Energy and Phase Changes Notes Page | 14
Unit 8: Energy and Phase Changes
(Link to Prentice Hall Text: Chapters 10 & 11)
Name:______
Date Due / Assignments / Page Number: Problem NumbersAssignment 1: Vapor Pressure and Boiling Point / 289: 35, 36, 37, 38, 39,
Assignment 2: Heat Conversions & Exothermic/Endothermic Processes / 322: 41, 45
Assignment 3: Phase Changes and Heat Calculations / 322: 53a,b,d, 70, 72
Phases of Matter
The Kinetic Molecular Theory explains all of the properties of matter that we can observe.
It says that:
1.
2.
3.
4.
Let’s summarize some properties of the three phases of matter:
Property / Solid / Liquid / GasShape
Volume
IMFs
Energy of Particles
Density
Compressibility
Particle diagram
Phases depend on two things:
1.
2.
Energy
Matter -
Energy-
Forms of Energy:
What is a Calorie?
Specifically, a calorie is the amount of energy, or heat, it takes to raise the temperature of 1 gram of water 1 degree Celsius (1.8 degrees Fahrenheit). One calorie is equal to 4.184 joules, a common unit of energy used in the physical sciences.
Most of us think of calories in relation to food, as in "This can of soda has 200 calories." It turns out that the calories on a food package are actually kilocalories (1,000 calories = 1 kilocalorie). The word is sometimes capitalized to show the difference, but usually not. A food calorie contains 4,184 joules. A can of soda containing 200 food calories contains 200,000 regular calories. Other countries do use joules to describe food energy.
What is the coldest possible temperature?
Absolute Zero
1. This occurs at ______or ______.
2. To convert between Kelvin (K) and degrees Celsius (°C) use: ______.
Practice with Temperature Conversions
If the temperature is given in degrees Celsius, convert to Kelvin. If the temperature is given in Kelvin, convert to degrees Celsius.
Energy and Phase Changes Notes Page | 14
1. 73°C ______
2. 297K______
3. 353K______
4. 100°C______
5. 37°C______
6. 0°C______
7. 65°C______
8. 0K______
9. 450K______
10. 77K______
Energy and Phase Changes Notes Page | 14
Energy and Phase Changes Notes Page | 14
Understanding Pressure
Pressure is defined as ______.
Pressure =
Units of Force =
Units of Area =
Units of Pressure =
What happens to pressure in a vacuum?
Conversion Factors for pressure
Standard Pressure = 1 atm1atm =
Math with Pressure
1. What happens to pressure as area increases?
2. Convert the pressure of 955 mmHg to each of the following units.
Energy and Phase Changes Notes Page | 14
a. Atmospheres
b. Kilopascals
c. Torr
d. Pascals
e. Newtons per square meter
Energy and Phase Changes Notes Page | 14
3. What do we mean by atmospheric pressure? What causes this pressure?
4. How do we measure atmospheric pressure? Is atmospheric pressure the same everywhere on the surface of the earth?
5. Why is the fluid in a barometer mercury, rather than water or another liquid?
Manometer Readings
Calculate the pressure of the gas in the following manometers.
Vapor Pressure and Boiling Point
Vapor Pressure
What happens when no more liquid can evaporate into the gaseous phase at a given temperature in a closed container?
What is vapor pressure?
What is vapor pressure a measure of?
How does vapor pressure change as temperature increases?
Do all liquids have the same vapor pressure at a given temperature? Why?
Boiling Point
What requirement must be met for a liquid to boil?
What is the difference between evaporation and boiling?
Practice with Table H
1. At what temperature would propanone boil at an atmospheric pressure of 150 kPa?______
2. At what temperature would ethanol boil at an atmospheric pressure of 150 kPa? ______
3. At what temperature would water boil at an atmospheric pressure of 150 kPa? ______
4. At what pressure would water boil at 75°C? ______
5. At what pressure would water boil at 110°C? ______
6. What is the normal boiling point of ethanoic acid? ______
7. What is the normal boiling point of propanone? ______
8. Which has stronger intermolecular forces of attraction – ethanoic acid or propanone? ______
Above and Beyond: Critical Thinking with Vapor Pressure and Boiling Point
1. If the vapor pressure of an alcohol is greater than the vapor pressure of water at a given temperature, which would boil at a lower temperature?
2. What happens to the boiling point of water as you climb a mountain? Why?
3. What happens to the cooking time of rice as you climb a mountain?
4. What happens to the boiling point of water in a pressure cooker?
Phase Diagrams Type One: When Heat is Added to a System
A Heating Curve: Heat is ENTERING the system, therefore the changes are ______.
Endothermic Process are denoted with the symbol ______.
The following is a heating curve for a substance starting below its freezing point.
Name of Phase or Transition / Equation to Calculate Heat Energy / Potential Energy Change? / Kinetic Energy Change?A → B
B → C
C →D
D → E
E → F
Type Two: When Heat is Removed From a System
A Cooling Curve: Heat is EXITING the system, therefore the changes are ______.
Exothermic Process are denoted with the symbol ______.
The following is a cooling curve for a substance starting above its boiling point.
Name of Phase or Transition / Equation to Calculate Heat Energy / Potential Energy Change? / Kinetic Energy Change?A → B
B → C
C →D
D → E
E → F
Calculating the Kinetic Energy in a Thermal Account
Calculation of Heat For a Substance Undergoing a Temperature Change
The heat (q) transferred into or out of a substance undergoing a temperature change depends on three different variables:
(1)
(2)
(3)
Final Equation:
Exercise 8.4: Calculating Heat During a Temperature Change
1. The specific heat of ethanol is 2.46 J/goC. Find the heat required to raise the temperature of 193 g of ethanol from 19oC to 35oC.
2. When a 120 g sample of aluminum (Al) absorbs 9612 J of energy, its temperature increases from 25oC to 115oC. Find the specific heat of aluminum. Be sure to include the correct unit for specific heat.
3. The specific heat of lead (Pb) is 0.129 J/goC. Find the amount of heat released when 2.4 g of lead is cooled from 37.2oC to 22.5oC.
4. How many kJ of energy are needed to raise the temperature of 165 g of water from 10.55oC to 47.32oC?
(Hint: How many J are in 1 kJ?)
5. A small pebble is heated and placed in a foam cup calorimeter containing 25.0 mL of water at 25.0°C. The water reaches a maximum temperature at 26.4°C. How many joules of heat were released by the pebble?
Calculation of Heat For a Substance Undergoing a Phase Change
The heat transferred into or out of a substance undergoing a phase change depends on different variables:
(1)
(2)
(3)
Final Equation for Evaporation/Condensation:
Final Equation for Melting/Fusion:
Calculating Heat During a Phase Change
1. How many joules of heat are required to melt 255g of ice at 0°C?
2. How much heat must be added to vaporize 50.0g of water at 100°C and 101.3kPa?
3. How much heat is required to boil away 175g at 100oC and 101.3 kPa?
Putting it all together.
Specific heat capacity water =4.187 J/g*oC Specific heat capacity ice = 2.108 J/g* oC
Specific heat capacity water vapor = 1.996 J/g* oC
1. How much heat is required to boil away all 6.00g of a piece of ice, originally at -10°C
2. A 25.00 gram sample of water vapor at 120.0°C is cooled until it all becomes ice at -20°C. How much energy is released?
3. How much heat must be added to turn liquid 13.0 grams water at 17oC to steam at 112oC? (Assume standard pressure)
Phase Diagrams
Phase Equilibria
Freezing:
Melting :
Condensation:
Vaporization:
Sublimation:
Deposition:
Interpreting Phase Diagrams
Triple Point:______
Critical Point:______