temperature temperature scales fahrenheit 212 o f 180 o f 32 o f celcius 100 o c 0 o c kelvin 373 k...
TRANSCRIPT
Temperature
Temperature Scales
Fahrenheit
212 oF
180 oF
32 oF
Celcius
100 oC
100 oC
0 oC
Kelvin
373 K
100 K
273 K
Boiling point of water
Freezing point of water
Notice that 1 kelvin degree = 1 degree Celcius1 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
Fast Slow“HOT” “COLD”
Kinetic Energy (KE) = ½ m v 2
*Vector = gives direction and magnitude
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
Kinetic energy
Fra
ctio
ns o
f pa
rtic
les
lower temperature
higher temperature
TOTALKinetic ENERGY
= Heat= Heat
Molecular Velocities
speed
Fra
ctio
ns o
f pa
rtic
les many different molecular speeds
molecules sorted by speed
the Maxwell speed distribution
http://antoine.frostburg.edu/chem/senese/101/gases/slides/sld016.htm
Hot vs. Cold Tea
Kinetic energy
Many molecules have anintermediate kinetic energy
Few molecules have avery high kinetic energy
Low temperature(iced tea)
High temperature(hot tea)
Perc
ent o
f mol
ecul
es
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 Cold Water90 oC 10 oC
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 291
Water Molecules in the same temperature water
Water(50 oC)
Water(50 oC)
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 291
Temperature vs. Heat
Measuredwith a
Calorimeter
TotalKineticEnergy
Joules(calories)
Measuredwith a
Thermometer
AverageKineticEnergy
oCelcius(or Kelvin)
Alike Different
A Propertyof
Matter
HaveKineticEnergy
Heat
Different
Topic Topic
Temperature
Energy
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.
(a) Radiant energy (b) Thermal energy
(c) Chemical energy (d) Nuclear energy (e) Electrical energy
The energy something possesses due to its motion, depending on mass and velocity.
Potential energy
Energy in Energy out
kinetic energy kinetic energy
Energy
Kinetic Energy – energy of motion
KE = ½ m v 2
Potential Energy – stored energy
Batteries (chemical potential energy)
Spring in a watch (mechanical potential energy)
Water trapped above a dam (gravitational potential energy)
mass velocity (speed)
B
AC
is the ability to do work or produce heat
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
KE = ½ m v 2 KE = ½ m v
2
BUS BULLET
KE(bus) = ½ (10,000 lbs) (0.5 mph)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
Potential Energy energy due to the composition or position of an object. (Chemical Potential Energy – energy stored in a substance because of its composition. The potential energy results from the arrangement of the atoms and the strength of the bonds that join them. Stored energy is released when bonds are broken.)
Kinetic Energy
energy of motion
Energy
Heat – symbol is q; energy in the process of flowing from a warm object to a cooler one
Work – weight lifted through a height
Units of energy
calorie where 1 calorie (cal) is the amount of energy needed to raise the temperature of 1 g of water by 1°C.
Most common units of energy
joule (J), defined as 1(kilogram•meter2)/second2, energy is also expressed in kilojoules (1 kJ = 103J).
Units of energy are the same, regardless of the form of energy
One cal = 4.184 J or
1J = 0.2390 cal.
metric
kilocalorie called a Calorie with a capital “C” sometimes called nutritional calories 1 Calorie = 1000 calories
SI
Energy Transformations
ELEMENTELEMENT
hydrogen molecule, H2
ELEMENTELEMENT
oxygen molecule, O2
MIXTUREMIXTURE
a mixture ofhydrogen and oxygen molecules
CHEMICAL REACTIONCHEMICAL REACTION
if molecules collide with enoughforce to break them into atoms, a can take place
COMPOUNDCOMPOUND
water, H2O
2 H22 H2 O2
O2 2 H2O2 H2O++ ++ EE
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.
The Zeppelin LZ 129 Hindenburg catching fire on May 6, 1937 at Lakehurst Naval Air Station in New Jersey.
S.S. Hindenburg
35 people died when the Hindenburg exploded.
May 1937 at Lakehurst, New Jersey
• German zeppelin luxury liner
• Exploded on maiden voyage
• Filled with hydrogen gas
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
2 NI3(s) N2(g) + 3 I2(g)
NI3 I2
N2
Direction of Heat Flow
Surroundings
ENDOthermicqsys > 0
EXOthermicqsys < 0
System
Kotz, Purcell, Chemistry & Chemical Reactivity 1991, page 207
System
H2O(s) + heat H2O(l)
meltingmelting
H2O(l) H2O(s) + heat
freezingfreezing
Conservation of Matter
Reactants yield Products
Conservation of Energy in a Chemical Reaction
Surroundings
System
Surroundings
SystemEn
erg
y
Beforereaction
Afterreaction
In this example, the energy of the reactants and products increases, while the energy of the surroundings decreases.
In every case, however, the total energy does not change.
Myers, Oldham, Tocci, Chemistry, 2004, page 41
Endothermic Reaction
Reactant + Energy Product
Conservation of Energy in a Chemical Reaction
Surroundings
System
Surroundings
System
En
erg
y
Beforereaction
Afterreaction
In this example, the energy of the reactants and products decreases, while the energy of the surroundings increases.
In every case, however, the total energy does not change.
Myers, Oldham, Tocci, Chemistry, 2004, page 41
Exothermic Reaction
Reactant Product + Energy
Exothermic Reaction
Reactants Products + Energy 10 energy = 8 energy + 2 energy
Reactants
Products
Ene
rgy
Energy of reactants
Energy of products
Reaction Progress
-H Exothermic
-H Exothermic
Endothermic Reaction
Energy + Reactants Products
+H Endothermic
Reaction progress
Ene
rgy
Reactants
Products
2 energy + 8 energy = 10 energy
+H Endothermic
Energy of reactants
Energy of products
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
COLDHOT
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) (J/g oC)
Water 1.00 4.18Alcohol 0.58 2.4Wood 0.42 1.8Aluminum 0.22 0.90Sand 0.19 0.79Iron 0.11 0.46Copper 0.093 0.39Silver 0.057 0.24Gold 0.031 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)
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
Examples:
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