Transcript Properties of Matter - Broadneck High School

Temperature
Temperature Scales
Boiling point
of water
Fahrenheit
Celcius
Kelvin
212 oF
100 oC
373 K
180 oF
Freezing point
of water
32 oF
100 oC
0 oC
100 K
273 K
Notice that 1 kelvin degree = 1 degree Celcius
Temperature Scales
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 136
Temperature Scales
• Temperature can be subjective and so fixed scales had to be
introduced.
• The boiling point and freezing point of water are two such points.
• Celsius scale (oC)
– The Celsius scale divides the range from freezing to boiling into 100
divisions.
– Original scale had freezing as 100 and boiling as 0.
– Today freezing is 0 oC and boiling is 100 oC.
• Fahrenheit scale (oF)
• Mercury and alcohol thermometers rely on thermal expansion
Temperature is Average Kinetic Energy
*Vector = gives direction and magnitude
“HOT”
Fast
“COLD”
Slow
Kinetic Energy (KE) = ½ m v 2
Total kinetic energy is what we call heat.
Heat is measured with an instrument called a
calorimeter.
Temperature is measured with an instrument called a
thermometer.
Heat versus Temperature
lower temperature
Fractions of particles
higher temperature
TOTAL
= Heat
Kinetic ENERGY
Kinetic energy
Molecular Velocities
molecules sorted by speed
Fractions of particles
many different molecular speeds
the Maxwell speed distribution
speed
http://antoine.frostburg.edu/chem/senese/101/gases/slides/sld016.htm
Hot vs. Cold Tea
Many molecules have an
intermediate kinetic energy
Low temperature
(iced tea)
High temperature
(hot tea)
Percent of molecules
Few molecules have a
very high kinetic energy
Kinetic energy
Equal Masses of Hot and Cold Water
Thin metal wall
Insulated box
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 291
Water Molecules in Hot and Cold Water
Hot water
90 oC
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 291
Cold Water
10 oC
Water Molecules in the same
temperature water
Water
(50 oC)
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 291
Water
(50 oC)
Temperature vs. Heat
Different
Alike
Measured
with a
Thermometer
Have
Kinetic
Energy
Topic
Average
Kinetic
Energy
oCelcius
(or Kelvin)
Temperature
Different
Measured
with a
Calorimeter
Topic
A Property
of
Matter
Heat
Total
Kinetic
Energy
Joules
(calories)
Energy
(a) Radiant energy
(c) Chemical energy
(b) Thermal energy
(d) Nuclear energy
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.
(e) Electrical energy
Potential energy
Energy in
kinetic energy
Energy out
kinetic energy
The energy something possesses due to its motion, depending on mass and velocity.
Energy
A
is the ability to do work or
produce heat
C
B
Kinetic Energy – energy of motion
KE = ½ m v 2
mass
velocity (speed)
Potential Energy – stored energy
Batteries (chemical potential energy)
Spring in a watch (mechanical potential energy)
Water trapped above a dam (gravitational potential energy)
School Bus or Bullet?
Which has more kinetic energy;
a slow moving school bus or a fast moving bullet?
Recall: KE = ½ m v 2
BUS
KE = ½ m v 2
KE(bus) = ½ (10,000 lbs) (0.5 mph)2
BULLET
KE = ½ m v 2
KE(bullet) = ½ (0.002 lbs) (240 mph)2
Either may have more KE, it depends on the mass of the bus and the velocity
of the bullet.
Which is a more important factor: mass or velocity? Why?
(Velocity)2
Energy
Kinetic Energy
Potential Energy
energy due to the composition or
energy of motion
position of an object. (Chemical
Potential Energy – energy
Work – weight lifted
stored in a substance because of
through a height
its composition.
The potential energy results from
the arrangement of the atoms
Heat – symbol is q;
and the strength of the bonds that
nergy in the process join them. Stored energy is
f flowing from a warm released when bonds are
bject to a cooler one broken.)
Units of energy are the same, regardless of the form of energy
Units of energy
Most common units of energy
metric
calorie where 1 calorie (cal)
is the amount of energy
needed to raise the
temperature of 1 g of water
by 1°C.
kilocalorie
called a Calorie with a capital “C”
sometimes called nutritional
calories
1 Calorie = 1000 calories
SI
joule (J), defined as
1(kilogram•meter2)/second2,
energy is also expressed in
kilojoules (1 kJ = 103J).
One cal = 4.184 J
or
1J = 0.2390 cal.
Energy Transformations
if molecules collide with enough
force to break them into atoms, a
ELEMENT
CHEMICAL REACTION
can take place
hydrogen molecule, H2
COMPOUND
MIXTURE
ELEMENT
oxygen molecule, O2
a mixture of
hydrogen and
oxygen molecules
water, H2O
2 H2 + O2
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.
2 H2O +
E
The Zeppelin LZ 129 Hindenburg catching fire on May
6, 1937 at Lakehurst Naval Air Station in New Jersey.
S.S. Hindenburg
• German zeppelin
luxury liner
• Exploded on
maiden voyage
• Filled with
hydrogen gas
35 people died when the Hindenburg exploded.
May 1937 at Lakehurst, New Jersey
Hydrogen is the most effective buoyant gas,
but is it highly flammable. The disastrous fire
in the Hindenburg, a hydrogen-filled dirigible,
in 1937 led to the replacement of hydrogen
by nonflammable helium.
Exothermic vs. Endothermic
Decomposition of Nitrogen Triiodide
Decomposition of
Nitrogen Triiodide
N2
NI3
2 NI3(s)
I2
N2(g) + 3 I2(g)
Direction of Heat Flow
Surroundings
EXOthermic
qsys < 0
ENDOthermic
qsys > 0
System
H2O(s) + heat  H2O(l)
H2O(l)  H2O(s) + heat
melting
freezing
System
Kotz, Purcell, Chemistry & Chemical Reactivity 1991, page 207
Conservation of Matter
Reactants
yield
Products
Conservation of Energy
in a Chemical Reaction
In this example, the energy
Endothermic
of the reactants
Reaction
and products increases,
while the energy of the surroundings decreases.
Reactant + Energy
Product
In every case, however, the total energy does not change.
Surroundings
Energy
Surroundings
System
System
Myers, Oldham, Tocci, Chemistry, 2004, page 41
Before
reaction
After
reaction
Conservation of Energy
in a Chemical Reaction
In this example, the energy
Exothermic
of the reactants
Reaction
and products decreases,
while the energy of the surroundings increases.
Reactant
Product + Energy
In every case, however, the total energy does not change.
Energy
Surroundings
Myers, Oldham, Tocci, Chemistry, 2004, page 41
System
Before
reaction
Surroundings
System
After
reaction
Exothermic Reaction
-DH Exothermic
Reactants  Products + Energy
10 energy
=
8 energy
+ 2 energy
Energy of reactants
Energy
Energy of products
Reactants
-DH Exothermic
Products
Reaction Progress
Endothermic Reaction
+DH Endothermic
Energy + Reactants  Products
2 energy + 8 energy
= 10 energy
Energy of reactants
Energy
Energy of products
Products
Reactants
+DH Endothermic
Reaction progress
Heat Capacity
and
Specific Heat
Thermal Expansion
• Most objects e-x-p-a-n-d when heated
• Large structures such as bridges must be
built to leave room for thermal expansion
• All features expand together
COLD
HOT
Cracks in sidewalk.
Specific Heat
Specific Heat
Heat absorbed
or released
specific heat
mass in
grams
Specific Heats
of Some Substances
Specific Heat
Substance (cal/ g oC)
Water
Alcohol
Wood
Aluminum
Sand
Iron
Copper
Silver
Gold
1.00
0.58
0.42
0.22
0.19
0.11
0.093
0.057
0.031
(J/g oC)
4.18
2.4
1.8
0.90
0.79
0.46
0.39
0.24
0.13
Examples:
How much heat is absorbed when a 4.68 g
piece of metal experiences a temperature
change of 182°C? (Cp = .301 J/g°C)
q = m Cp ΔT
= (4.68 g)(.301 J/g°C)(182°C)
= 256.37 J
=256 J (answer in 3 sig figs)
Examples:
The temperature of a sample of water
increases from 20.0°C to 46.6°C as it absorbs
5650 J of heat. What is the mass of the
sample?
ΔT = 46.6°C – 20.0°C = 26.6 °C
q = m Cp ΔT
5650 J = m (4.184 J/g°C)(26.6°C)
5650 J = m (111.2944 J/g)
111.2944 J/g 111.2944 J/g
m = 50.766 g or 50.8 g
Try:
How much heat is released to the
surroundings when 200 g of water at 96.0 °C
cools to 25.0 °C?
Answer = 59 400 J