freezing point of mercury.)
Slide11Both scales are based on the freezing conditions of water, a very common and available liquid. Since water freezes and boils at temperatures that are rather easy to generate (even before modern refrigeration), it is the most likely substance on which to base a temperature scale.
What's the difference between the Fahrenheit and Celsius temperature scales?
Slide12100ºC
212ºF
100ºC = 212ºF
0ºC = 32ºF
0ºC
32ºF
Slide13Zero Fahrenheit was the coldest temperature that the German-born scientist Gabriel Daniel Fahrenheit could create with a mixture of ice and ordinary salt.
He invented the mercury thermometer and introduced it and his scale in 1714 in Holland, where he lived most of his life.
Slide14Anders Celsius
, a Swedish astronomer, introduced his scale is 1742.
For it, he used the freezing point of water as zero and the boiling point as 100.
For a long time, the Celsius scale was called "centigrade."
The Greek prefix "centi" means one-hundredth and each degree Celsius is one-hundredth of the way between the temperatures of freezing and boiling for water. The Celsius temperature scale is part of the "metric system" of measurement (SI) and is used throughout the world, though not yet embraced by the American public.
Slide15100ºC
212ºF
0ºC
32ºF
100ºC = 212ºF
0ºC = 32ºF
100ºC = 180ºF
How much it changes
Slide16100ºC
212ºF
0ºC
32ºF
100ºC = 212ºF
0ºC = 32ºF
100ºC = 180ºF
1ºC = (180/100)ºF
1ºC = 9/5ºF
How much it changes
Slide17Scientists use a third scale, called the "absolute" or Kelvin scale.
This scale was invented by William Thomson, Lord Kelvin, a British scientist who made important discoveries about heat in the 1800's.
Scientists have determined that the coldest it can get (theoretically) is minus 273.15 degrees Celsius.
This temperature has never actually been reached, though scientists have come close. The value, minus 273.15 degrees Celsius, is called "absolute zero".
At this temperature scientists believe that molecular motion would stop. You can't get any colder than that. The Kelvin scale uses this number as zero. To get other temperatures in the Kelvin scale, you add 273 degrees to the Celsius temperature.
Slide18The important idea is that temperature is
really a measure
of somethin
g, the average
motion (kinetic energy,KE) of the molecules.KE = ½ mv2Does
0°C
really mean
0 K
E?
nop
e... it simply means the
freezing point of water, a
convenient
standard.
We have to cool things down to –273.15°C before we reach
0 KE. This is called 0 Kelvin (0 K, note: NO ° symbol.)
For phenomena that are proportional to the KE of the
particles (pressure of a gas, etc.) you must use
temperatures in K.
Slide19K = °C + 273
°C = K – 273
°F = 9/5 °C + 32
°C = 5/9 (°F – 32)
Temperature ConversionNote: In Kelvin notation, the degree sign is omitted: 283K
Slide20*A mental shortcut for a rough estimate:
· Double the temperature given in Celsius
· Add 30 to the result to find the approximate temperature in Fahrenheit.
Celsius to Fahrenheit:
Slide21Celsius Temperature to
Fahrenheit
More Celsius to
Fahrenheit
Fahrenheit to Celsius
More Fahrenheit to
Celsius
Slide22Fahrenheit to Celsius:
*A mental shortcut for a rough estimate:
·Subtract 30 from the temperature given in Fahrenheit
· Take half of the result to find the approximate temperature in Celsius.
Slide23Celsius Temperature to
Fahrenheit
More Celsius to
Fahrenheit
Fahrenheit to Celsius
More Fahrenheit to
Celsius
Slide24Energy is measured in many ways.
BTU
One of the basic measuring blocks is called a Btu. This stands for British thermal unit and was invented by the English.
Btu is the amount of heat energy it takes to raise the temperature of one pound of water by one degree Fahrenheit, at sea level.
One Btu equals about one blue-tip kitchen match. One thousand Btus roughly equals: One average candy bar or 4/5 of a peanut butter and jelly sandwich. It takes about 2,000 Btus to make a pot of coffee.
How Do We Measure Energy?
Slide25A
calorie
is a unit of measurement for energy. Calorie is a French word derived from the Latin word:
calor
(heat). Modern definitions for calorie fall into two classes:The small calorie or gram calorie approximates the energy needed to increase the temperature of 1 gram of water by 1 °C
. This is about 4.184
joules
.
The
large calorie
or
kilogram calorie
approximates the energy needed to increase the temperature of 1
kg
of water by 1 °C. This is about 4.184
kJ
, and exactly 1000 small calories.
1 cal = 4.184 J
Calorie
Slide26Energy also can be measured in joules. (Joules sounds exactly like the word jewels, as in diamonds and emeralds.)
A thousand joules is equal to a British thermal unit.
1,000 joules = 1 Btu
So, it would take 2 million joules to make a pot of coffee.
Joule
Slide27The term "joule" is named after an English scientist
James Prescott Joule
who lived from 1818 to 1889.
He discovered that heat is a type of energy.
One joule is the amount of energy needed to lift something weighing one pound to a height of nine inches. Around the world, scientists measure energy in j.
Slide28Like in the metric system, you can have kilojoules -- "kilo" means 1,000.
1,000 joules = 1
kilojoule = 1 Btu
1 cal = 4.184 J
Slide29Temperature is a measure of the Average
kinetic energy of the molecules of a substance.
Higher temperature faster molecules.At absolute zero (0 K) all molecular motion would stop.
Kinetic Energy and Temperature
Slide30Kinetic Energy
% of Molecules
High temp
.
Low temp.
Slide31Kinetic Energy
% of Molecules
High temp.
Low temp.
Average kinetic energies are temperatures
Slide32The average kinetic energy is
directly
proportional to the temperature in Kelvin If you double the temperature (in Kelvin) you double the average kinetic energy.
If you change the temperature from 300 K to 600 K the kinetic energy doubles.
Temperature
Slide33If you change the temperature from 300ºC to 600ºC the Kinetic energy doesn’t double.
873 K is not twice 573 K
Temperature
Slide34Phase Changes
Solid
Liquid
Gas
Melting
Vaporization
Condensation
Freezing
Slide35Liquid
Sublimation
Melting
Vaporization
Deposition
Condensation
Solid
Freezing
Gas
endothermic
exothermic
Slide36Water
Water
and Ice
Ice
Water and Steam
Steam
-20
0
20
40
60
80
100
120
0
40
120
220
760
800
Heating Curve for Water
Slide37Water
Water
and Ice
Ice
Water and Steam
Steam
-20
0
20
40
60
80
100
120
0
40
120
220
760
800
Heating Curve for Water
Slope = Specific Heat
gas
liquid
Solid
Slide38Water
Water
and Ice
Ice
Water and Steam
Steam
-20
0
20
40
60
80
100
120
0
40
120
220
760
800
Heating Curve for Water
Both Solid and liquid
Slide39Water
Water
and Ice
Ice
Water and Steam
Steam
-20
0
20
40
60
80
100
120
0
40
120
220
760
800
Heating Curve for Water
Both liquid and gas
Slide40Water
Water
and Ice
Ice
Water and Steam
Steam
-20
0
20
40
60
80
100
120
0
40
120
220
760
800
Heating Curve for Water
Heat of Vaporization
Slide41Water
Water
and Ice
Ice
Water and Steam
Steam
-20
0
20
40
60
80
100
120
0
40
120
220
760
800
Heating Curve for Water
Heat of Fusion
Slide42Water
Water
and Ice
Ice
Water and Steam
Steam
-20
0
20
40
60
80
100
120
0
40
120
220
760
800
Heating Curve for Water
Plateau = phase equilibrium
Slide4343
Energy and phase changes
Slide44J Deutsch 2003
44
Heat is transferred to different materials at different rates.
The specific heat capacity (C) determines the rate at which heat will be absorbed
.Even though mass is present in the formula it is an intensive property like density and is unique for each substance.The specific heat capacity for water is 4.18J/gThe quantity of heat absorbed (Q) can be calculated by: Q=mCT
m=mass
T=change in temperature
Slide45Heat Capacity
Heat capacity is an
extensive property
, meaning it
depends on the mass of the object. Ex: 1000g of water can hold more heat than 10 g of water.
Slide46Q means heat energy lost or gained.
Law of Conservation of Mass-Energy
m= mass of substance; Cp= specific heat capacity;
D
T = change in temperature Qlost = QgainedThree equations: Q= mass x Cp x DTQ= Hf x mass
Q= H
v
x mass
Calculating Energy
Slide47Water
Water
and Ice
Ice
Water and Steam
Steam
-20
0
20
40
60
80
100
120
0
40
120
220
760
800
Heating Curve for Water
Slide48Heat of fusion energy required to change one gram of a substance from solid to liquid. (endothermic
rxn
)Heat of solidification energy released when one gram of a substance changes from liquid to solid. (exothermic
rxn
)For water 80 cal/g or 334 J/gEnergy and Phase Change
Slide49Heat of vaporization energy required to change one gram of a substance from liquid to gas. (endothermic rxn)
Heat of condensation energy released when one gram of a substance changes from gas to liquid. (exothermic rxn)
For water 540 cal/g or 2260 J/g
Energy and Phase Change
Slide50Three equations:
Q= mass x C
p x DT (used at slopes)
Q= Hf x mass (used at s/l equilibria)Q= Hv x mass (used at l/g equilibria)
Slide51Water
Water
and Ice
Ice
Water and Steam
Steam
-20
0
20
40
60
80
100
120
0
40
120
220
760
800
Heating Curve for Water
Slide5252
Regents Question: 06/02 #28
As ice melts at standard pressure, its temperature remains at 0°C until it has completely melted. Its potential energy
(1) decreases
(2) increases
(3) remains the same
þ
Slide5353
Regents Question: 08/02 #54
A sample of water is heated from a liquid at 40°C to a gas at 110°C. The graph of the heating curve is shown in your answer booklet.
a
On the heating curve diagram provided in your answer bookle
t, label
each
of the following regions:
Liquid, only Gas, only Phase change
Liquid Only
Gas Only
Phase change
Slide5454
Regents Question: cont’d
b
For section
QR of the graph, state what is happening to the water molecules as heat is added.
c
For section
RS
of the graph, state what is happening to the water molecules as heat is added.
They move faster, their temperature increases.
Their intermolecular bonds are breaking, their potential energy is increasing.
Slide5555
Regents Question: 01/02 #47
What is the melting point of this substance?
(1) 30°C (3) 90°C
(2) 55°C (4) 120°C
þ
Slide5656
The quantity of energy absorbed or released during a phase change can be calculated using the Heat of Fusion or Heat of Vaporization
Melting (fusion) or freezing (solidification)
Q=
mHf where Hf is the heat of fusion (for water: 333.6 J/g)Boiling (vaporization) or condensing
Q=
mH
v
where
H
v
is the heat of vaporization
(for water: 2259 J/g)
H
f
and
Hv
are given to Table B – m is the mass
Slide57J Deutsch 2003
57
Regents Question: 08/02 #24
In which equation does the term “heat” represent heat of fusion?
(1) NaCl(s) + heat
NaCl(l)
(2) NaOH(aq) + HCl(aq)
NaCl(aq) + H
2
O(l)+ heat
(3) H
2
O(l)+ heat
H
2
O(g)
(4) H
2
O(l)+ HCl(g)
H
3
O
+
(aq) + Cl
–
(aq) + heat
Fusion refers to melting.
þ
Slide58J Deutsch 2003
58
Melting Point
The temperature at which a liquid and a solid are in equilibrium
The melting point for ice is 0ºCThe melting point of a substance is the same as its freezing point
Slide59J Deutsch 2003
59
Regents Question: 08/02 #18
The solid and liquid phases of water can exist in a state of equilibrium at 1 atmosphere of pressure and a temperature of
(1) 0°C (3) 273°C
(2) 100°C (4) 373°C
þ
Slide60The total heat = the sum of all the heats you have to use
Go in order
To calculate Q from ice
gas
HeatIceBelow 0
°
C
+
Melt Ice
At
0
°
C
+
Heat Water
0
°
C
-
100
°
C
+
Boil Water
At
100
°
C
+
Heat Steam
Above
100
°
C
Slide61Water
Water
and Ice
Ice
Water and Steam
Steam
-20
0
20
40
60
80
100
120
0
40
120
220
760
800
Heating Curve for Water
Q
Q
Q
Q
Q
+
+
+
+
Slide62Water
Water
and Ice
Ice
Water and Steam
Steam
-20
0
20
40
60
80
100
120
0
40
120
220
760
800
Heating Curve for Water
Q=m x Cp x ∆T
Q= H
f
x m
Q=m x Cp x ∆T
Q=m x Cp x ∆T
Q= H
v
x m