Naming Binary Compounds Containing a Metal and a Nonmetal Pisgah High School M. Jones.
Last rev. 5/12/04 Pisgah High School Chemistry Mr. Jones Heat, Temperature And Phase Changes.
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Transcript of Last rev. 5/12/04 Pisgah High School Chemistry Mr. Jones Heat, Temperature And Phase Changes.
Last rev. 5/12/04
Pisgah High School Chemistry
Mr. Jones
Heat, Temperature
And
Phase Changes
Part OneHeat and
Temperature
What temperature does the thermometer indicate?
What might be going on that would cause this temperature?
This is the view out the window, past the thermometer.
Yep.
It is snowing.
Why would snow cause the air temperature to be at precisely 0C?
What occurs at 0C?
Water freezes and ice melts.
Ice, in the form of snow, falls through the slightly warmer air.
Ice melts at 0 C, so the air cools to that temperature.
The snow melts and absorbs heat from the air,
causing the air to cool.
The temperature hovers at zero Celsius as the snow melts.
So why is there snow on the ground if it is melting?
Yep. That’s what allows the snow to accumulate.
As the snow melts, it absorbs heat and cools the ground, the car, and the grill.
This allows more snow to lay. It doesn’t melt because the ground is now at 0C.
What is temperature?
What does it mean to have a temperature of 0 C?
Is temperature the same
thing as heat?
Temperature is a measure of how “hot” or “cold” something is.
Temperature is measured in arbitrary units, like Fahrenheit or Celsius.
Temperature is proportional to the average kinetic energy of the molecules of the substance.
T ½ mv2
Temperature is therefore proportional to the speed of the molecules of a substance.
T ½ mv2
Velocity or speed
T v
The higher the temperature, the greater the average speed of the molecules.
T ½ mv2
Velocity or speed
T v
Heat is the thermal energy transferred from a hot object to a cold object.
Heat is measured in energy units -- Joules or calories.
The heat transferred is proportional to the mass of the object, the specific heat capacity of the object and the temperature change the object undergoes.
Heat has the symbol q and is calculated using …
q = mcT
q = mcT
Quantity of heat
mass
specific heat capacity
temperature change
q = mcT
Quantity of heat
specific heat capacity
The specific heat capacity of water
is 4.18 J/gC
q = m c T
How much heat is needed to raise the temperature of 25.6 grams of water from 20.0 C to 50.0 C?
q = (25.6g)(4.18J/gC)(30.0C)
q = 3210 J
q = m c T
What is the final temperature of 27.0 grams of liquid water, initially at 0C, after it absorbs 700.0 J of energy?
Hint: start by solving for T.
=qT m c
Answer: 6.20 C
Part TwoCalorimetry and
Specific Heat Capacity
Calorimetry is a collection of laboratory procedures used to investigate the transfer of heat.
In calorimetry experiments, one might be looking for a final temperature or a specific heat capacity.
Investigate:
Suppose two different masses of water at different temperatures are mixed. Can you predict the final temperature?
Will the final temperature be cooler than the cool water, or will it be warmer than the warm water?
Or will the final temperature be somewhere in between?
Investigate:
Investigate:
Develop a procedure where you could mix a known mass of cool water with a different mass of water at an elevated temperature and measure the final (equilibrium) temperature.
What equipment would you need?
You could use a balance, a thermometer, a coffee cup calorimeter, and a hot plate.
Investigate:
Develop a procedure where you could mix a known mass of cool water with a different mass of water at an elevated temperature and measure the final (equilibrium) temperature.
What do you need in a data table?
Investigate:
Mass of calorimeter cupMass of cool waterInitial temperature of cool waterMass of warm waterInitial temperature of hot waterFinal temperature after mixing
Feel free to make additions.
Investigate:Whenever we design an experiment we make some assumptions. Here are a couple, can you add any more?
The calorimeter cup is a perfect insulator and no heat is exchanged with the surroundings.
Note: Hot plates and boiling water can cause severe burns.
Investigate:
You might need a hint about how to calculate the results.
What is the law of conservation of energy?
Energy is neither created nor destroyed, only changed in form.
Investigate:
You might need a hint about how to calculate the results.
The law of conservation of energy suggests that the heat lost by the hot water as it cools is equal to the heat gained by the cool water as it warms up.
Investigate:
To put it mathematically:
qlost = -qgained
And since q = mcT then
mhcTh = -mccTc
Heat lost by the hot water =
Heat gained by the cold water
Investigate:
Finally, since T includes the final temperature (T = Tfinal – Tinitial ) then replace T:
mhc(Tf -Th) = -mcc(Tf -Tc)
Write an equation that solves for the final temperature.
Investigate:
Calculate the final temperature when 20.0 grams of water at 85 C is added to 35.0 grams of water at 10.0 C in an insulated container.
Use your equation to solve the following problem:
Investigate:
Calculate the final temperature when 20.0 grams of water at 85 C is added to 35.0 grams of water at 10.0 C in an insulated container.
The answer to the following problem is 37.3 C.
In the next investigation you will …develop a method to
find the specific heat capacity of a metal.
Specific heat capacity …
1. …varies from one substance to another
2. …a measure of how much heat something can “hold”
3. …the amount of heat needed to raise one gram of a substance by one Celsius degree
Specific heat capacity …
1. …varies from one substance to another
2. …a measure of how much heat something can “hold”
3. …the amount of heat needed to raise one gram of a substance by one Celsius degree
Specific heat capacity lab suggestions:
1. Heat a metal to a known temp 2. Transfer the metal to a known
quantity of water at a known temperature
3. Measure the equilibrium temperature
4. Use qlost = qgained to compute the specific heat of the metal.
hotplate
Get the initial temperature of the metal.
The temperature of boiling water.
metal
Get initial temp of water in calorimeter cup.
Transfer the metal to the calorimeter.
Continue stirring until thermal equilibrium is reached.
Data: Mass of metalInitial temp of metal
Mass of waterInitial temp of water
Final temp of water and metal
qlost = -qgained
mmcmTm = -(mwcwTw)
-(mwcwTw)
mmTm
cm =
Data: Suppose 104.58 g of a metal is heated to 100. C.
It is placed into 54.21 g of water at 17.5 C.
The final temp of water and metal is 22.0 C.
What would be the specific heat capacity of the metal?
Data: Suppose 104.58 g of a metal is heated to 100. C.
It is placed into 54.21 g of water at 17.5 C.
The final temp of water and metal is 22.0 C.
What could be the identity of the metal?
Aluminum 0.900Bismuth 0.123Copper 0.386Brass 0.380Gold 0.126Lead 0.128Silver 0.233Tungsten 0.134Zinc 0.387Mercury 0.140Ethanol 2.400Water 4.186Ice 2.050
Substancec in
J/g KTable of selected specific heats.
Part ThreeCalorimetry and Phase Changes
Is heat is absorbed or released during a phase change?
How could you measure the heat absorbed or released as
substances change phase?
Consider ice melting in water.
1. Does the temperature of the water change?
2. Is the water absorbing or releasing heat?
3. Does ice absorb heat or release heat as it melts?
Consider ice melting in water.
1. Does the temperature of the water change?
2. Is the water absorbing or releasing heat?
3. Does ice absorb heat or release heat as it melts?
No
Releasing heat
Absorb heat
Consider ice melting in water.
The word fusion means “melting”.
How could you design an experiment to measure
the heat of fusion of ice?
Consider ice melting in water.
You could measure the heat lost by some water as it cools.
That should equal the heat gained by the ice as it melts.
Ice
Consider ice melting in water.
Suppose some ice at 0C is placed into 50.00 g of water at 25.5 C.
Ice
Copy down this information and the data that follows.
Consider ice melting in water.
When the system reaches equilibrium at 0C, 15.95 grams of the ice has melted.
Ice
Consider ice melting in water.
Knowing that the heat lost by the water as it cools to 0C is equal to the heat gained by the ice as it melts at 0C …
Ice
Consider ice melting in water.
…we should be able to compute the heat of fusion of ice, Hf.
qlost by water= qgained by ice
mwatercT = miceHf
Ice
Consider ice melting in water.
Go ahead and calculate the value of Hf.
qlost by water= qgained by ice
mwatercT = miceHf
Ice
We now know that heat is absorbed or released during a phase change.
Heat is absorbed as solids melt, or liquids vaporize.
Heat is released as liquids freeze, or vapors condense.
We now know that heat is absorbed or released during a phase change.
Ice And melts.
Heat is absorbed by the ice.
Heat is absorbed by the ice.
… making liquid water
One gram of ice at 0C absorbs 334 J as it melts to form water at 0C.
water
Heat is released by the water as it freezes.
334 joules is released when one gram of water freezes at 0C.
Ice
Ice
Ice absorbs 334 J per gram as it melts at 0C
Water releases 334 J per gram as it freezes at 0C
Heat is absorbed by the water as it vaporizes.
Hotplate
2260 joules is absorbed by one gram of water as it boils at 100C.
Hotplate
Heat is absorbed by the water as it vaporizes.
Hotplate
Water absorbs
2260 J/g as it boils at 100 C
Steam releases 2260 J/g as it condenses at 100 C
Heat is released by water vapor as it condenses.
Heat is released by water vapor as it condenses.
The heat released by condensing water vapor is a major factor in weather phenomena like thunderstorms and hurricanes.
40,000 + feet
Thunderhead
The heat released by condensing water vapor causes convection and updrafts in thunderstorms.
Phase changes occur at a constant temperature as heat is absorbed or released.
If phase changes occur at a constant temperature, then what happens to the heat when water boils?
Question for discussion:
a. Heat energy is converted to matter (E=mc2) and it stays in the water.
b.The heat increases the speed of the water molecules.
c. The heat energy breaks the intermolecular bonds which keep the water in the liquid phase.
d.The temperature really does change, you just missed it.
Question for discussion – possible answers:
a. Heat energy is converted to matter (E=mc2) and it stays in the water.
b.The heat increases the speed of the water molecules.
c. The heat energy breaks the intermolecular bonds which keep the water in the liquid phase.
d.The temperature really does change, you just missed it.
Question for discussion – possible answers:
a. Heat energy is converted to matter (E=mc2) and it stays in the water.
b.The heat increases the speed of the water molecules.
c. The heat energy breaks the intermolecular bonds which keep the water in the liquid phase.
d.The temperature really does change, you just missed it.
Question for discussion – possible answers:
The heat gained or lost in phase changes can be calculated using …
q = mHf q = mHv
Heat of fusion
(melting)
Heat of vaporization
The values for water are …
Hf = 334 J/g
Hv=2260 J/g
Heat of fusion
(melting)
Heat of vaporization
How much heat is absorbed by 150.0 g of ice as it melts at 0C?q = m Hf q = (150.0 g)(334 J/g)
q = 50,100 J or 50.1 kJ
How much heat is released by 20.0 grams of steam as it condenses at 100C?q = m Hv q = (20.0 g)(2260 J/g)
q = 45,200 J or 45.2 kJ
Part FourSublimation
and Phase Diagrams
Sublimation is an unusual phase change.
Sublimation occurs when a solid changes directly into a gas without going through the liquid phase.
Heat is absorbed when sublimation occurs.
Dry Ice
Dry ice is solid carbon dioxide, CO2.
At room temperature and normal atmospheric pressures dry ice undergoes sublimation.
It goes directly from the solid state to the
vapor state.
CO2 vapor
Dry Ice
Dry ice is solid carbon dioxide, CO2.
At room temperature and normal atmospheric pressures dry ice undergoes sublimation.
It goes directly from the solid state to the
vapor state.
CO2 vapor
CO2 vapor
CO2 vapor
CO2 vapor
CO2 vapor
Solid iodine, I2, also undergoes sublimation when heated.
Hotplate
Watchglass
Beaker with iodine
Iodine vapor fills the beaker.
Solid iodine crystallizes on the bottom of the watchglass.
Hotplate
Watchglass
Beaker with iodine
The color of the vapor fades as the iodine deposits on the watchglass
A solid forming directly from the vapor is called deposition.
Hotplate
Watchglass
Beaker with iodine
The color of the vapor fades as the iodine deposits on the watchglass
Heat is absorbed as the iodine undergoes sublimation.
Heat is released as the iodine undergoes
deposition.
A phase diagram can help explain why dry ice undergoes sublimation.
Temperature
Pre
ssur
e
The phase diagram has three distinct regions.
2
31
Which phase is in each region?
Temperature
Pre
ssur
e
The phase diagram has three distinct regions.
2
31
Which phase is in each region?
Temperature
Pre
ssur
e
1= ???
1
2
3
2= ???
3= ???
Hint: What happens to ice as temperature increases?
Which phase is in each region?
Temperature
Pre
ssur
e
1= Solid
1
2
3
2= ???
3= ???
Hint: What happens to ice as temperature increases?
Which phase is in each region?
Temperature
Pre
ssur
e
1= Solid
1
2
3
2= Liquid
3= ???
Hint: What happens to ice as temperature increases?
Which phase is in each region?
Temperature
Pre
ssur
e
1= Solid
1
2
3
2= Liquid
3= Gas
Hint: What happens to ice as temperature increases?
The point where all three phases exist in equilibrium is called the
Temperature
S L
G
triple point. triple point.
Pre
ssur
e
At a pressure of 1 atm, most substances go through all three phases, as the temperature increases,
Temp.
S L
G1 atm
Solids melt to form liquids, which vaporize to form gases.
Temp.
S L
G1 atm
MP BP
Notice the melting point and boiling point.
At a pressure of 1 atm, most substances go through all three phases, as the temperature increases,
But the phase diagram for CO2 is a little different.
Temperature
S L
G1 atm
Notice that the triple point is above 1 atm.
5 atm
At 1 atm CO2 goes directly from solid to vapor as the temperature increases.
Temperature
S L
G1 atm
At 1 atm CO2 goes directly from solid to vapor as the temperature increases.
Temperature
S L
G1 atm
The sublimation point is –78.5 C
-78.5
Temperature
Pre
ssur
e
Tell what phase change the
arrow indicates.
An arrow will appear in the following phase diagrams.
What phase change is occurring?
Melting (fusion)
Temperature
Pre
ssur
e
S L
G
What phase change is occurring?
Temperature
Pre
ssur
e
VaporizationS L
G
What phase change is occurring?
Temperature
Pre
ssur
e
CondensationS L
G
What phase change is occurring?
Temperature
Pre
ssur
e
SublimationS L
G
What phase change is occurring?
Temperature
Pre
ssur
e
Liquefying a gas by increasing the pressure.
S L
G
Part FiveHeating and Cooling
Curves
A process that gives off heat is called
exothermic.
A process that absorbs heat is called endothermic.
Exothermic:
Endothermic:
FreezingCondensationDeposition
Melting (fusion)
VaporizationSublimationHeat is absorbed.
Heat is released.
Investigate:
Either recall an earlier experiment, or design an experiment to look at the temperature of water as phase changes take place.
Investigate:
The following are suggested procedures you could use to record the temperature of water at regular intervals.
Note: Hot plates and boiling water can cause severe burns.
1. Clamp a thermometer with the bulb in a mixture of ice and water in a beaker on a hot plate. (The hot plate is off.)
2. Allow the temperature to equilibrate.3. Turn on the hot plate and continue to
record temperature at regular intervals until some of the water boils away.
4. Plot temperature as a function of time.
Investigate:
Thermometer
Stirring hotplate
TimeTem
pera
ture
Graph paper
Thermometer
Stirring hotplate
TimeTem
pera
ture
Graph paper
You could use a thermometer and
plot the temperature on graph paper or
on a computer.
Thermometer
Stirring hotplate
Time
Tem
pera
ture
CBL, LabPro, or computer
0.0 C
Stirring hotplate
Time
Tem
pera
ture
Temperature probe Or you could use a
thermometer probe connected to an interface and a
computer to plot the temperature.
CBL, LabPro, or computer
0.0 C
Stirring hotplate
Time
Tem
pera
ture
Temperature probe
Phase changes occur at a single temperature.
Water freezes and ice melts at 0C.
At sea level, water boils and steam condenses at 100C.
Consider the following heating curve for water.
0
100
Time
Temp
0
100
Time
Temp
Ice at –30C absorbs heat. Temperature rises to 0C.
Consider the following heating curve for water.
0
100
Time
Temp
Ice at 0C absorbs heat and melts at constant 0C to make water at 0C.
Consider the following heating curve for water.
0
100
Time
TempWhen all ice melts, water at 0C absorbs heat and temperature rises to 100C.
Consider the following heating curve for water.
0
100
Time
Temp
Water absorbs heat and boils at a constant temperature of 100C.
Consider the following heating curve for water.
0
100
Time
Temp
Temperature of steam rises as it
absorbs heat after all of the water boils.
Consider the following heating curve for water.
What is happening at each segment of the heating curve?
0
100
Time
Temp
Look at the different regions of the heating curve for water.
0
100
Time
Temp
Ice
Ice andwater
Water
Water andsteam
Steam
Phase changes?
The temperature is constant during a phase change.
0
100
Time
Temp
Ice
Ice andwater
Water
Water andsteam
Steam
Phase changes
Calculating heat at each segment of the heating curve.
0
100
Time
Temp
q1=mciT
The temperature of the ice is
increasing. The specific heat for ice
is 2.05 J/gC.
Calculating heat at each segment of the heating curve.
0
100
Time
Temp
q2=mHf
q1=mciT
A phase change occurs at a constant
temperature. Use the heat of fusion
since ice is melting.
Calculating heat at each segment of the heating curve.
0
100
Time
Temp
q2=mHf
q1=mciT
q3=mcwT The temperature of the water is
increasing. The specific heat of water
is 4.18 J/gC.
Calculating heat at each segment of the heating curve.
0
100
Time
Temp
q2=mHf
q1=mciT
q3=mcwTq4=mHv
A phase change occurs at a constant
temperature. Use the heat of vaporization
since water is boiling.
Calculating heat at each segment of the heating curve.
0
100
Time
Temp
q2=mHf
q1=mciT
q3=mcwTq4=mHv
q5=mcsT
The temperature of the steam is
increasing. The specific heat of steam
is 2.02 J/gC.
Calculating heat at each segment of the heating curve.
0
100
Time
Temp
q2=mHf
q1=mciT
q3=mcwTq4=mHv
q5=mcsT
Use q=mcT when there is a
temperature change.
Calculating heat at each segment of the heating curve.
0
100
Time
Temp
q2=mHf
q1=mciT
q3=mcwTq4=mHv
q5=mcsT
Use q=mHf or q=mHv when there is a phase change.
Calculating heat at each segment of the heating curve.
0
100
Time
Temp
q2=mHf
q1=mciT
q3=mcwTq4=mHv
q5=mcsT
The total amount of heat absorbed is the sum:
qtot= q1+q2+q3+q4+q5
What would the cooling curve of steam look like?
0
100
Time
Temp
What would the cooling curve of steam look like?
0
100
Time
Temp
IceIce andwater
Water
Water andsteam
Steam
What would the cooling curve of steam look like?
0
100
Time
Temp
IceIce andwater
Water
Water andsteam
Steam
Heat energy is released at each step.
There is something else special about a mixture of ice and water.
Suppose ice and water were placed into a perfectly insulated
container. The mixture would stay at a constant zero degrees Celsius by establishing an equilibrium.
An ice/water equilibrium occurs when the rate at which water freezes is equal to the rate at which ice melts.
The amount of ice and water will never change.
If the container is completely insulated.
Ice and water in an insulated container.
Acme Digital Thermometer0.0 C
Some ice melts and forms liquid water.
Acme Digital Thermometer0.0 C
Some water freezes and forms ice.
Acme Digital Thermometer0.0 C
When the rates at which the ice melts and the water freezes are equal …
Acme Digital Thermometer0.0 C
equilibrium is
established.
Acme Digital Thermometer0.0 C
… an
The amounts of ice and water will remain constant…
Acme Digital Thermometer0.0 C
…and the mixture of ice and water will remain at a constant 0C.
Acme Digital Thermometer0.0 C
A mixture of ice and water can be used to calibrate a thermometer at 0C.
Acme Digital Thermometer0.0 C
Questions
2. A substance freezes at -80.0C. At what temperature does it melt?
1. Ice and water are placed in an insulated container. What will be the equilibrium temperature?
Questions
3. A liquid gradually turns solid at a constant temperature. Is heat being added, or removed?
4. How does melting snow affect the air temperature?
Questions
5. When water vapor condenses to form liquid water, is heat released or absorbed?
6. What is the connection between condensing water vapor and updrafts in thunderstorms?
Questions
7. Explain how sweating cools your body.
8. Explain how liquid water evaporating from a roadway can cause ice to form on the road.
Questions
9. Explain why dry ice doesn’t form a puddle of liquid CO2.
10. What phase change is occuring?
Temperature
Pre
ssur
e
Questions
11. How many joules of heat are released when 50.0 grams of water cools from 80.0C to 20.0C?
12. How many joules of heat are needed to melt 15.0 grams of ice at 0C?
Questions
13. How many joules of heat are needed to take 15.0 grams of ice at –20.0C to steam at 150.0C?
14. How many grams of steam must cool from 125.0C to 80.0C to release 2.00 x 106 J of energy?Hint: there are three changes that take place.
Heat
Temperature Phase change
Melting
BoilingFreezing
CondensationSublimation
Equilibrium Joule
Calorie
Celsius
Deposition
VaporizationHeating curve
Phase diagram