Post on 21-Dec-2015
transcript
Friday, April 11, 2014
• Grab a Lab from my Desk:– Read through the front page.
• Today:– System vs. Surroundings– Endothermic vs. Exothermic– Chemical vs. Physical– Perform Lab
• Water means tap water
Unit 11Hot/Cold Packs
7.1 Endothermic and Exothermic
7.2 Calorimetry and Heat Capacity
7.3 Changes in State
Introductory Activity
• How many things can you think of in everyday life that either give off heat or absorb heat?
• Which of these things are physical processes?• Which are chemical processes?
Chemical vs. Physical
• Physical and chemical processes both can both produce heat (which will make it feel hot) or absorb heat (which will make it feel cold)
• Physical – The actual chemicals are not changed, and can often be re-cooped.– Examples: scratching, cutting, dissolving, breaking.
• Chemical – The actual chemicals react to form new different chemicals.
Hot/Cold Packs
Transfer of energyTransfer of energy
Use
System & Surroundings
System & Surroundings
between
Materials ability to absorb energy
without noticeable temperature change
Materials ability to absorb energy
without noticeable temperature change
Effect on temperature depends on
Physical change
Physical change
Is determined with
CalorimetryCalorimetry
Can be done in
Chemical change
Chemical change
System vs. Surroundings
• System:– The chemicals that are involved in the chemical/physical
process
• Surroundings:– The things that are surrounding those chemicals:
• Water, beaker, air, lab . . . . the universe
Endothermic & Exothermic
• Endothermic:– When the system absorbs energy from the surroundings.– Tends to feel cold.
• Exothermic:– When the system releases energy to the surroundings.– Tends to feel hot.
SECTION 7.1 -ENDOTHERMIC AND EXOTHERMIC
System & Surroundings
• The system is only made of the molecules undergoing the change
• The surroundings are everything else– The water molecules & the container– Your hand, the air, the thermometer
• Note that water is made up of water molecules—not a solid chunk of water…but for this picture, it’s best to represent water as one thing since it’s the surroundings and focus on the molecules reacting as the system.
Exothermic & You
• You touch the beaker and it feels hot• Energy is being transferred TO YOU• You are the surroundings• When energy moves from system to
surroundings, it’s exothermic
Exothermic & the Thermometer
• The temperature (measured by the thermometer) is related to the average kinetic energy of the molecules in the container
• The majority of the molecules in a solution are water
• If the temperature is increasing, the energy of the water molecules is increasing
• Since water is the surrounding (it’s not actually reacting), energy is being transferred to the surroundings
• Exothermic shows an increase in the temperature within the container
Endothermic
• The opposite is also true• If the container feels cold to you, energy is
being transferred FROM YOU (the surroundings) into the system—endothermic
• If the thermometer goes down, energy is being transferred FROM the water molecules (surroundings) into the system--endothermic
Let’s Practice
Example:Identify the system and surroundings when you hold an ice cube while it
melts. Is this endo- or exothermic?
System: Water molecules in the form of iceSurroundings: You and the air
It feels cold to you…so energy is leaving you (surroundings)
When energy goes from surroundings to system it’s endothermic
Please sit in your new seat
• Remember:– Your row is your lab group– No more than 4 people per row– No empty seats in front of row
Monday, April 14, 2014
• Today:– Notes/Demonstrations of:
• Energy Flow (Change in Energy)• Exothermic and endothermic.• Units of Energy
• Homework:– Energy Conversions
Enthalpy
http://commons.wikimedia.org/wiki/Image:Hot_Horseshoe_%28stevefe%29.jpg
• Enthalpy (H) - total energy of system• ’s in enthalpy are usually measured:
– As ’s occur H can be measured– H is measured in kJ
Fe(s, 300K) Fe(s, 1100K) H=20.1 kJ– indicates that as it is heated by 800 K, its
enthalpy increases by 20,100 J for each mole of iron
Types of Processes (Reactions)
Exothermic• Exo – “out of”• Energy flows out of the
reaction into surroundings.– Surroundings get warmer– Heat, light, vibrations,
explosions
• H is negative
Endothermic• Endo – “into”, “inside of”• Energy flows into the
reaction from the surroundings– Surroundings get colder
• H is positive
Energy Diagram 1
Exothermic!
Energy Diagram 2
Endothermic!
Demonstrations
Demo 1
• 20 g Ba(OH)2
• 10 g ammonium thiocyanate
• Place in beaker on a wet wooden board.
• Mix thoroughly.
• * Danger! Energy Change!
Demo 2• 5.0 g KMnO4• 1 mL glycerin• Evaporating dish• Place KMnO4 in a pile in
the evaporating dish• Make a well w/ scoopula• Add glycerin & stand
back
• * Danger! Energy Change!
Temperature
• Temperature – proportional to the average kinetic energy of the molecules
• Kinetic Energy - Energy due to motion (Related to how fast the molecules are moving)
As temperature increases
Molecules move faster
Heat & Enthalpy
• Heat (q)– The flow of energy from higher temperature particles to lower temperature particles
• Enthalpy (H)– Takes into account the internal energy of the sample along with pressure and volume
• Under constant pressure (lab-top conditions), heat and enthalpy are the same…we’ll use the term “enthalpy”
Energy Units
• The most common energy units are Joules (J) and calories (cal)
• These equivalents can be used in dimensional analysis to convert units
4.184 J 1.00 cal
1000 J
1000 cal
1 kJ
1 Cal (food calorie)
=
=
=
Energy Equivalents
Tuesday, April 15, 2015
• Pickup Papers on Red Lab Table• Today:
– Go Over Test– Go Over Energy Conversions/Endo Exothermic– Tutoring/Extra Help– ThermoStoich
• Homework:– Complete ThermoStoich Worksheet– Check @lths.org email – sent on Friday
Wednesday, April 16, 2014
–Turn in ThermoStoich on my Desk–Grab a Heat Capacity Worksheet
• Today:–Notes: Heat Capacity–Homework:
• Heat Capacity Worksheet• Bring Books/Notes/Calc. tomorrow
Heat Capacity
• Specific Heat Capacity (c) – The amount of energy that can be absorbed before 1 g of a substance’s temperature has increased by 1°C
• c for liquid water – 4.184 J/g°C
Heat Capacity
High Heat Capacity• Takes a large amount of
energy to noticeably change temp
• Heats up slowly
• Cools down slowly
• Maintains temp better with small condition changes
Low Heat Capacity• Small amount of energy
can noticeably change temperature
• Heats up quickly
• Cools down quickly
• Quickly readjusts to new conditions
• A pool takes a long time to warm up and remains fairly warm over night.
• Lake Michigan . . .• Pizza . . . • The air warms quickly
on a sunny day, but cools quickly at night
• A cast-iron pan stays hot for a long time after removing from oven.
• Aluminum foil can be grabbed by your hand from a hot oven because it cools so quickly
Substance Heat Capacity
J/g°CH2O(l) 4.184
Aluminum 0.890
Iron 0.450
Mercury 0.140
Carbon 0.710
Silver 0.240
What things affect temperature change?
• Heat Capacity of substance– The higher the heat capacity, the slower
the temperature change
• Mass of sample– The larger the mass, the more molecules
there are to absorb energy, so the slower the temperature change
TCmq
Energy added or removed
Mass of sample
Specific heat capacity of substance
Change in temperature
Example
TCmq
q = change in energym = massC = heat capacity DT = change in temperature (T2 - T1)
TCg
JgJ
184.445285
Example:If 285 J is added to 45 g of water at 25°C, what is the
final temperature? C water = 4.184 J/g°C
T
CgJg
J
184.445
285
12 TTT
CT 51.1
12 TTT
CCCT 51.262551.12
Let’s Practice #1
TCmq
q = change in energym = massCp = heat capacity DT = change in temperature (T2 - T1)
q = - 4707.00J
CCg
Jgq 0.750.3018.40.25
Example:How many joules must be
removed from 25.0 g of water at 75.0°C to drop the
temperature to 30.0°? Cp water = 4.184 J/g°C
Let’s Practice #2
TCmq
q = change in energym = massC = heat capacity DT = change in temperature (T2 - T1)
TCg
JgJ
900.00.30437
Example:If the specific heat capacity of
aluminum is 0.900 J/g°C, what is the final temperature if 437 J is added to a 30.0 g
sample at 15.0°C
T
CgJg
J
900.00.30
437
12 TTT
CT 19.16
12 TTT
CCCT 19.310.1519.162
Thursday, April 17, 2014
• Grab a worksheet • Today:
– Pick up a handout.– Begin Calorimetry
• Homework:– Calorimeter Problems
• Tuesday:– Meet in the Maroon Room. Cool Demos.
CALORIMETRY
Intro to Calorimetry Problem: How much water was in the cup?
25 g Fe
T of Electrified device = 780 °C
Initial T of water = 25 °CFinal T of water = 42 °C
Remember:• q=mc∆T is an equation for
1 substance, not 2!• Energy is always
conserved.• Ciron=0.46 J/g°C
Conservation of Energy
• 1st Law of Thermodynamics – Energy cannot be created nor destroyed in physical or chemical changes– This is also referred to as the Law of
Conservation of Energy
• If energy cannot be created nor destroyed, then energy lost by the system must be gained by the surroundings and vice versa
Calorimetry
• Calorimetry – Uses the energy change measured in the surroundings to find energy change of the system
• The energy lost/gained by the surroundings is equal to but opposite of the energy lost/gained by the system.
qsurroundings = - qsystem
(m×C×DT)surroundings = - (m×C×DT)system
• Don’t forget the “-” sign on one side• Make sure to keep all information about
surroundings together and all information about system together.
Two objects at different temperatures . . .
• Thermal Equilibrium – Two objects at different temperatures placed together will come to the same temperature
• So you know that T2 for the system is the same as T2 for the surroundings!
Metal:m = 23.8 gT1 = 100.0°CT2 = 32.5°CC = ? Water:m = 50.0 gT1 = 24°CT2 = 32.5°CC = 4.184 J/g°C
Cp = 1.04 J/g°C
watermetal qq
watermetal TCmTCm
CC
CgJgCCCg
5.245.32184.40.500.1005.328.23
CCg
CCCg
JgC p
0.1005.328.23
5.245.32184.40.50
An example of CalorimetryExample:
A 23.8 g piece of unknown metal is heated to 100.0°C and is placed in 50.0 g of water at 24°C water. If the final temperature of the water is 32.5°,what is the heat capacity of
the metal?
Example:A 10.0 g of aluminum (specific heat capacity
is 0.900 J/g°C) at 95.0°C is placed in a container of 100.0 g of water (specific heat capacity is 4.184 J/g°C) at 25.0°C. What’s
the final temperature?
Metal:m = 10.0 gT1 = 95.0°CT2 = ?C = 0.900 J/g°C Water:m = 100.0 gT1 = 25.0°CT2 = ?C = 4.184 J/g°C T2 = 26.47 °C
watermetal qq
watermetal TCmTCm
CT
CgJgCTCg
Jg
0.25184.40.1000.95900.00.10 22
Let’s Practice #2
CTCT 0.254.418950.9 22
104604.4188550.9 22 TT
113150.427 2 T
4.427
113152 T
Friday, April 25, 2014
• Today:– Nova Video on Making “Stuff”
• Next week:– Calorimetry Lab– Heating/Cooling Curves– Review ThermoChemistry Unit– Test on ThermoChemistry
Monday, April 28, 2014
• Today:– Nova Video on Making “Stuff” #2
• This Week:– Calorimetry Lab– Heating/Cooling Curves– Review ThermoChemistry Unit– Test on ThermoChemistry
Tuesday, April 29, 2014
• Grab a lab from my desk• Today:
– Spend the first 3 min starting the prelab– Go over the prelab– Work in PAIRS on the lab.
• Tomorrow:– Heating/Cooling Curves
• Reminder: Test on Friday
Thursday, April 25, 2013• Have out your Calorimetry Worksheet from last
week.• Pick up a Virtual Calorimetry Lab.• Today:
– Go Over Homework– Work on Lab
• Work in partners• Each is responsible for writing• Staple together and hand in before you leave• Finish INDIVIDUALLY for homework if you don’t
Calorimetry Worksheet
1. 0.451 J/g○C
2. 0.401 J/g○C
3. 40.0 g
4. 0.836 J/g○C
5. a. 627,600 J
b. 627,600 J
c. 150,000 J
d. 150 Cal
Friday, April 26, 2013
• Turn in your lab if you didn’t yesterday.• Pick up papers from the Red Lab Table• Today:
– Questions from papers that were passed back?– Thermo-stoichiometry– Work on Thermo-stoich worksheet – turn in before you leave– Begin working on a review
• Monday:– Review
• Tuesday:– Test
Enthalpy & Rx Type
• Enthalpy is abbreviated H
• We can measure changes in enthalpy . . .
• If H = + value– Reaction requires energy– endothermic
• If H = - value– Reaction looses energy– exothermic
What does this mean?H2 + Br2 2HBr + 36.4 kJ
• If 1 moles of H2 are reacted with excess Br2, how much energy is produced?– 36.4 kJ
• If 2 moles of H2 are reacted with excess Br2, how much energy is produced?– 72.8 kJ
• We have a mole/energy ratio!
What does this mean Continued?H2 + Br2 2HBr + 36.4 kJ
• If 1 moles of Br2 are reacted with excess H2, how much energy is produced?
• If 2 moles of Br2 are reacted with excess H2, how much energy is produced?– 36.4 kJ
• We have a mole/energy ratio!
An example of Thermo w/ Stoichiometry
• How much heat will be released when 6.44 g of sulfur reacts with excess O2 according to the following equation?
2S + 3O2 2SO3 ∆H=-791.4 kJ
6.44 g S 1 mol S
32.07 g S
kJ
mol S79.5 kJ
791.4
2
Monday, April 29, 2013
• Pickup Heating/Cooling Curve Worksheet• Today:
– Go Over Thermo-Stoichiometry– Notes on Heating/Cooling Curves– Work on Worksheet for Heating/Cooling Curves
• Tomorrow:– Review
• Wednesday:– Test on ThermoStoichiometry
SECTION 7.3 -CHANGES IN STATE
What’s happening when a frozen ice pack melts?
The energy being put into the system is used for breaking IMF’s, not increasing motion (temperature)
Change in State
To melt or boil, intermolecular forces must be broken
Breaking intermolecular forces requires energy
A sample with solid & liquid will not rise above the melting point until all the solid is gone.
The same is true for a sample of liquid & gas
Melting
• When going from a solid to a liquid, some of the intermolecular forces are broken
• All samples of a substance melt at the same temperature, but the more you have the longer it takes to melt (requires more energy).
Vaporization
• When going from a liquid to a gas, all of the rest of the intermolecular forces are broken
• All samples of a substance boil at the same temperature, but the more you have the longer it takes to boil (requires more energy).
Solid
Liquid
Gas
Melting
Vaporizing or Evaporating
Condensing
Freezing
Incr
easi
ng m
olec
ular
mot
ion
(tem
pera
ture
)
Changes in State go in Both Directions
Going the other way
• The energy needed to melt 1 gram is the same as the energy released when 1 gram freezes.– If it takes adding 547 J to melt a sample,
then removing 547 J would be released when the sample freezes.
• The energy needed to boil 1 gram is the same as the energy released when 1 gram is condensed.– If it takes 2798 J to boil a sample, then
2798 J will be released when a sample is condensed.
Example
vapHmH
H = enthalpy (energy)m = mass of sampleHfus = enthalpy of fusion
gcalgH 2.547)5.157(
DH = - 8.6×104 cal
Example:How much energy is
released with 157.5 g of water is condensed?
Hvap water = 547.2 cal/g
Since we’re condensing, we need to “release” energy…DH will be negative!
Heating curve of water
-50
0
50
100
150
Energy input
Te
mp
era
ture
Heating Curves
Melting & Freezing
Point
Boiling & Condensing
Point
Heating curves show how the temperature changes as energy is added to the sample
Heating curve of water
-50
0
50
100
150
Energy input
Te
mp
era
ture
Going Up & Down
+DH
-DH
Moving up the curve requires energy, while moving down releases energy
Heating curve of water
-50
0
50
100
150
Energy input
Te
mp
era
ture
States of Matter on the Curve
Gas OnlyEnergy added
increases temp
Liquid & gasEnergy added breaks remaining IMF’s
Liquid OnlyEnergy added
increases temp
Solid & LiquidEnergy added breaks IMF’s
Solid OnlyEnergy added
increases temp
Heating curve of water
-50
0
50
100
150
Energy input
Te
mp
era
ture
Different Heat Capacities
Gas OnlyC = 2.01 J/g°C
Liquid OnlyC = 4.184 J/g°C
Solid OnlyC = 2.13 J/g°C
The solid, liquid and gas states absorb water differently—use the correct C!
Tuesday, April 30, 2013
• Pick up work on Red Lab Table• Have out your homework• Today:
– Go Over Answers to Homework– Work on Review
• Tomorrow:– Test Unit 11
1. 1,3,5
2. 2,4
3. 2,4
4. 1,3,5
5. 1,3,5
6. 2,4
7. 2 min
8. 6.5 min
9. 22 min
10.endothermic
11. Scratch out
12. 1.8 min
13.13.5 min
14.1
15.5
16.Enthalpy of vaporization is greater than Enthalpy of fusion.
1. 5 C
2. 15 C
3. 5 C
4. A
5. C
6. E
7. B
8. D
9. B, D
10.A, C, E
11.D
12.B
Monday, April 4, 2011
• BoHA:– Turn in your March Madness if you have it complete. Do not turn it
in later.– Pick up a packet, and scantron.
• Today:– New MoleBucks– Makeups for Unit 11 Test?– ACT Practice
• Mark answers both in your booklet and your ScanTron!
• Homework:– Try to work out a logical solution the answer to the problem given.
If you don’t have an answer, at least come up with some logic to help you along tomorrow.
Intro to Calorimetry Problem: How much water was in the cup?
25 g Fe
T of Electrified device = 780 °C
Initial T of water = 25 °CFinal T of water = 42 °C
Remember:• q=mc∆T is an equation for
1 substance, not 2!• Energy is always
concerved.• Ciron=0.46 J/g°C
Tuesday, April 5, 2011
• BoHA:– If you weren’t here yesterday, pickup ACT,
ScanTron and a handout.
• Today:– Pass Back ACT (I need ScanTron back)– New Seats– Introductory Calorimetry Problem (solve in
groups)– Notes on Calorimetry
• Homework:– Calorimetry Problems Worksheet
CALORIMETRY
Intro to Calorimetry Problem: How much water was in the cup?
25 g Fe
T of Electrified device = 780 °C
Initial T of water = 25 °CFinal T of water = 42 °C
Remember:• q=mc∆T is an equation for
1 substance, not 2!• Energy is always
concerved.• Ciron=0.46 J/g°C
Conservation of Energy
• 1st Law of Thermodynamics – Energy cannot be created nor destroyed in physical or chemical changes– This is also referred to as the Law of
Conservation of Energy
• If energy cannot be created nor destroyed, then energy lost by the system must be gained by the surroundings and vice versa
Calorimetry
• Calorimetry – Uses the energy change measured in the surroundings to find energy change of the system
• The energy lost/gained by the surroundings is equal to but opposite of the energy lost/gained by the system.
qsurroundings = - qsystem
(m×C×DT)surroundings = - (m×C×DT)system
• Don’t forget the “-” sign on one side• Make sure to keep all information about
surroundings together and all information about system together.
Two objects at different temperatures
• Thermal Equilibrium – Two objects at different temperatures placed together will come to the same temperature
• So you know that T2 for the system is the same as T2 for the surroundings!
Metal:m = 23.8 gT1 = 100.0°CT2 = 32.5°CC = ? Water:m = 50.0 gT1 = 24°CT2 = 32.5°CC = 4.184 J/g°C
Cp = 1.04 J/g°C
watermetal qq
watermetal TCmTCm
CC
CgJgCCCg
5.245.32184.40.500.1005.328.23
CCg
CCCg
JgC p
0.1005.328.23
5.245.32184.40.50
An example of CalorimetryExample:
A 23.8 g piece of unknown metal is heated to 100.0°C and is placed in 50.0 g of water at 24°C water. If the final temperature of the water is 32.5°,what is the heat capacity of
the metal?
Example:A 10.0 g of aluminum (specific heat capacity
is 0.900 J/g°C) at 95.0°C is placed in a container of 100.0 g of water (specific heat capacity is 4.184 J/g°C) at 25.0°C. What’s
the final temperature?
Metal:m = 10.0 gT1 = 95.0°CT2 = ?C = 0.900 J/g°C Water:m = 100.0 gT1 = 25.0°CT2 = ?C = 4.184 J/g°C T2 = 26.47 °C
watermetal qq
watermetal TCmTCm
CT
CgJgCTCg
Jg
0.25184.40.1000.95900.00.10 22
Let’s Practice #3
CTCT 0.254.418950.9 22
104604.4188550.9 22 TT
113150.427 2 T
4.427
113152 T
Wednesday, April 6, 2011
• BoHA:–Grab a RSG for Unit 12
• Today:–Go Over Calorimetry Problems–Questions from Homework–ACT Questions?–Find specific heat of a metal.–Start RSG for Next Unit
Answers to Homework
1. 0.451 J/g°C
2. 0.401 J/g°C
3. 40.0 g
4. 0.836 J/g°C
5. multipart answers:a) 1,230,000 J are absorbed
b) 1,230,000 J are released
c) 294,000 calories
d) 294 Calories